Dynamic Electrochemistry Methodology and Application обзор 1994

Anal. Chem. 1994, 66, 360R-427R

Dynamic Electrochemistry: Methodology and Application Michael D. Ryan

Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233

Edmond F. Bowden

Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695

James Q. Chambers'

Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996

Review Contents

Books and Reviews Mass Transport

Microelectrodes Hydrodynamic Methods

Analytical Voltammetry Methodologies Stripping Voltammetry Catalytic Methods Derivatization Methods .Analytical Use of Micelles Pulse and Sweep Methods Metal/Ligand Complexation Studies Chemometric Approaches

Electron-Transfer Theories Heterogeneous Kinetics Homogeneous Kinetics Double-Layer Studies Adsorption Studies

Surface Electrochemistry Theoretical Aspects Mercury Electrodes Carbon Electrodes Single Crystal Surfaces Surface Imaging Techniques Polycrystalline Electrodes Miscellaneous Electrodes

Charge Transport in Polymer Films Electrocatalysis at Modified Electrodes Ion-Exchange Polymer Film Electrodes Ionophore Films Redox Polymer Films Electrochromism and Pattern Formation

Polymer Electrodes Conducting Polymer Electrodes Self-Assembled Monolayers Other Modified Electrodes

Heterogeneous/Homogeneous Kinetics

Modified Electrodes

Bioelectrochemistry

360R 363R

368R

371R

374R

383R

in

392R

360R

Books and Reviews Small Molecules of Biological Importance Protein Electrochemistry Enzyme Electrodes Polynucleotides and Nucleic Acids In Vivo and Cellular Electrochemistry Immunological and Recognition-Based

Electrochemistry

Analytical Chemistry, Vol. 66, No. 12, June 15, 1994

404R Miscellaneous Bioelectrochemical Studies

Characterization of Redox Reactions Electron-Transfer Mechanisms Organic Electrochemistry Organometallic Electrochemistry Inorganic Electrochemistry Activation of Small Molecules Electrosynthesis Micelles and Surfactants

Spectroelectrochemistry 407R Instrumentation 410R

This article reviews the literature of electroanalytical chemistry in the period between December 1991 and the end of November 1993. An attempt was made to minimize the gap in the coverage between this and the previous Dynamic Electrochemistry review in Analytical Chemistry ( A I ) .

The focus of this review is on fundamental advances and practical applications of electrochemistry that pertain to electroanalytical chemistry. Topics covered include ultramicroelectrodes, analytical voltammetry, electrode kinetics, surface electrode phenomena, modified electrodes, bioelectrochemistry, characterization of inorganic, organic, and organometallic redox couples, spectroelectrochemistry, and instrumentation. The subject is of course quite broad and the divisions overlap. It is perhaps easier to indicate topics not covered in detail. Applications where there is no net current flow, e.g., potentiometric sensors, have traditionally been covered elsewhere in this review issue. There is not a separate section on photoelectrochemistry in the present review, although citations to articles relating to this topic can be found throughout the review. For the most part, articles were excluded that dealt with exotic electrode materials or media where the emphasis was not electroanalytical in nature. Industrial electrochemistry, fuel cells, and battery applications were also omitted from the coverage.

The literature cited below was selected by scanning Citation Index, CA Selects: Electrochemical Reactions, C A Selects: Analytical Electrochemistry, and our personal reading of the literature. The coverage is not exhaustive, but is intended to highlight important developments and activity.

A. BOOKS AND REVIEWS Three accounts of a historical nature on square-wave and

pulse voltammetry have appeared, in part commemorating

0 1994 American Chemical Society 0003-2700/94/0366-0360$14.00/0

Mlchael D. Ryan is Associate Professor of Chemistry at Marquette University. I n 1969 he received his B.S. degree from the University of Notre Dame and in 1973 he was awarded a Ph.D. from the University of Wisconsin, Madison. Before joining the faculty of Marquette University in 1974, he served as Lecturer at the University of Arizona. His current interests include the study of indirect reduction of nitrite, nitric oxide, and sulfite reductases and the kinetics of electron-transfer reactions of biological compounds.

Edmond F. Bowden is currently an associate professor in the Department of Chemistry at North Carolina State Univer- sity and a member of the Biotechnology Faculty. After earning a B.S. degree in aerospace engineering at Syracuse Uni- versity in 1970, he spent several years working in the aerospace and chemical industries before returning to school. He obtained his Ph.D. at Virginia Common- wealth University in 1982 under the guid- ance of Fred M. Hawkridge and then held a postdoctoral appointment at the Univer- sity of Minnesota with John F. Evans before moving to NCSU. His. research interests include interfacial bioelectrochemistry, biological electron transfer and bioenergetics, enzyme electrodes for bioanalysis, and electroactive monolayers.

James Q. Chambers earned his A.B. degree in chemistry from Princeton Uni- versity in 1959. His graduate work under the direction of Ralph N. Adams was conducted at the University of Kansas, where he received the Ph.D. degree in 1964. The research interests of Prof. Chambers are in the general area of electroanalytical chemistry and are focused primarily on understanding and characterizing electrode reactions involving organic, polymeric, and biologically important compounds.

the original publication of Barker 40 years ago (A2-A4). Osteryoung also makes a passionate case for the advantages and virtues of pulse voltammetry in an Accounts of Chemical Research article (A5). Of practical value is the IUPAC commission on electroanalytical chemistry review on the effects that arise in pulse voltammetry when adsorption of the reactant is significant (A6).

Several monographs or reviews have appeared recently that would make suitable reading for beginning students at various levels. Koryta has written a short introduction to ionic solutions, electrochemistry, and membrane phenomena that emphasizes concepts and is nonmathematical in nature (A7). A practical treatment of classical polarography also avoids mathematical detail (A8). Run0 and Peters have written an undergraduate level introduction to concepts involving electrode potentials (A9). At the graduate level, the monograph by Gileadi on electrode kinetics is especially noteworthy (AZO). This text does a remarkable job of covering the fundamental concepts of electrode kinetics as well as presenting clear introductory descriptions of modern techniques, experimental details, and applications to batteries, fuel cells, corrosion, and electroplating.

A number of impressive edited compilations of chapters on topics related to some aspect of electrochemical science have been published in the last two years. Before detailing these,

we will note the extensive, multiauthor review on the current state of understanding and research on the electrode/ electrolyte interface by Bard et al. (A2 2). This report focuses on new experimental capabilities and outstanding issues in three areas: structural characterization, dynamics, and materials aspects of the electrode/electrolyte interface. Elsewhere, Bard has speculated on future directions of electrochemistry in a provocative article (A22). Areas mentioned included UMEs and unusual media, scanning probe microscopies, and molecular biology.

Three volumes of Modern Aspects of Electrochemistry have appeared (A23425) . Volume 25 has chapters on hydrogen ingress in metals, charge transfer across liquid/ liquid interfaces, dc techniques for measurement of corrosion rates, ellipsometry, and electrical breakdown in liquids. Volume 23 contains chapters on ion and electron transfer across monolayers of organic surfactants, determination of current distributions by Laplace transformation, cathodic protection engineering, semiconductor/metal cluster surfaces, and electrical breakdown in anodic oxide films. Continuing with the eclectic nature of this series, Volume 24 treats nerve excitation, membrane energy transduction, the chlor-alkali process, bioelectrochemical field effects, electronic factors in charge-transfer reactions, and electrodeposition of metal powders with controlled particle grain size and morphology. In similar manner, a compilation with a high-sounding title (A26) contains chapters on the double layer, in situ spectroscopic examination of electrodes, electrode kinetics, organic electrochemistry, high-temperature electrochemistry, corrosion, and others.

The most recent volume of Advances in Electrochemical Science and Engineering (A2 7) contains four chapters: Trasatti on electrocatalysis of the HER, Hammou on solid oxide fuel cells, Richmond on second harmonic generation at single crystal electrodes, and Deslouis and Tribollet on flow modulation techniques. Lipkowski and Ross have edited two volumes of generally high caliber reviews relating to fundamental surface science at electrode interfaces (A28, A29). The first, which deals with adsorption of molecules, contains several chapters on radiochemical and spectroscopic characterization of adsorbed layers. The second, which is a collection of major reviews on the structure of the metal/ electrolyte interface, includes chapters by vacuum surface experimentalists, theorists, and electrochemists. Among the latter are reports by Ross on surface crystallography, Kolb on surface reconstruction, and Soriaga on molecular adsorption a t single crystal electrodes. Omitted from the previous Analytical Chemistry review (A I ) was mention of a compilation that contained chapters on the structure of halides and small organic molecules on metal surfaces by Hubbard, on heterogeneous catalysis of substitution reactions by Spiro, on the kinetics of crystallization of solids from aqueous solution by House, and a general introduction to corrosion of metals by Hammond (A20). In yet another volume one can learn about the semiconductor/electrolyte interface, electrode potentials, and energy scales, the application of STM to electrochemistry, adsorption and electron transfer at interfaces, and various electrochemical aspects of biomembranes (A22).

Two reviews of solvent effects on electron-transfer reactions have appeared (A22, A23). Weaver’s article is mostly

Analytical Chemistry, Vol. 66, No. 12, June 15, 1994 361R

nonmathematical and emphasizes concepts. Galus sum- marizes theoretical treatments of the reaction rates for both soluble couples and amalgam-forming reactions such as Zn2+/ Zn(Hg). In a review by Saveant of his contributions to our understanding of dissociative electron-transfer reactions, he outlines criteria for distinguishing between stepwise and concerted mechanisms in electrode reactions (A24) .

Trasatti has reviewed recent theory on the adsorption of organics on electrode surfaces (A25), and Parsons and Ritzoulis critically compare experimental results for adsorption on stepped surfaces of Pt and Au single crystal electrodes (A26) . In the latter article, the evidence for the assignment of voltammetric peaks in the hydrogen region to hydrogen atom adsorption on steps of surface unit cells was clearly summarized. A thorough review of UHV techniques as applied toobtain atomic level information about the electrode interface at single crystal electrodes has been provided by Soriaga (A27). This treatment is suitable for a graduate student level introduction to the area.

A substantial analysis of the kinetics of oxygen reduction at solid electrodes in aqueous solution has been written by Appleby (A28) , and a book has appeared on the electrochemistry of surfaces from the critical perspective of Professor J. O’M. Bockris (A29) . Catalysis of the hydrogen ion reduction by metal surfaces has been briefly reviewed (A30) .

An IUPAC Commission report has appeared that compiles kinetic parameters on the C12/C1- electrode reaction (A31) . Also the IUPAC Commission report dealing with the measurement of real surface areas has been published a second time (A32) . This report describes 15 methods, 11 in situ and 4 ex situ, in detail.

A variety of ancillary techniques for the study of electrode processes are treated in a recent volume; included are chapters on ellipsometry, inferometric methods, SERS, Mossbauer spectroscopy, photothermal deflection spectroscopy, X-ray absorption and neutron scattering, impedance spectroscopy, and others (A33) . An introduction to STM and AFM with emphasis on basic theory and practicalities has appeared that discusses the application of these techniques to in situ electrochemistry (A34) . Scanning tunneling spectroscopy, which can map the surface electronic structure with atomic resolution in the best scenario, was also addressed.

Buttry and Ward have written perhaps the most authoritative of several recent reviews on electrochemical quartz crystal microscopy (EQCM) (A35) . Hillman et al. also reviewed the QCM technique with emphasis on the detection of mobile species transferred during the redox switching of polymer films (A36) . A review of electrochemical mass spectroscopy (ECMS) contains some excellent examples of the use of a thermospray LC/MS interface with an electrochemical cell (A37). Solution IR spectroelectrochemistry has also been briefly reviewed (A38) . Recent applications of spectroelectrochemistry have been described in a report that focuses on the redox chemistry of thin-film interfaces, e.g., inorganic semiconductors, oxide and chalcogenide films on native metals, dye-modified electrodes, conducting polymer films, and others (A39) .

Volume 18 of the Bard series, Electroanalytical Chemistry, contains reviews on electrochemistry in microheterogeneous fluids by Rusling, charge transport in polymer-modified

electrodes by Inzelt, and SECM by Bard et al. (A40) . Inzelt has also reviewed polymer film electrodes elsewhere (A41) .

Microelectrodes have been covered thoroughly in a publication of the proceedings of a NATO advanced study institute that contains articles from most of the laboratories which have contributed to the development of this area (A42). The authoritative review by Heinze on this subject is also recommended (A43) .

The latest in the Techniques in Chemistry series deals with the molecular design of electrode surfaces. Nine individual chapters written by active mod squad researchers cover subjects such as adsorption on single crystal electrodes, various aspects of redox polymer electrodes, and self-assembled monolayers. The volume, which includes more than 1400 references, is tightly edited by Royce Murray, who contributed a highly recommended overview chapter (A44). Reviews in this area have appeared elsewhere (A45-A49). The articles by Forster and Vos on the theory and applications of modified electrodes (A45) and by Zagal on electrocatalytic processes at metal- lophthalocyanine surfaces (A46) are nicely done.

Several reviews treat subjects that strongly overlap electrochemistry and the amorphous, but fashionable, area of materials science. The chapter on processable conducting polymers in a compilation containing five chapters on nonlinear optics and conducting polymers is especially noteworthy (A50). Mirkin and Ratner have produced a provocative treatise on molecular electronics (A.71) and electrochemistry at high-T, superconducting working electrodes, an area where electrochemistry can contribute to both fabrication and characterization, is the subject of a report (A52). Other reviews treated the structure and physical properties of PEO-type polymer electrolytes (A53) and the electrochemical synthesis and properties of conducting polymers (A54) . The article by Curran et ai. narrowly focused on the various methods by which polypyrrole can be employed as a support for electrocatalytic materials or substituent groups (A55) .

Recent work toward the development of practical biosensors has been reviewed from several different viewpoints (A56- A62) . These devices are generally based around a redox enzyme coupled with a molecular mediating species entrapped in an interfacial matrix of some kind. Both amperometric and potentiometric detection can be employed. The review of Alvarez-Icaza and Bilitewski gave a good summary of design parameters and their optimization (A56). Thearticleof Wring and Hart (A61) concentrated on the chemistry of the modification of carbon-based substrates for these devices, while that of Hilditch and Green had a practical bent describing disposable electrochemical biosensors in or near to commercial production (A62).

Ewing et al. have reviewed progress on the difficult problem of analyzing the contents of single nerve cells with emphasis on in vivo electrochemistry and EC detection for capillary electrophoresis where the Penn State group has made major contributions (A63) .

Several works have appeared that concern more classical analytical voltammetry. These include a little monograph by Smyth on the voltammetry of biologically important molecules (A64) and reviews of analytical voltammetry theory by Cassidy (A65) , adsorptive cathodic stripping voltammetry by van den Berg (A66) , the reduction of metal complexes on Hg by

362R Analytical Chemistry, Vol. 66, No. 12, June 15, 1994

Tur’yan (A67) , and instrumentation for voltammetry by Barisci et al. (A68) . In addition, a bookon cyclicvoltammetry has been recently advertized (A69) .

In the realm of organic electrochemistry, several important books or reviews have been published in recent years. A revised and expanded third edition of the Manual Baizer opus has appeared (A70) . To complement this work, a book based on a symposium in honor of Manny Baizer contains 48 chapters organized under the following headings: Mechanism; Reduc- tion; Oxidation; Mediated Reactions; Biochemical, Biomass and Natural Products; Modified, Sacrificial/Consumable Electrodes; Electrogenerated Bases; Film-Forming Electro- polymerization; and Ion-Exchange (A71) . Professor Shono has written a brief text that features experimental details for 150 electrochemical transformations of specific compounds (A72) . Niyazymbetov and Evans have summarized the use of carbanions and heteroatom anions in electroorganic synthesis (A73) . Recent examples of in situ generation of anions and anodic oxidation of anions are given. Commercial applications are emphasized in a brief review of the use of sacrificial anodes in synthetic electrochemical processes involving C02 (A74) . The problem of C02 reduction has also been treated from several different angles in a collection of chapters by different authors (A75) . Other reviews have appeared on the electrosynthesis of polymers with emphasis on intermediates (A76) and on the electrochemistry of chlorophyll (A77) .

Two excellent treatments of important topics have been produced by authorities in their respective fields. Wayner and Parker have provided an Accounts of Chemical Research article on the thermodynamic relationships between bond dissociation energies and redox potentials of the derived radicals and their corresponding ions (A78). A clear description is given here of the way to incorporate voltammetric peak potential data into the thermodynamic cycles. Koval and Howard have presented a thorough review of electron transfer at semiconductor electrode/liquid electrolyte interfaces (A79) . While the emphasis of this review is on research advances since 1985, it also serves well as a lucid introduction to the terms and fundamental concepts of a complex subject. Gratzel has given an account of his research on photoelectrochemical energy conversion using a “molecular machine” based on thin films of colloidal Ti02 particles that are sintered together to allow for charge carrier transport (A80, ,481). The phenomenon of room-temperature photoluminescence from porous Si was reviewed in comprehensive fashion (A82) , and a review of photoemission at metal/electrolyte interfaces includes a discussion of the cathodic generation of solvated electrons (A83) . An issue of Electrochimica Acta was devoted to new trends in photoelectrochemistry (A84) .

Finally, two issues of the Journal of Electroanalytical Chemistry have accounts of the scientific careers and useful complete lists of their publications for two stalwarts of physical electrochemistry: Professors Brian Conway and John O’Mara Bockris in Vols. 355 and 357, respectively (A85, A86) .

6. MASS TRANSPORT Microelectrodes. Theory. The intense activity in the area

of microelectrode theory has lessened in the last few years. Applications of UMEs have mushroomed, however, and there

have been some important and useful papers published that deserve mention here.

In the latter category, Mirkin and Bard have presented a theoretical analysis of quasi-reversible steady-state voltammograms that allows extraction of the kinetic parameters (ko and a ) from a single i-E curve without independent determination of the Eo’ value ( B I ) . They gave extensive tables for the wave shape parameters, E114 - E112 and E112 - E3149 that correlate with given sets of kinetic parameters. Cor- relation tables were given both for the case of uniformly accessible electrodes, such as a RDE and an UME hemisphere, and for a UME disk. Another procedure that appears to be easy to implement for the determination of heterogeneous rate constants from CV peak separation data is that of Lavagnini et al., which only requires intermediate diffusion control such that peak currents are evident in the CVs (B2) .

Exact formalism for the ac impedance of spherical, cylindrical disk, and ring UMEs was developed (B3) . Real and imaginary components of the impedance, assuming uniform flux at the electrode surface, were tabulated as a function a2w/D, a dimensionless quantity where a is the characteristic dimension of the UME, w is the frequency, and D is the diffusion coefficient of the Ox/R couple. Linear sweep voltammograms obtained at ring electrodes were calculated over 9 orders of magnitude sweep rate and compared to experimental results (B4) . Calculation of the theoretical voltammograms required the value of a dimensionless parameter, y = (R2 + R1)/2(R2 - Rl), where R2 and R1 are the outer and inner ring radii, respectively.

Oldham has continued his penetrating theoretical examination of microelectrode behavior in a very general treatment of steady-state voltammetry at UMEs of arbitrary shape (B5). He showed that the steady-state current depends on three factors: the electrode area, an accessibility factor, and a heterogeneity function. A universal equation is given for the i-E relationship.

A sophisticated integral equation approach was used by Bender and Stone to treat steady-state mass transport to microelectrodes (B6) . They gave a numerical solution procedure for calculation of the surface flux that is applicable to the general case of an arbitrarily shaped planar electrode, including both surface and bulk catalytic regeneration reactions. Multidimensional integral equations were used in another mathematically sophisticated approach to UME diffusion problems (B7, B8). The approach was stated to have considerable advantage over the conceptually simpler finite difference and finite element digital simulations in terms of computer requirements and execution time. UME configurations considered were microdisks embedded in an insulating plane of infinite or finite extent, microbands, the SECM problem, and an array of inlaid planar electrodes of arbitrary shape.

Brodsky et al. presented closed-form solutions of the diffusion kinetic equation for individual or arrays of UMEs that were based on a “zero range approximation” (B9) . They achieved excellent agreement between calculated and experimental collection efficiencies using literature data. Conformal mapping procedures for the digital simulation of diffusion at a microdisk have been optimized and improved (BI0, SI]).


Oldham has also generalized his treatment of steady-state voltammetry in the absence of supporting electrolyte (SE) in two important papers (B12, B13). In the first, theory was developed for three classes of voltammograms: “sign-retention voltammograms”, where Ox and R have the same sign; “charge neutralization voltammograms”, where a neutral product is generated; and “sign reversal voltammograms”, where Ox and R have opposite signs. In the first two situations, plateaus will exist in the limiting current region, while in the latter the current was predicted to increase in a linear fashion with potential. For the charge reversal CVs, there is a marked dependence on trace amounts of supporting electrolyte (B12). The second paper gave steady-state voltammetry theory at a hemisphere UME for any degree of supporting electrolyte excess relative to the concentration of the reactant. Reversible, quasi-reversible, and irreversible i-E curves can be calculated from the equations given and representative examples of different cases are worked out. The criteria presented by Myland and Oldham should give theexperimentalist new tools for characterizing electrode reactions by variation of the SE concentration. The theory, however, is developed by assuming that there is no adsorption of Ox or Ron the electrode surface.

Myland and Oldham also derived the support ratio, [SEI/ [reactant], needed to ensure that thelimiting current is within 2% of iIim for infinite excess SE, and to ensure that E1p is likewise displaced by less than 1 mV. Convective mass transport at macroelectrodes, i.e., RDEs, may be treated in a way that exactly parallels the general theory of this paper with simple algebraic replacements (B13).

Two important papers address problems that will arise for so-called nanodes, electrodes with characteristic dimensions on the order of nanometers. Smith and White calculated i-E curves for very small electrodes based on a numerical solution of the Nernst-Planck and Poisson equations (814). They showed that the double-layer electrical field can markedly affect the currents, even in the presence of a large excess of SE and even for neutral reactants. Under conditions where the double layer and the depletion layer have similar dimensions, and where charge separation in the depletion region occurs due to ionic flux, the assumption of electroneutrality is not generally valid. Another possible artifact for very small electrodes is the problem of incomplete adhesion or cracks between the electrode surface and the insulating sheath. This can create a “lagoon” of electrolyte solution behind a pinhole. Oldham modeled this situation with a geometrically well-defined lagoon and solved Fick’s equation in elegant style (B15). The limiting currents, the time to reach steady state, and the kinetic parameters extracted from the CVs all are significantly altered. These lagooned electrodes, however, do behave as UMEs and can have some analytical virtues, e.g., more reversible behavior phenomeno- logically.

Several articles have considered coupled homogeneous chemical reactions at UMEs (B16-B21). The EC, EC’, ECE, and DISPl reaction schemes were incorporated into simple theory using a steady-state reaction/diffusion layer concept (817) . Bond et al. have applied UMEs for the determination of Eo’ values and kinetic parameters for a Cr carbonyl complex that participates in a square scheme (B22) . This paper also described a neat procedure for correction of the iR, drop

involving the simultaneous measurement of the difference current between electrolyte solution in the presence and absence of analyte.

Other miscellaneous applications include the chronoamperometric determination of the absolute concentration of a well-behaved electroactive species a t a microwire UME (B23) . The procedure rested on the Aoki equation, whereby the concentration is a function of the intercept and slope of the it112/area vs t ’ I 2 curve (and the electrode radius and n value). A procedure was given by Wikiel et al. for measurement of the stability constants of metal complexes by analysis of the anodic dissolution reaction of a metal UME operating in a normal pulsevoltammetry mode (824) . Pulse techniques applied to dissolving metal UMEs such as Cu render the entire voltammetric wave accessible due to the reduced iR drop and double-layer capacity of the UME (825) . A Monte Carlo method of modeling the random motion of particles was employed to simulate diffusion noise a t a UME (B26).

Experimental Aspects. Procedures for the fabrication of UMEs have been pretty well worked out in recent years. Nonetheless, useful tidbits can be gleaned by perusal of experimental sections of the myriad of articles on UME applications. The reader is to be warned that surveying the literature in this manner is hit and miss.

A careful study was carried out on methods to maximize the S / N ratio for the detection of dopamine using Nafion- coated carbon fiber UMEs (B27). Sources of noiseconsidered included Johnson noise from the feedback resistor in the current follower, waveform generator noise, line noise, and physiological noise in in vivo measurements. In this study dopamine was readily detected at a 100 nM concentration with a S/N ratio of 25 using fast-sweep voltammetry.

Reasonable CVs of dopamine were obtained using very small carbon fiber UMEs (overall dimensions of 400 nm) that had been insulated with a phenol-allylphenol copolymer (B28). A simple procedure of sealing UME carbon fibers or wires in polypropylene has been published (B29) . On-line iR, compensation was employed to perform CV at sweep rates up to 11 kV/s using 7-pm carbon fibers (830). Peng et al. have described fabrication and electrochemical activation of carbon fiber UMEs for the in vivo determination of neurotransmitters (B31).

Photolithographic methods were used to make carbon IDAs with 3-pm-wide fingers separated by 2 pm of Si3N4 insulation (B32). The carbon, which was vapor deposited by pyrolysis of a perylenetetracarboxylic dianhydride, exhibited an electrochemical behavior similar to that of glassy carbon. Wrighton’s group, which has pioneered the use of photo- lithography to make UME arrays, has used surface spectroscopy to characterize an array consisting of six or eight individually addressable Au or Pt UMEs on a Si3N4 substrate (B33).

The experimental details for carbon-based enzyme electrodes often involve state-of-the-art fabrication techniques. For example, amperometric enzyme electrodes were prepared using extremely thin (35-50 nm thick) carbon films prepared by the pyrolysis of spin-cast polyacrylonitrile (B34) . The enzymes were entrapped on the nanobands by electropolymerization of 1,2-diaminobenzene in the presence of the enzyme. Mention is also made of the elegant surface


modifications of carbon fiber UMEs by Kuhr and co-workers (B35, B36). Enzyme electrodes were made using TTF-TCNQ salt deposited in the recessed tips of 7-pm carbon-fiber UMEs. The conducting salt mediated the redox chemistry of fla- voenzymes attached to the surface via the glutaraldehyde method (837) .

Platinum and gold UMEs were prepared by the direct electroreduction of Au(II1) and Pt(IV/II) onto the tips of carbon fiber electrodes that had been coated with an insulating polymer (B38). Also, Ewing’s group has used Au ring UMEs prepared by electrodeposition of Au onto carbon rings (B39). A little paper on the measurement of k” values for the Fe(CN)63-/4- couple has some interesting details (B40). The presence of millimolar amounts of cyanide in 1 M KCl solution was found to stabilize the response. Pretreatment by either polishing with an alumina slurry containing KCN or by laser activation yielded k” values in the range of 0.5 cm/s.

Particulars were given for construction of UME arrays using Buckbee-Mears minigrids (B41). The epoxy-potted electrodes were polishable and had relatively regular spacings (which were the cross sections of the minigrid wires). The morphology of micropit arrays formed by electrochemical etching of carbon fiberlepoxy electrodes was characterized by bullet-shaped tips (B42) . A proof-of-principle submicrometer galvanic cell consisting of STM-deposited Cu and Ag pillars on a HOPG surface was demonstrated (B43). Atomic microscopy showed that the 70-nm cell discharged when immersed in a plating solution.

Martin and his troops have been busy making and characterizing arrays of metal cylinders deposited in the pores of alumina microporous template membranes. They have prepared recessed gold disk array electrodes, for example, with very deep 200-nm-diameter microholes (B44). In another study, they showed that the color of arrays of Au cylinders with nanometer dimensions could be changed by variation of the aspect ratio of the nanocylinders (B45). Properly prepared arrays were transparent in the infrared region (2000-4000 cm-I) (B46). Also, arrays of CdSe and CdTe microfibrils were fabricated in this manner (B47).

Iridium is known to be a good substrate for mercury electrodes. A nice application of anodic stripping square wave voltammetry employed an iridium substrate-based Hg UME where the Ir was etched to a radius of 5-10 pm prior to Hg deposition (B48) . Metal ions were determined without deoxygenation, without added SE, and without controlled stirring during the deposition step. The diffusion coefficient of T1” in T1 amalgams was determined by UME chronoamperometric methods (B49).

Applications. Even a cursory survey of the current literature reveals that UME methodology and theory have widened considerably the playing field of electroanalytical chemistry. Several accounts have described UME voltammetry in the absence, or at low ratios, of the SE to analyte concentration where agreement was sought with Oldham’s theory (B50). Drew et al. reported agreement for ratios greater than 0.1, but found that natural convection and the tendency of the generated ions to scavenge ions into the diffusion layer vitiated the theory (B51). For inorganic redox couples of varying charge and Elf2 values, Cooper et al. also reported anomalous behavior in several instances (B52). Lee and Anson

found that the electroreduction of Fe(CN)a3- at carbon and Pt UMEs was markedly suppressed in the complete absence of S E (B53). Reduction of this species, however, could be efficiently mediated by the positively charged M V W + couple. Comproportionation kinetics of the latter system were studied by steady-state voltammetry in solutions of low SE concentration (B54). In an interesting study, Cooper and Bond found adsorption of neutral cobaltocene and passivation of the electrode surface for the (Cp)2C0+/~f- system in CHsCN (B55). At UMEs this gave rise to stochastic processes at negative potentials where cathodic dissolution of the film, as (Cp)2-, is possible.

Homogeneous electron-transfer kinetics in monomeric organic liquids such as nitrobenzene were studied by Norten et al. (B56). At Pt UMEs, the second wave for the formation of the NB2- dianion was depressed relative the first wave due to the combined effects of the comproportionation reaction and electrostatic repulsion of the NB’- away from the negatively charged depletion layer surrounding the electrode. Others have looked at the UME voltammetry of nitrobenzenes in low ionic strength aprotic media (B57), and Ciszkowska and Stojek obtained well-defined anodic waves, with a 0.5 n value, for the oxidation of solvent in neat alcohol solution with LiC104 SE (B58).

Several studies have employed UMEs at low or wide temperature ranges. Attention is drawn to the low-temperature CVs of the (Cp)2M2+f+f0/-f2- cobaltocene and nickelocene systems in liquid SO2 (B59), the careful kinetic study of the ferrocene couple over the 200-300 K temperature range (BbO), and the temperature-dependent phase transitions and diffusive electron and solute transport seen in polyether “solid-state” solvents (B61) . CVs of the Fe3+f2+ couple in ice featured surface or thin-layer behavior, indicating the existence of liquid water microphases in contact with the UME surface at temperatures below the freezing point (B62). Modestly fast CVs and chronoamperometry of polyaniline films in contact with HC10~5.5HzO at temperatures down to 220 K suggested that the oxidation process involved electrocrystallization phenomena (B63).

Voltammetry and chronoamperometry has been performed at pressures up to 8000 bar using Pt microcylinder wire electrodes (B64, B65). A two-electrode cell with a UME coated with redox polymer/enzyme functioned remarkably well in a CO2-based fluid near its critical point (B66).

Several more strictly analytical applications of UMEs included studies of the reduction of acids in the presence and absence of S E (B67, B68), ASV of heavy metals in natural waters at Hg UMEs (B69), and a method for thedetermination of the total acidity of various wines (B70). Good results were obtained for analysis of Hg in the absence of S E by ex situ plating of a UME Pt disk followed by transfer of the electrode to an electrolyte solution for ASV (B71). Very nice CVs of solid-state vanadyl sulfate hydrate were obtained at a carbon disk UME (B72).

UME voltammetry was carried out in a single drop of solution by Unwin and Bard, who measured the adsorption and ion exchange of H+ on a silicate mineral surface and of methylene blue on HOPG and polycrystalline graphite surfaces (B73). Likewise, Bowyer et al. did electrochemistry involumes as small as 0.05 pL using a three-band array consisting of a

Analytical Chemistty, Vol. 66, No. 12, June 15, 1994 365R

4-pm Pt working electrode, a 100-pm Ag reference electrode, and a 100-pm Pt counter electrode separated by heat-sealing film (B74).

In continuing publications, mostly from the Texas laboratory of Bard and co-workers, the versatility of the scanning electrochemical microscopy (SECM) technique has been demonstrated. Wipf and Bard made significant improvement in the technique by employing small-amplitude tip-position modulation in combination with lock-in detection of the signal (B75) . This gave unambiguous indication of whether a surface was conducting or insulating and markedly improved the contrast between those surfaces. In another study, it was shown that information on the tip shape could be obtained from the SECM response at a well-defined flat surface (B76) . This is important for very small UMEs where conical-shaped electrodes are much more easily fabricated than insulated UME disks. SECM theory was developed for the determination of fast heterogeneous kinetics from steady-state currents (B77, B78). The method, which involves determining the current as a function of potential for fixed values of d/a , where d is the separation between the scanning tip of radius a and the conductive surface, should permit rate constants up to 10-20 cm/s to be measured. The technique was applied to the measurement of the rate constants for the ferrocene+/O and C& couples (B78, B79). Also SECM, operating in the feedbackand generation/collection modes, was applied to the measurement of rates of chemical reactions coupled to electron- transfer steps for the electrodimerization of activated olefins (B80). Simulation of the redox kinetics in the tipsubstrate gap was performed in conjunction with SECM to image the redox enzyme glucose oxidase immobilized on nonconducting substrates such as nylon, hydrogel membranes, or a L-B film (B81).

An antimony UME was used with the SECM apparatus as a potentiometric sensor for hydrogen ion activity (B82). General theory was developed and applied to give pH images around a Pt electrode during the reduction of water, a corroding AgI disk in cyanide solution, a disk of immobilized urease hydrolyzing urea, and other systems. The SECM technique was used to characterize solid films of AgBr (B83). The diffusion coefficient of bromide ion in the AgBr matrix was deduced from the tip current transients produced when the tip/substrate pair was pulsed in a thin-layer electrochemical mode. SECM has also been employed to map ionic fluxes of electroactive species at various porous membranes including mica and mouse skins (B84) , to detect proton motion at polyaniline film electrodes (B85), to monitor ion release from protonated poly(viny1pyridine) films (B86), and to characterize a 200-nm-thick polymer film (B87). Surface diffusion and desorption processes are readily handled by SECM. In this application, the probing tip, biased at a potential where the adsorbate is electroactive, yields a current that is a function of the rate of diffusion through solution, the adsorption/ desorption kinetics, and the rate of surface diffusion (B88). The approach was illustrated by detection of H+ads at rutile- (001) and aluminosilicate surfaces.

In vivo electrochemistry under physiological conditions, which was the original motivation for UME voltammetry, has provided some of the most impressive applications of UMEs in analytical chemistry. The detection of the release of

catecholamines at the femtomole level from individual adrenal medullary chromaffin cells continues this tradition (B89). Interestingly, both cells that released only epinephrine and cells that released a mixture of epinephrine and norepinephrine were identified. Wightman’s group have used UMEs to monitor the flux of catecholamines from other biological cells during exocytosis (B90). The process was analyzed in terms of diffusive mass transport from a point source. Ewing’sgroup has used platinized carbon microring electrodes to monitor 0 2 concentrations and to perform multiple pulsevoltammetry in single neuron cells of their favorite pond snails (B91, B92). Oxidation currents have also been measured due to generation of superoxide anions at a carbon UME in contact with a single biological cell (B93) , and a Pt on graphite UME was used to monitor oxygen efflux from illuminated algae protoplasts (B94) . The release of NO from a single cell was detected with a carbon fiber UME coated with a polymeric porphyrin/ Nafion composite film (B95). Adams and co-workers used Nafion-coated carbon fibers to detect norepinephrine release and to profile glutamate-evoked ascorbic acid release in the brains of freely moving rats (B96, B97). Impedance analysis of 100-pm Pt electrodes covered with biological cell cultures indicated the formation of pores in the cell membranes upon application of small applied voltages (B98) .

UME arrays have been employed in innovative fashion. Electrochemical luminescence, generated by a radical cation plus radical anion annihilation reaction, was examined at double-band UME arrays both experimentally and theoretically using conformal mapping transformations (B99) . For reversible systems the depletion effect in differential pulse voltammetry is minimized for an interdigitated array (IDA) working electrode operating in the feedback mode (BIOO). An IDA electrode, also operating in the collection mode, was shown to be a sensitive detector under conditions compatible with an enzyme immunoassay (BIOI) . Volumes as small as 800 nL were successfully handled in this study. A clever application of an IDA incorporated an electrochemical coulometer in series with an IDA in a solution of a reversible redox couple. The coulometric process employed was electrodeposition of a metal, which was followed by ASV analysis allowing determination of the redox couple at the M level (B102). IDAs have been used to measure apparent electron diffusion coefficients in polymeric matrices: good examples are the study by Nishihara et al. of poly(ethy1eneoxide) (8103) and the redox switching of poly(pyrro1e) films (B104).

Several papers have addressed theoretical aspects of various array geometries. These include a treatment of the overlap of diffusion layers at microband arrays (B105), cylinder arrays closely aligned parallel to a planar electrode (B106), and dual- cylinder UMEs in parallel operating in a biamperometric mode with a small imposed voltage difference (B107). The latter theory was applied to the titration of ascorbic acid with ferricyanide.

Frequencies as high as 20-30 kHz were used for the generation of electrochemical luminescence by square-wave generation of the radical ions at UMEs (B108). A lower limit on the ion-annihilation rate constant for diphenylanthracene of 2 X 1 O9 M-’ s-l was determined. Double-band UME arrays have also been used to generate ECL in a steady-state mode of operation (B109).


Hydrodynamic Methods. Rotated Electrodes. Verbrugge has given a theoretical analysis of the RDE convective diffusion problem for an Ox/R couple that is valid for a wide range of Schmidt numbers and Reynoldsnumbers (BIIO). Thecurrent response was found to be bounded by the Levich equation for large Schmidt and Reynolds numbers and by the stationary disk response for zero Schmidt or Reynolds numbers. Vieil developed a general mathematical treatment of mass transfer that quantifies the transition between stationary convective mass transport and time-dependent accumulation at an electrode surface (BI 11). A mass-transfer rate expression is given that can accommodate a variety of experimental conditions such as fractal geometries and transient behavior at RDEs. Simulation of transient diffusion and migration to a RDE during deposition of a metal film gave information on the current distribution, the effect of inert electrolyte, and the role of disk size (B112).

Bartlett and Eastwick-Field have written a particularly cogent analysis of limiting currents at a RDE for a generalized ECE reaction scheme (B113) .

The effect of rotation rate on UME array composite RDEs was studied using composite electrodes of gold and graphite particles embedded in Kel-F (BI 14). As expected, significant enhancement of true current density was seen at the array electrode in comparison to solid electrodes; Le., [(i/area),,,,,/ (i/area),,~id] > 1, where the active area is used to calculate the current density.

Several researchers have used rotation rate modulation techniques in various studies. The rotation rate step method of Blauch and Anson (B115) was applied to a silver electrode to determine the diffusion coefficients of electroinactive ligands (BI 16). Anodic 0-transfer reactions at several electrodes (Pt, Au, Pd, Ir, and glassy carbon) were studied using a current difference RDE method that diminished the contribution of 0 2 evolution to the observed response (BI 17). A key role for adsorbed hydroxyl radicals was deduced in this study. Engelhardt et al. have presented theory for hydrodynamic square-wave modulation of a rotating ring disk electrode (B118-B120). The method is useful when there are parallel reactions and the ring current of interest is masked by large background currents. In the experiments of Schwartz (B121), the rotation rate of a commercial RDE was modulated by a sinusoidal or by a square root waveform. Fourier transformation then gave the frequency response of the system in a single experiment. Hydrodynamic impedance has also been employed by Deslouis and Tribollet (B122).

Papers continue to be published that exploit the power of rotating electrodes in mechanistic studies. Rotating ring disk techniques were used to study the MV2+l+Io system (MV is methyl viologen) in aqueous solution, where surface blocking by adsorbed neutral species had to be taken into account (8123) . Likewise, Kokkinidis et al. found that electrodeposition of neutral benzyl viologen onto Pt or Hg proceeded by direct nucleation and 3-D growth under mass transport control (B124). Other studies include chronocoulometric measurement of adsorbed intermediates in the oxidation of iodide at a Pt RDE (B125), voltammetry of adsorbed intermediates in the HER (B126), the electrocatalytic oxidation of CN- at a glassy carbon RDE (B127), the mediated reduction of an alkyl halide (BI 28), the detection of the anaesthetic halothane

via oxidation of released B r a t the ring electrode (B129), and measurement of enhanced D values due to homogeneous electron exchange in the RDE voltammetry of Ru-EDTA- poly(viny1pyridine) complexes (B1 30).

On the more applied side, the photographic fixation process at a AgCl emulsion disk electrode was followed by monitoring the flux at a ring electrode (B131), and a novel RRDE method was described for the detection of COz expired in breath from a human subject (B132).

Compton and Brown have proposed a RDE method to monitor particle size in solution that is based on the enhancement of mass transport in the presence of suspended particles (B133). Others have studied mass-transfer enhancement in a dilute suspension of rotating particles under the influence of shear flow (B134), and Gabrielli et al. treated the ac impedance of fluidized-bed electrodes, both theoretically and experimentally for gold beads in NaOH solution (B135).

In the miscellaneous category are papers on the rotating ring cone electrode (B136), mass transfer at the entire surface of a vertical cylinder electrode (B137), the use of an inverted RDE for the study of gas-evolving reactions (B138), and mass transfer at a RDE with external forced convection (B139).

Wall Jet and Channel Electrodes. R. G. Compton and his colleagues have continued their sophisticated analysis of wall jet and channel electrodes. As will be noted below in the section on electrochemical detectors for FIA or chromatographic columns, these configurations have real practical significance.

The Compton group has presented theory for the transient current response for a simple E step at a WJE (B140) and at the ring in a wall jet ring disk electrode (8141) . The theory was experimentally verified in a later study (B142). They also developed theory for CV at a WJE where the electrode is substantially larger than the jet. The theory predicts transitions from steady-state CVs at slow sweep rates to peak- shaped response at fast sweep rates (B143). The roleof radial diffusion in the WJE response has been considered in a more recent paper (B144).

Compton et al. have presented a general computational approach to calculation of i-E curves at channel electrodes (B145) and, in a related paper, calculated limiting currents for UME band electrodes in a rectangular flow channel under conditions where convection is the predominant mode of mass transport (B146). Tait et al. have also tackled the difficult problem of a UME disk electrode in a flow channel using finite difference simulation (B147). The effect of electrode size, solution velocity, and channel thickness on the magnitude of the near-steady-state currents and the time required to reach this condition were determined in the latter paper. A treatment of the catalytic EC’ reaction at a flow channel electrode is representative of several articles on coupled chemical reactions under these conditions (B148).

A four-element carbon paste array detector, which consisted of different graphite/metal oxide composite surfaces in a wall jet configuration, displayed different electrocatalytic sensitivities toward carbohydrates and amino acids (B149). In another study, the performance of an array WJE assembly was optimized (B150).

Flow- Through Electrochemical Detectors. Electrochemi- cal detectors for chromatographic or FIA columns (LCEC)


are routinely employed. Only a fraction of the recent papers that present possible advancements in the methodology will be cited here.

The WJE configuration is wellsuited to theLCEC problem. Stojanovic et al. evaluated cylindrical wire, thin-layer, and WJEdetectors with constant and pulsed amperometric (PAD) modes of operation for the determination of inorganic arsenic (B151) . In their hands, the WJE had the best LOD. Other recent examples of WJE LCEC detection can be mentioned (B152, B153). It can be noted, however, that the impressive sensitivity of carbon-fiber detectors, which has been exploited in the determination of catecholamines in single bovine adrenomedullary cells (B154), is difficult to match.

Electrochemical detection has been applied to capillary electrophoresis with much success. Sloss and Ewing, for example, have improved their methods by enlarging the end of the capillary to accommodate a larger UME. Problems with variation of the capillary/electrode alignment were also minimized with their new design, which gave detection limits as low as 11 amol for catechol (B155). Lunte and co-workers have given details on the construction of a complete capillary electrophoresis system with electrochemical detection (B156). They found that a 50-pm-diameter Au(Hg) amalgam UME functioned well as a C E detector for free thiols (B157). Lu and Cassidy evaluated several UMEs in a WJE configuration as detectors for capillary electrophoresis columns. Not unexpectedly, mercury amalgam electrodes gave the best performance for 14 test metal ions (8158) and PAD at a Au UME worked well on the anodic side (B159).

Mahoney et al. modified a commercial stationary mercury drop electrode apparatus so that square-wave voltammograms could be obtained under stopped-flow conditions (B160). Rapid-scan voltammetry at a UME detector was shown to give theoretical steady-state CVs under chromatographic conditions (B161). Trade-offs in sweep rate, UME diameter, and flow rate were evaluated.

Two groups have put 16-element LCEC amperometric detectors to good use. In the study of Sparks and Geng, detection over a potential window of 0.75 V greatly increased the information content of a single chromatogram (B162). In the impressive work of Aoki et al., 80-channel detection was achieved by application of a five-step E-staircase waveform with 1 0-mV step heights to the 1 6 elements oft he array (8163). IDAs operated in the dual-electrode mode were shown to have good sensitivities as flow detectors: 100 pM dopamine was detected under HPLC conditions (B164). An advantage of this mode of detection is that the component of the current due to redox cycling is flow rate independent.

Descriptions of several novel spectroelectrochemical flow detectors have appeared. Brown et al. used anodic photo- currents at Ti02 to detect species with redox potentials more negative than the valence band edge of the semiconductor at the 100-pmol concentration level (B165). Another flow cell was based on indirect detection of eluents by the decrease in the intensity of electrogenerated luminol chemiluminescence (B166). Also, a pulsed flash photolysis amperometric detector was described that appears to have some promise as a general purpose LCEC detector (B167).

Several papers have proposed various surface modifications to improve LCEC response. The dual-electrode sensor of

Doherty et al., which is based on redox polymer-modified electrodes, nicely performs speciation analysis of Fe(I1) and Fe(II1) (B168). One electrode was coated with a Ru-bpy polymer (E1p = 0.75 V vs SCE), which mediated the oxidation of Fe(II), and the other was coated with an Os-bpy polymer (E1p = 0.25 Vvs SCE), which mediated the Fe(II1) reduction. The latter electrode was also used for the FIA of nitrite ion with excellent sensitivity and stability of response (B169). Wang et al. employed self-assembled monolayers (SAMs) of n-alkanethiols on Au electrodes to vary the response of LCEC detectors to analytes such as chlorpromazine in urine samples (BZ 70). The SAM-modified electrodes discriminated against small ionic electroactive species and were stable under the hydrodynamic conditions of the flow cells. Mark and colleagues (B171), and others (B172), have found that conducting polymer film electrodes show improved performance in terms of sensitivity and antifouling properties for the detection of ionic species.

Numerous examples of chromatographic analyses employing electrochemical detection can be found in the forests of chromatography literature. Examples of pulse amperometric detection include a study of the sulfur compounds cysteine, cystine, methionine, and glutathione, all of which were detected in human blood samples using simple LC PAD procedures (8173) . PAD and HPLC/MS were employed in complementary fashion for the analysis of aminoglyoside antibiotics (B174); SO2 has been analyzed in beer by IC with PAD detection (B175); and HPLC of amino acids using PAD had excellent sensitivity and required little to no sample preparation (BI 76) . Johnson and co-workers have published two papers refining their PAD methodology. In one, pulsed voltammetry at a RDE was used to optimize the potential and time parameters for the PAD waveforms (B177), and the second gives construction details for a simple low-cost LCEC detector employing a gold working electrode (B178).

Other examples of LCEC that caught your reviewer’s eye were a fast-scan voltammetric detection of fullerenes (BI 79) , detection of underivatized polypeptides using constant potential amperometry (B180), and the coulometric detection of neurotransmitters and respiratory metabolites in brain tissue (B181).

Zhu and Curran considered porous flow-through amperometric detectors under conditions of low conversion efficiencies (B182). RVC electrodes were used to test the theory which predicted that the limiting currents were proportional to the 2 /3 power of the pore diameter. A UME biamperometric GC detector was evaluated (B183).

C. ANALYTICAL VOLTAMMETRY The year 1992 marked the 40th an-

niversary of the publication of the seminal article by Barker and Jenkins on square-wave polarography. This paper was reprinted by the Analyst in honor of the event (C1), along with a retrospective by Barker and Gardner (C2). The development of square-wave voltammetry (SWV), as well as other electroanalytical techniques, has continued over the past two years. For example, Chin et al. (C3) reported on the mathematicalenhancement ofSWV. Lovricet al. (C4) treated theoretically the use of SWV in cathodic stripping, while Komorsky-Lovric et al. (C5) looked at peakcurrent/frequency

Methodologies.

368R AnalyticalChemistry, Vol. 66, No. 12, June 15, 1994

relationships in adsorptive stripping. The theory and experimental verification of pseudopolarography at the mercury hemisphere ultramicroelectrode was examined for use in anodic stripping voltammetry and metal speciation studies (C6). A reference element (internal standard) method was examined for the analysis of natural waters by stripping voltammetry (C7) .

As in the past review, adsorptive stripping voltammetry has been the most dominant approach that has been reported. Jin et al. (C8) studied the amount adsorbed in the adsorptive accumulation at a symmetric spherical electrode in a stirred solution. Li, James, and Magee(C9) examined the effect of the accumulation potential in the adsorptive stripping voltammetry of organochlorine compounds. As will be seen below, the analysis of metals by an adsorbed metal complex has been quite productive. The induced reactant adsorption in pulse polarography was examined by Puy et al. in a series ofarticles ( C I e C 1 2 ) . Jin et al. (C13) compared conventional and derivative measuring techniques for linear potential sweep adsorption stripping voltammetry.

The scope and selectivity of adsorptive stripping voltammetry has been greatly extended by the use of complexing agents either in solution or attached to the electrode. This has enabled adsorptive stripping voltammetry to beextended to a wide range of metals. Carbon paste electrodes are excellent candidates in that a wide variety of reagents can be incorporated into the paste. For example, the incorporation of salicylideneamino-2-thiophenol allowed for the accumulation and adsorptivestripping of copper (C14). A functionalized silica gel was incorporated into carbon paste for the adsorptive stripping of mercury(I1) (C15). Mercury (C16) and thallium (C17) were concentrated with anion exchangers which were present in the carbon paste. A diphenylcarbazide-modified carbon paste electrode was used for the determination of chromium(V1) and chromium(II1) (C18) . Gold was selectively extracted with triisooctylamine- modified carbon paste (C19) or with thiobenzanilide (C20) . A long alkyl chain amine was used for the selective determination of pyridoxal in nonfat dry milk (C21) . A moss- modified carbon paste electrode was found to efficiently bioaccumulate lead (C22) . Organic cations such as paraquat were determined by adsorptive stripping voltammetry with Amberlite resin in carbon paste electrodes (C23) or an ion pair at a hanging mercury drop electrode (C24). Silica- modified carbon paste electrodes were used for the determination of todralazine in biological fluids (C25). OV-17 silicone-modified carbon paste electrodes selectively concentrated organic compounds such as benomyl prior to analysis (C26) . A diphenyl ether graphite paste electrode was used in the analysis of vanillin (C27) . While carbon paste has been the most popular electrode material, other electrodes have been derivatized or modified in some manner so as to provide for preconcentration prior to the stripping analysis. Nafion mercury film-modified electrodes were used for the anodic stripping voltammetry of bismuth (C28). A glassy carbon electrode coated with a Nafion film was used to preconcentrate a nitrosoamine ((229). Gold(II1) was determined by anodic stripping voltammetry using a glassy carbon electrode with an aza crown ether (C30).

Stripping Voltammetry.

While significant sensitivity and selectivity enhancement can be obtained by covalently bonding or mechanically entrapping an agent near the electrode, similar results can be obtained by forming strongly adsorbable complexes in solution. Some examples are the use of Beryllon I11 to form complexes with beryllium (C31) or copper (C32) prior to adsorptive stripping analysis. The same technique was used to determine aluminum (C33) or uranium (C34) with cupferron. Vanadium (C35) was determined by cathodic stripping voltammetry after deposition as the Solochrome Violet RS complex, while this same ligand can be used to determine aluminum by adsorptive stripping voltammetry (C36). Cathodic stripping voltammetry was used to determine tripeptides by the formation of the copper complex at a mercury electrode (C37, C38). Fulvic acid enhanced the adsorption of the Mo(V1)-phenanthroline complex in cathodic stripping analysis (C39).

A wide variety of organic compounds can be adsorbed on electrode surfaces and are ideal candidates for adsorptive stripping voltammetry. This is especially true of pharmaceutical compounds. Some examples of the drugs, electroanalytical techniques, and sample matrices that have been examined in the past two years are summarized below in order to give the reader a flavor for the scope of the technique. Villar et al. (C40) determined mitoxantrone using phase- selective ac adsorptive stripping voltammetry in a flow system. Phase-selective ac adsorptive stripping voltammetry was also used in the analysis of folic acid on a mercury thin-film electrode (C41) and aminopterin on a mercury thin-filmcarbon fiber microelectrode (C42) . Mercury-coated carbon fiber microelectrodes were also used in the adsorptive stripping voltammetry of folic acid and mitoxantrone (C43). Fluni- trazepam (a psychotropic drug) (C44) and lormetazepam (C11) were determined in urine by adsorptive stripping. Ranitidine in stomach tissue was determined by the same technique (C45), as was metronidazole in human serum (C46). Cholesterol (C47) in blood serum and testosterone propionate in pharmaceutical preparations (C48) was determined following adsorptive preconcentration. Multispecies analysis was obtained for the determination of riboflavin and folic acid in multivitamin preparations (C49) and nickel(I1) and cobalt- (11) on a rotating disk mercury film electrode (C50). Economou and Fielden (C51), though, investigated the effect of surfactants on adsorptive stripping voltammetry and found that interferences can occur on the milligram per liter level. They examined the use of fumed silica gel and Nafion films to alleviate these problems.

A more forceful way of applying the sample to the surface was utilized in abrasive stripping voltammetry, where the sample is physically deposited unto the surface. Komorsky- Lovric et al. compared the use of electrochemical and abrasive deposition onto a paraffin-impregnated graphite electrode for the analysis of lead and mercury (C52). Scholz et al. (C53) examined the anodic dissolution of dental amalgams by abrasive stripping voltammetry. This same stripping technique was also used to study the thermodynamics of solid-phase transitions (C54).

There were several reports over the past two years on the use of new electrodes for anodic stripping voltammetry. Mercury films on conducting poly(3-methylthiophene) (C55) or poly-N-ethyltyramine (C56) on carbon surfaces were

Analytical Chemistty, Voi. 66, No. 12, June 15, 1994 389R

reported. Wang et al. investigated the use of mercury-coated carbon foam composite electrodes (C57), vitreous carbon aerogel electrodes (C58), and screen-printed stripping electrodes (C59). Frenzel (C60) discussed the attributes and problems of using mercury films on a glassy carbon support. Ultramicroelectrodes have also been applied to anodic stripping analysis. A mercury ultramicroelectrode electrode was used by Peng and Jin (C61) to determine lead in a sample-limited analysis (e.g., 1 mg of hair). Gold fiber microelectrodes were used to determine mercury in high-purity gallium arsenide (C62) or waters and fertilizers (C63), mushrooms (C64), and selenium( IV) in blood serum (C65) . Copper (C66) and lead/ cadmium (C67) were determined in the absence or presence of low concentrations of supporting electrolyte. Kouvanes and Deng (C68) examined the use of an iridium-based mercury ultramicroelectrode with square-wave anodic stripping voltammetry.

The effectiveness of various methods to remove interferences in anodic stripping voltammetry was examined. The influence of complexing agents on the effectiveness of electrochemical masking with anionic surfactants was examined by Opydo (C69). The detection of Ga-Zn interme- tallic compounds and its removal with antimony was reported by Cofre and Brinck (C70). Surfactants were used to suppress the indium peak in the determination of lead in samples that contained large concentrations of indium (C71). A photochemical process was reported by Barisci and Wallace (C72) for the removal of oxygen in flowing solutions. Photochemistry was also used in sample preparation of heavy metals in peat (C73), while a digestion method for soil samples was reported by Fernando and Plambeck (C74). Systematic errors due to adsorption of metal complexes onto cell components were investigated (C75). Sodium and other impurities in alkoxy- silanes were determined by anodic stripping square-wave voltammetry (C76) .

Metals are generally the most likely candidates for determination by anodic stripping voltammetry, but there are several reports on the determination of organic compounds, either directly or indirectly. Cholesterol in blood serum was found to be amenable to anodic stripping voltammetry (C77), as were ionic alkyllead compounds in natural waters (C78) . An indirect method for the analysis of NTA and EDTA in natural water by means of a bismuth complex was reported

The bulk of the reports on cathodic stripping voltammetry has involved the determination of halides and chalcogens. For example, total inorganic iodine in seawater (C80) or a variety of sulfur species such as thiols, sulfides, cysteine, and cystine (C81) were also determined. Wang and Lu (C82) reported on the ultratrace measurement of selenium in the presence of rhodium. A mercury-coated carbon-fiber electrode was used for the determination of selenium(1V) in blood serum (C83). Smyth et al. (C84) reported on the determination of organic and inorganic selenium compounds, while Kotoucek et al. (C85) determined arsenic. Organic compounds such as cytosine 3’-phosphate (C86), thiamine (C87), pentamidine isethionate (C88), and glutathione in natural waters (C89) were amenable to cathodic stripping voltammetry. The adsorption of “reduced COZ” on platinum was the basis of a new technique for the determination of carbon dioxide (C90).

(C79) *

Wang and Tian (C91) developed a mercury-free disposal lead sensor based on potentiometric stripping voltammetry using gold-coated screen-printed electrodes. Xie and Huber (C92) used constant-current enhanced potentiometric stripping voltammetry for the analysis of cadmium. Potentiometric stripping voltammetric techniques were also developed for the determination of cadmium and lead in whole blood (C93), copper and lead in tap water (C94), and manganese (C95). Komorsky-Lovric and Branica (C96) compared potentiometric stripping voltammetry and square-wave voltammetry with respect to the influence of Triton X- 100. Aldstadt and Dewald (C97) studied the effect of model organic compounds on potentiometric stripping voltammetry with a cellulose acetate membrane covered electrode.

Catalytic Methods. The combination of preconcentration of the analyte in stripping analysis and enhancement of the signal by use of a catalytic reaction (dual amplification) provides for a very attractive approach to develop extremely sensitive electroanalytical methods. Some examples of this methodology have been recently reported. One elegant approach is to use a complexing agent that is, itself, an oxidizing or reducing agent in the stripping step. This technique was used in the analysis of chromium (C98), molybdenum (C99), and thorium (C100) using cupferron as the ligand for adsorptive stripping voltammetry as well as the catalytic oxidizer in the stripping step. In addition to cupferron, organic hydroxy acids (CIOI) and chlorate (mandelate as the ligand) (C102) were used to determine molybdenum. Iron in seawater was determined by cathodic stripping with 2-nitroso-2- naphthol and the use of hydrogen peroxide as the oxidizing agent in the stripping step (C10.3). Bobrowski and Bond (C104) combined adsorptive stripping voltammetry of a cobalt complex with the catalytic effect of nitrite on the stripping wave to enhance the sensitivity of the cobalt analysis. The catalytic reaction, alone, without prior accumulation, was used by Hsieh and Ong to determine molybdenum by differential pulse polarography (C105), and by Jiang et al. (C106) to determine nitrite.

Derivatization Methods. The efficient conversion of electroinactive compounds to eiectroactive materials or to change the redox potential of electroactive materials can be exploited to develop new electroanalytical methods. For example, reactive organic halides can be determined at low levels via in situ generation of S-alkylisothiouronium salts (C107) with differential pulse polarography. Similarly, ethanol (CI08), amines (CI09) , and amino acids (CIIO) can be determined via in situ generation of dithiocarbamates. Oxalate can be determined by differential pulse polarography after derivatization with o-phenylenediamine (C1 1 I ) . Sul- fanilic acid was converted into an azo compound prior to differential pulse polarographic measurement (CI 12). Somer and Kocak developed a method for the differential pulse polarographic determination of sulfur dioxide using selenite (C113). The reaction of ammonia with formaldehyde was used as the basis for the analysis of ammonia in seawater (CI 14) . The formation of nickel complexes with ampicillin and amoxycillin led to a selective differential pulse polarographic method (CI15).

Analytical Use of Micelles. Micellar and emulsified media provide an efficient method for solubilization and transport


of the analyte to the electrode surface. Emulsified media were used to determine pesticides by differential pulse polarography (CI 1 6 4 1 18). The combination of micellar media and a surfactant-modified carbon paste electrode was used for the adsorptive stripping analysis of piroxicam (C119). Zinc in lubricating oils was determined in emulsified media (C120).

Pulse and Sweep Methods. While prior accumulation of analyte can greatly lower the limit of detection, such sensitivity is often not required, and an accurate, direct method is appropriate. In this section, recent applications of direct voltammetric analysis will be reviewed. A number of articles addressed themselves to the determination of acidity in a variety of matrices. For example, steady-state voltammetry of simple and polyelectrolyte strong acids, as well as weak acids, with and without supporting electrolyte was examined (C121, C122). Ultramicroelectrodes were used to determine the total acidity in wines (C123) and the "in situ" acid number of fluid lubricants (phosphate esters) (C124). An ultra- microdisk electrode was used for the solid-state electroanalysis of silicotungstic acid single crystals (C125). The determination of elemental sulfur and sulfide was obtained by the use of ac voltammetry (CZ 26).

Many examples of the use of differential pulse voltammetry to measure a substrate or impurity were reported. For example, furaltadone (CI 27) in milk and urine was determined by differential pulse polarography. Trace levels of selenium in Chinese herbal drugs (CI 28) and total pyrethroid residues in stored cereals (CI 29) were determined by differential pulse polarography. Impurities in several pharmaceutical preparations were determined by differential pulse polarography (C130, C131). Pulse methods were also found to be useful in the analysis of solid materials such as the determination of iron in Y Ba2(Cul,Fex)30, superconducting compounds (CI 32) or the analysis of additives such as iron, sulfur, or chromium oxide in soda lime silica glass (C133). The oxygen-to-uranium ratio in uranium dioxide was determined by differential pulse polarography (CI 34). A lichen-modified carbon paste electrode was found to be useful for the analysis of lead, copper, and mercury (C135).

Mathematical methods to enhance the signal and resolution have been applied to various pulse techniques. The Kalman filter approach was used for curve resolution and quantification of pyrazines by differential pulse polarography (C136). Reverse differential pulse voltammetry was used by Matysik et al. (C137) to improve the resolution between various catechols such as norepinephrine and 3,4-dihydroxyphenylacetic acid. Engblom et al. (C138) studied mechanically generated noise in static mercury drop electrodes.

Metal/Ligand Complexation Studies. The complexing ability of natural waters can significantly affect the bioavail- ability of metals. Electrochemical methods are ideal to probe these effects and give them a significant advantage over atomic methods. The derivation and application of steady-state (C139) or normal pulse (C140) voltammetry for the determination of formation constants were examined. An anodic stripping voltammetry titration technique was developed for estimating the complexation capacity of natural waters (C141). Anion coordination chemistry was studied by the application of the molar ratio method to competitive cyclic voltammetry

(C142). Esteban and Diaz-Cruz (C143) reported on a general voltammetric method for studying metal complexation in macromolecular systems. Zelic and Branica (C144) examined the influence of anion-induced adsorption on the voltammetric determination of stability constants. Van den Berg and Donat (C145) found that there was a linear relationship between the detection windows of the analytical techniques and the detected metal complexation. They investigated the effect of multiple ligands on speciation studies as well as the presence of slow metal/ligand dissociation kinetics. The effect of deposition potential on the voltammetric determination of complexing ligand concentrations in seawater was also examined (C146).

Equilibria that involved metal-humate complexes, as models for natural water and seawater studies, were examined using anodic stripping voltammetry. A modified carbon paste electrode was reported for the study of the metal humic complexation reaction (C147). A procedure for metal speciation studies in the natural environment was reported which involved ultrafiltration of the sample and the study of the complexation dissociation kinetics using anodic stripping voltammetry and ion exchange (C148). This approach allowed the study of dissociation kinetics that could be varied between 2 ms to 8 days. The effect of competitive kinetics between a solution copper complex and an iminodiacetate group, which was incorporated into a carbon paste electrode, was the basis for a copper speciation analysis (C149). A solution ligand competition technique was proposed for the voltammetric measurement of the labile metal fraction (C150). The basis of this technique is that the natural copper complex dissociates too slowly for the copper to be deposited while the ethylene- diamine complex is labile and can be detected by anodic stripping voltammetry. The effect of sodium dodecyl sulfate on the measurement of labile copper(I1) in the presence of humic acid was examined (CIS]).

Chemometric Approaches. The chemometric approach to linear calibration was used by Allus and Brereton (C152) to determine thallium in cement dust and sediment samples using anodic stripping voltammetry. Ni et al. (C153) developed a method for the analysis of mixtures of pyrazines, which are flavor components of cocoa. The severe overlap of the peaks would preclude normal voltammetric analysis, but the use of chemometric methods with differential pulse voltammetry made it possible to carry out the analysis. An expert system for the determination of trace metals was reported by Esteban et al. (C154, C155). The expert system guided the user through appropriate methods, data analysis, and interference problems.

D. HETEROGENEOUS/HOMOGENEOUS KINETICS Electron-Transfer Theories. The solution and molecular

factors that affect the electron-transfer process is a question of fundamental importance in electrochemistry and continues to be the focus of considerable research. Fawcett and Opallo (DJ) examined the question of why activation enthalpies for anions were larger than for cations. They proposed that the differences may be due to outer-sphere contributions to the Gibb's energy of activation. They also examined 18 heterogeneous redox reactions and found that the degree of dependence bfthe rate constant on the longitudinal relaxation time of the solvent decreases with the heterogeneous rate


constant ( 0 2 ) . The results were discussed in light of contemporary electron-transfer theory. Phelps et al. ( 0 3 ) studied solvent dynamical effects in electron transfer with a series of sesquibicyclic hydrazines as a probe of coupled vibrational activation. These systems provide an interesting opportunity to assess the manner and extent in which overdamped solvent relaxation may limit the electron-transfer dynamics. Fawcett and Fedurco ( 0 4 ) examined medium effects on the electroreduction of benzophenone in aprotic solvents. The solvation of the activated complex was based on three contiguous spheres corresponding to the two phenyl rings and the carbonyl group and was used to assess the outer- sphere contribution to the Gibb’s activation energy. It has been found that the heterogeneous electron-transfer rate constant decreased as the size of the tetraalkylammonium cation in the supporting electrolyte increased. But Fawcett et al. ( 0 5 ) found that the activation enthalpy was independent of the cation size and that the slow electron transfer was due to an adsorbed layer of cations at the electrode surface.

Pressure was used by Cruanes et al. ( 0 6 ) to study solute/ solvent interaction in electron-transfer processes. Increases in pressure (up to 10 kbar) led to shifts in the redox potentials which were attributed to the effect of the metal cluster’s electronic structure on the overall size of the complex and on its ability to interact with the solvent. Fawcett et al. ( 0 7 ) reported on the use of buckminsterfullerene as a model reactant for testing electron-transfer theories. McDermott et al. ( 0 8 ) examined electron-transfer kinetics of aquated iron, europium, and vanadium couples at carbon electrodes and found inner- sphere catalysis by surface oxides. Straus and Voth ( 0 9 ) presented a computer simulation study of free energy curves in heterogeneous electron transfer.

Dissociative electron-transfer reactions were studied extensively by Saveant and co-workers. As with the simpler heterogeneous electron-transfer reactions reported above, the role of the solvent was an important focus of these studies. The role of the solvent was examined by an ab initio study of the carbon halogen bond reductive cleavage in methyl and perfluoromethyl halides (010). New tests of the electron- transfer theory were examined using data derived from outer- sphere electron-transfer data gathered in the same solvent ( 0 1 1 ) . They also reported examples of passage from a sequential to a concerted mechanism in the electrochemical reductive cleavage of arylmethyl halides ( 0 1 2) . Jaworski et al. ( 0 1 3 ) used the Hammett reaction constant for the two- electron irreversible reductive cleavage of substituted chlo- robenzenes and bromobenzenes to show the role of solvent relaxation dynamics in irreversible electrode processes accompanied by bond cleavage. Concurrent metal-ligand bond dissociation was reported by Carlin et al. ( 0 1 4 ) to lead to asymmetric electrode kinetics.

Heterogeneous Kinetics. Methods to measure faster electron-transfer rates continue to be pursued. Karpinski and Osteryoung ( 0 1 5 ) used pulse times of 5 ps in normal and reverse pulse voltammetry to measure the electron-transfer rates of ferrocene (1.2 cm/s) and anthracene (0.73 cm/s) a t 5-pm platinum electrodes. Safford and Weaver ( 0 1 6 ) used lower temperatures to determine rate constants for rapid electrode reactions using microelectrode voltammetry. U1- tramicroelectrodes allow the charging current to decay rapidly,

and as a result, the voltammograms could be obtained with little of the charging current present. Lavagnini et al. ( 0 1 7 ) developed the theory for the measurement of electron-transfer rates under mixed spherical/semiinfinite linear diffusion at microdisk electrodes. Birke and Huang ( 0 1 8 ) investigated steady-state voltammetry for quasi-reversible heterogeneous electron transfer on a mercury oblate spheroidal microelectrode. Mirkin and Bard ( 0 1 9 ) presented a simpleanalysis of quasi-reversible steady-state voltammograms using the E1/4, E , / * , and E314 potentials. Kim et al. ( 0 2 0 ) examined the use of derivatives to analyze voltammograms for reversible, quasi- reversible, and irreversible electrode processes. Munoz et al. ( 0 2 1 ) found that electron-transfer processes with very low transfer coefficients led to a splitting of the differential pulse polarographic wave, even though there was only a single electron transfer. Engstrom et al. ( 0 2 2 ) used scanning electrochemical microscopy to observe microscopically local electron-transfer kinetics. Cassidy et al. ( 0 2 3 ) extended cyclic voltammetric theory to a quasi-reversible system with a Gaussian distribution of heterogeneous rate constants. Mirkin et al. ( 0 2 4 ) used scanning electrochemical microscopy to measure fast heterogeneous kinetics. The heterogeneous rate constant for ferrocene in acetonitrile, which was measured at steady state with solution resistance and charging current, was found to be 3.7 cm/s, 2-4 times the values determined by fast-scan cyclic voltammetry.

Accurate measurement of peak potentials and currents in transient signals are usually imperative in order to obtain good kinetics information. Andrieux et al. ( 0 2 5 ) examined methods to improve the kinetically relevant data in cyclic voltammetry and showed that filtering caused significant increases in systematic error which negated any advantage in the reduction of random error. Smith and White ( 0 2 6 ) cautioned that the use of ultramicroelectrodes with dimensions less than 0.1 pm will lead to violation of electroneutrality due to the high electric fields, even in the presence of excess supporting electrolytes. This can result in significantly enhanced or depressed values of the heterogeneous rate constant. Two reports, which take different approaches to the removal of iR drop in cyclic voltammetry, have appeared. Eichhorn et al. ( 0 2 7 ) used a numerical method to correct iR drop errors for (quasi-)reversible electrode processes, while Hsueh and Brajter-Toth ( 0 2 8 ) used on-line iR compensation at carbon fiber ultramicroelectrodes.

Homogeneous Kinetics. The development of much more efficient numerical methods for solving diffusion/kinetic problems has continued unabated. Most electrochemical mechanisms are a combination of several kinetic steps that must be considered if a complete fit of the data over a wide time window is to be attempted. This can only be accomplished by fast and accurate algorithms. Bieniasz (D29) proposed a dynamically adaptive grid technique for the solution of finite difference equations with a fast homogeneous reaction. While the approach is not entirely satisfactory at present, this strategy does permit the simulation of homogeneous rate constants that are as much as 20 orders of magnitude faster than the maximum possible in corresponding fixed-grid calculations with the same number of space grid points. Horno et al. ( 0 3 0 ) presented a network approach to the simulation of electrochemical processes where space was discretized but


time was continuous, This allowed a mathematical model to be described by a network model and its simulation could then be carried out by a suitable electric simulation routine without having to deal explicitly with thedifferential equations. Rudolph (031) reported an improved treatment of electrochemical mechanisms with second-order reactions using the fast implicit finite difference (FIFD) algorithm. Britz (032) incorporated the Crank-Nicolson scheme and N-point boundary expression into the Rudolph algorithm. Storzbach and Heinze (033) simulated electrode processes at macro- and microelectrodes using the Crank-Nicolson technique. The simulations included iR effects and double-layer capacitance as well as the heterogeneous/homogeneous reactions. Bieniasz and Britz (034) presented electrochemical simulations of mixed diffusion/ homogeneous reaction problems by the Saul’yev finite difference algorithm. They also compared the efficiency of electrochemical simulations by orthogonal collocation and finite difference methods (035). A very interesting and valuable report on the von Neumann stability of finite difference algorithm was published by Bieniasz (036). The stability of the explicit, second-order Runge-Kutta, DuFort-Frankel, fully implicit, Crank-Nicolson, and Saul’yev methods was examined. It was found that the stability depends notonlyon the DAt/h2 (A) factor but alsoon therateconstant. In examining the error growth as time goes to infinity, the criterion of h < 0.5 is insufficient for stability when homogeneous reaction kinetics are involved.

Mirkin and Bard (037, 038) used multidimensional integral equations to solve microelectrode diffusion problems with application to microband electrodes and scanning electrochemical microscopy. Second-order homogeneous chemical reactions were also studied by scanning electrochemical microscopy (039). Che and Dong published a series of papers on the theory for the use of ultramicroelectrodes to study first- and second-order homogeneous catalytic reactions (040-042). Lavagnini et al. (043) carried out the digital simulation of steady-state and non-steady-state voltammetric responses for electrochemical reactions occurring at an inlaid microdisk electrode. In this work, they examined the ECi, catalytic, and CE first-order reactions. Evans (044) examined the two-component diffusion (involving cyclodextrin equilibria) with reaction in chronoamperometry. Andrieux et al. (045) studied the response of an irreversible system to repetitive cyclic voltammetry. Maestre et al. (046) applied Matsuda’s pulse polarographic theory to the study of the CE mechanism by differential pulse polarography. Mellado et al. (047) derived the theory for electrochemical processes preceded by concurrent first-order chemical reactions in dc polarography. Laviron and Meunier-Prest (048) examined the cubic scheme with electrochemical reactions and proto- nations at equilibrium. Vincent and Peters (049) carried out the computer simulation of large-scale controlled-potential electrolysis involving father, son and grandfather, grandson self-protonation systems. Kumar and Birke (050) used global analysis of current/potential time data to study an EC reaction.

Bieniasz presented a PC program, ELSIM, which can simulate a variety of electrochemical mechanisms by finite difference or orthogonal collocation methods (051). A very attractive approach for the construction of digital simulation programs was reported where the equations which describe

the electrochemical kinetic initial and boundary value problems are treated as text input data for a special formula translator (052). The use of a knowledge-based system for automatic polarographic elucidation of the ECE, EE, and adsorption mechanisms was reported by Palys et al. (053).

Hydrodynamic methods are quite attractive for kinetics studies becauseone does not need to measure a transient signal. Compton et al. examined thin-layer effects and the shape of quasi-reversible current/voltage curve (054) and the catalytic mechanism (055, 056) for channel electrode voltammetry. It was also found that radial diffusion must be considered at the wall jet electrode in order to have a full quantitative description of the steady state or transient current (057). The authors reported that this additional computational complexity may limit this technique for use in kinetic studies. Benderskii and Mairanovskii (058) described numerical/analytical methods to study ECE processes at the rotating disk electrode. Daasbjerg (059) reported on a new method for studying the competition between coupling or further reduction of electrogenerated material using a rotating disk or ultramicroelectrode.

Double-Layer Studies. There was considerable interest in the electrical double layer that extended well beyond electroanalytical considerations. While beyond the scope of this review, there were many studies on electrical double layers at nonconducting surfaces, in colloids, and in chromatography. For electrochemists, an understanding of the electrical double layer is tightly connected to an understanding of the electron- transfer process, which occurs within that region. Murphy et al. (060) presented a numerical study of the equilibrium and nonequilibrium diffuse double layer applying the finite difference method to the Nernst-Planck and Poisson equations. Karasevskii et al. (061) developed a self-consistent theory of the metal/solvent boundary using a jellium model of the metal and a continuum solvent model. They found the existence of a quasi-metal layer in the near electrode region which provides a novel explanation of the large width (3-5 A) for the area of adiabatic reaction, the independence of the heterogeneous rate constant on the nature of the metal, and the capacitance properties of the boundary. Damaskin and Safonov (062) studied the mercury/water interface using a model which separates the diffusion layer region with a reduced value of the dielectric constant that is inaccessible for some electrolyte ions. Izotov and Kuznetsov (063) examined changes in the electron-transfer coefficient caused by the rearrangement of the compact double layer following changes in electrode potential. Hsu and Kuo (064) derived approximate analytical expressions for the properties of an electrical double layer with asymmetric electrolytes. Daghetti et al. (065) calculated single ion activities based on the electrical double-layer model. Hamelin et al. (066) tested the Gouy-Chapman theory at a (1 11) silver single crystal electrode.

Fawcett et al. examined the double layer in ethanolic solutions (067) and applied the ac admittance technique to double-layer studies on polycrystalline gold electrodes (068). Wandlowski and DeLevie (069-071) studied the double- layer dynamics in the adsorption of tetrabutylammonium ions at the mercury/water interface. Swietlow et al. (072) carried out double-layer capacitance measurements of self-assembled layers on gold electrodes. Studies on the structure of the


interphases of low melting point salts and protonic hydrates with mercury and gold ( 0 7 3 ) and solvent effects in the double- layer structure for gallium and gallium-like metals ( 0 7 4 ) were examined. Perez et al. ( 0 7 5 ) studied the Hg/aqueous KCl interface from ambient temperature to 300 OC. Bai et al. ( 0 7 6 ) investigated the problem of real-area determinations of rough or porous, gas-evolving electrodes and the distinction between capacitance of the double layer and the pseudo- capacitance due to adsorbed hydrogen. Jaworski and Mc- Creery studied double-layer and ion adsorption effects in laser- induced transient currents on glassy carbon electrodes ( 0 7 7 ) . Leibig and Halsey ( 0 7 8 , 0 7 9 ) used double-layer impedance as a probe of surface roughness.

Adsorption Studies. Because adsorption processes have a great impact on electron-transfer kinetics, double-layer structure, and electroanalytical techniques, efficient and reliable methods for studying adsorption have been pursued. Unwin and Bard ( 0 8 0 ) used ultramicroelectrode voltammetry to measure adsorption isotherms in a drop of solution. These authors also used scanning electrochemical microscope- induced desorption to measure adsorption/desorption kinetics and surface diffusion rates ( 0 8 1 ) . Three-dimensional phase- sensitive ac voltammetry was used to study the adsorption of sodium dodecyl sulfate at the mercury/electrolytic solution interface (082) . Gu et al. ( 0 8 3 ) used fast potential relaxation transients to distinguish between double-layer and adsorption capacitance.

Blankenborg et al. ( 0 8 4 ) examined the reduction of Tl(1) at a mercury surfaceand found that, for weak linear adsorption processes, it was impossible to distinguish between the direct reduction of TI(]) and the formation of an adsorbed Tl(1) intermediate. Avaca et al. ( 0 8 5 ) described the theory of cyclic voltammetry for quasi-reversible electrodeposition reactions with insoluble products. Tilak and Conway ( 0 8 6 ) determined the analytical relationships between reaction order and Tafel slope derivatives for electrocatalytic reactions involving chemisorbed intermediates. Song et al. ( 0 8 7 ) developed the theory for quasi-reversible electron-transfer reactions with adsorption of the redox species using integer and half-integer integrals. Jin et al. (088 , 0 8 9 ) examined the theory for an irreversible interfacial reaction in linear potential sweep adsorption voltammetry. The characterization of a totally irreversible reduction of an adsorbate ( 0 9 0 ) and quasi- reversible surface processes ( 0 9 1 ) by square-wave voltammetry was reported. Rouquette Sanchez and Picard ( 0 9 2 ) developed the theoretical expressions for the steady-state current/potential curves for the electrochemical oxidation of a metal involving two successive charge-transfer steps with adsorbed intermediate species. The role of surface defects in the adsorption and electron-transfer kinetics of anthraquinonedisulfonate on ordered graphite electrodes was reported by McDermott et al. ( 0 9 3 ) .

Engelman and Evans ( 0 9 4 ) used explicit finite-difference digital simulation of the effects of rate-controlled product adsorption or deposition in cyclic chronocoulometry. The simulation of Frumkin-type adsorption processes by orthogonal collocation using cyclic voltammetry was reported by Schulz and Speiser (095) . The experimental verification of theoretically predicted effects of reactant adsorption in normal pulse polarography was reported by Lukaszewski et al. ( 0 9 6 ) . The

semiintegral method was used to measure surface excess and weak adsorption (097 , 0 9 8 ) .

E. SURFACE ELECTROCHEMISTRY This section is organized by the nature of the working

electrode. The major theme of the articles selected for mention here is characterization of the electrode surfaces and the reactions of adsorbed species.

Theoretical Aspects. The articles cited in this section have a decidedly fundamental bent; it is noted, however, that important theory is often published in conjunction with experimental results, so this is not an exhaustive compilation.

Leiva carried out a self-consistent calculation of the electron density that included pseudopotentials to estimate the contribution of the metal to the double-layer capacity at thin metal films of Pb and Ag ( E l ) . Trasatti has analyzed the variation of the work function for single crystal Au and Ag electrodes as a function of the Epzc (E2) .

Wandlowski and de Levie (E3) invoked a two-dimensional surface cluster model to explain the admittance of "needle peaks" that are seen in Cdl-E curves for the Hg/H20 interface in solutions of tetrabutylammonium salts. Their theory took into account growth and dissolution of the surface clusters both at the perimeter edge and at the cluster/electrolyte interface. A similar model was used by Schrettenbrunner et al. in their analysis of film formation at the Hg/CH$N interface (E4) . Nikitas also treated micelle formation on electrode surfaces (E5) . H e predicted a close correlation between aggregate formation from a dilute solution of monomers and surface phase transformations that would result in abrupt steps in the charge density and cdl vs E curves. In previous papers, de Levie and co-workers considered the effect of the time-dependent relaxation of the diffusion layer on the value of Cdl when species aredesorbed from an electrode surface (E6) . Using digital simulation and assuming a Frumkin isotherm, they explained the transients quantitatively. In the case of a linear isotherm, they derived an explicit relation for the time dependence of the interfacial excess for various adsorption/desorption rate constants (E7) .

In several papers Nikitas has described surface phase transitions and adsorbate reorientations in statistical mechanical and thermodynamic rigor (E8-EI0). Among the conclusions of this work are that only irreversible phase transitionscan take place at constant chargedensity (E8) and that the diffuse layer capacity, and the capacity of the entire interface, cannot be negative if the electrical double layer is under potential control ( E l l ) . The use of the electrode potential as the independent variable is promoted and negative capacities are concluded to be a result of an incorrect choice of the independent variable. Increase in surface heterogeneity is predicted to disfavor surface phase transitions, an effect predicted on solid electrodes but not on mercury (E12) . Nikitas has also presented a thermodynamic treatment of the monolayer formation of a salt film on an electrode surface (E13) .

Monte Carlo statistical mechanical simulations of the free- energy profiles of sodium ions at a metal electrode have been made for water and T H F solutions ( E l 4 ) . In both solvents, a single, fairly deep minimum is found corresponding to the sodium ion with its first shell of solvent molecules in contact


with the electrode. Thus the O H P is predicted to reside about one solvent diameter closer to the electrode than in classical models, in which an adsorbed noncomplexed solvent layer is assumed to exist in the inner layer.

A theoretical analysis of molecular polarization and interactions in adsorbed monolayers permited calculation of isotherms for adatoms and for competitive adsorption of ions and dipoles ( E I 5 ) .

Several papers have concerned the ac impedance of surface reactions (El6-E18). These include an analysis of the impedance of an (Ox/R),ds couple for both planar and porous surfaces ( E l 6 ) and for the situation where two different adsorbed intermediates are involved in the electrode reaction ( E l 7 ) .

Scott has presented electrochemical rate equations for several reaction mechanisms involving adsorbed intermediates (E19). Rather than power law expressions, the rate is expressed in a “Langmuir” isotherm model in which the influence of electrode potential and concentration can be assessed separately. On a similar theme, Tilak and Conway derived relationships between reaction orders and Tafel slopes for electrocatalytic reactions involving adsorbed intermediates (E20) . Various adsorption isotherms were factored into their theory, which was applied to several experimental situations including the anodic Cl2 evolution process. Following up on previous work, Mishra et al. predicted maxima in i-E curves for chemisorbed states (E2I) . Also expressions for i-E curves have been derived for a two-electron reaction mechanism with an adsorbed intermediate (E22) .

Several worthwhile papers have appeared on the square- wave voltammetry of surface reactions. SWV was used to characterize quasi-reversible surface waves using the COOL nonlinear least-squares algorithm for data analysis. Various SWV peak shapes were observed, theoretically and experimentally for the azobenzene system, that were dependent on the rate constant, the S W amplitude, and the pulse width (E23) . O D e a et al. have also given SWV theory for a totally irreversible electrolysis of an adsorbed species. Experimental voltammograms were compared directly in real time with a numerical solution of the boundary value problem using the COOL algorithm to yield estimates of the transfer coefficient and the rate constant (E24) . An easily implemented theory for quasi-reversible cyclic SWV for a surface-confined redox couple was given by Reeves et al. (E25) . Their model assumed that lateral interactions among adsorbed species were negligible, that all surface sites were equivalent, and that there was no diffusional component of the current from solution species. Rate constants were extracted from the peak separations in the classical manner of cyclic voltammetry. Stripping SWV theory was developed for monomolecular layers of reversible, quasi-reversible, and irreversible M/Mn+ couples in a quite general fashion (E26) . In other articles, stripping voltammograms of simple ionic salts were analyzed in terms of theory that embraced two activity models for the interfacial species (E27); reversible and quasi-reversible stripping of insoluble Hg salts accumulated at Hg drop electrodes was treated (E28); semiintegral voltammetry was applied to situations where weak adsorption exists and both surface and diffusional waves are observed (E29); and surface coverages were measured using a combination of chrono-

coulometry and semiintegral voltammetry for situations where both surface and diffusion components contributed to the current (E30).

In a paper that illustrates well the difficulty of data interpretation, Kano and Uno have analyzed the quasi- reversible surface wave of several quinone couples in terms of two mechanisms: (i) a one-step, two-electron process; (b) a two-step EE process. In both cases Frumkin-type interactions between adsorbed molecules were taken into account and a Laviron approach was followed. They found somewhat better agreement with theory for the two-step EE mechanism (E31) . Simulation of reversible CVs where both Ox and R obey Frumkin-type adsorption isotherms using an orthogonal collocation method demonstrated the effects of interaction parameters (E32) . The general CV behavior was that of the classical Wopschall and Shain article. An earlier paper from the same group concerned the effect of coadsorption of an electroinactive product of a follow-up reaction (E33). Jin and co-workers have also presented theory for quasi-reversible surface waves in a manner similar to that of Laviron with slight modifications (E34-E36). Their treatments apply to various transformation voltammetries. Engelman and Evans simulated the chronocoulometric response for the situation of simultaneous adsorption and desorption of the product of an electrode reaction (E37). Input parameters for their program included rate constants for both the deposition/dissolution and the adsorption/desorption processes.

Chronopotentiometric theory was presented for the process, aA + n e- = bBads, assuming various electrode geometries and current/time excitation functions (E38).

Recent treatments of the metal dissolution problem include an analysis of the steady-state i-E curves for an EEmechanism, assuming Butler-Volmer kinetics and potential independent constants for irreversible desorption steps (E39), and a calculation of the current distribution in a corroding pit using conformal mapping techniques (E40).

Several papers havedealt with the effects of rough or fractal surfaces on double-layer impedance, mass transport, current density, etc. ( E 4 1 4 4 4 ) .

Mercury Electrodes. A study of the adsorption of iodide at the H g / l M NaClO interface between 30 and 453 K is notable for the wide temperature range studied (E45) . Partial charge transfer was invoked to explain the data. Isotherm parameters for the adsorption of iodide on Hg from ethanol were compared to values in eight other solvents (E46). Specific adsorption of halide ions at the Hg/CH&N interface was studied using classical techniques (E47) , and differential capacity measurements on the electrosorption of benzoic acid at the Hg/H20 interface indicated a “gas-to-solid” phase transformation that was driven by attractive dispersion forces (E48) .

Volume 349 of the Journal of Electroanalytical Chemistry, which consists of papers dedicated to Professor Lucien Gierst, contains several accounts of the formation of condensed films at mercury electrodes (E49-E53). Capacitive pits and condensed layer formation was described for thiouracil from CH3CN ( E M ) , methylisoquinoline (E55), and N B q + on Hg ( E M ) . The adsorption of 28 heterocycles and naphthalenes on Hg was analyzed in terms of an “intrinsic” Gibbs adsorption energy and a partial charge-transfer coefficient (E57).


Several research groups have focused their attention on reorientation phenomena. Adsorbates studied include methylpyridines (E58) , 4-phenylpyridine (E59) , uracil (E60), and nicotinic acid (E6I ) . The article of Werner et al. on the adsorption of aniline is noteworthy due to the simultaneous differential capacity and spectroelectrochemical measurements of the Hg interface using second harmonic generation techniques (E62) . At negative potentials, where the aniline molecules are oriented perpendicular to the electrode surface, the SHG signal was only dependent on the metal electrode.

Other studies include the report that the self-assembled monolayer of a C16 alkanethiol insulated Hg by a 1-V range (E63) and accounts of the adsorption of the zwitterion methionine (E64) and the highly symmetrical pentaerythritol molecule at the Hg/NaF(,,, interface (E65) . The adsorption of a 1,4-benzodiazepine on Hg was measured in a chronocoulometric study (E66) and CVs of benzo[c]cinnoline were interpreted by assuming Langmuir isotherms and diffusional mass transport of one of the redox partners from the bulk of the solution (E67).

Capacitance/time transients at the Hg/H20 interface have been analyzed in detail for the adsorption of Bu4N+ ions (E68) , 5-methyluracil (E69), and 2-thiouracil (E70) . In the Bu4N+ system, the pit nucleation and growth was independent of the nature of the anion at low concentrations, but became anion dependent at higher concentrations. Papadopoulos et al. used phase-sensitive ac voltammetry to construct c d l vs E curves for different times during the adsorption of sodium dodecyl sulfate at Hg (E71), and Tomaic et al. obtained the volume of surface-active condensates such as methyl oleate and squalene from analysis of current/time transients at the DME in seawater solution (E72) .

CVs of the Hg(cyclam)2+/Hg couple at Hg were complicated by base hydrolysis of the free ligand and the appearance of the Hg(OH)z/Hg wave (E73) . In a similar study, adsorption of Ni(cyclam)2+l+ was found at Hg where the Ni(I)ads complex was involved in the electrocatalysis of C02 reduction ( E 7 4 ) . Solvent effects on the kinetics of a (NH3)&o(III/II) coupleadsorbed on Hg via a bridging ligand were correlated with longitudinal relaxation times for Debye solvents ( E 7 5 ) .

A Fourier transform method was used to aid in the resolution of the diffusion peak and the postpeak that were seen in the differential pulse polarograms of the Pb2+/Pb- (Hg) system in chloride media where there is weak adsorption of reactant (E76) . Markedly different inhibitory behaviors were observed in the polarography of Cd2+ and Cr042- at n-hexyldecyltributylphosphonium-coated electrodes (E77) .

The anodic formation of HgS films was reported to proceed via successive deposition of 2-D monolayers and 3-D islands (E78) . Mattsson et al. studied the electrocrystallization and stripping of HgSe films which had been formed by the reduction of Se(1V) or by the oxidation of H2Se (E79) . In the presence of selenate, the anodic polarographic current was reported to be controlled by the precipitation of Hg2SeO4 (E80) .

In the miscellaneous class, Kruijt et al. used a light scattering method to study the diffusion-controlled growth of an assembly of Hg spheres on a Pt surface held at constant potential ( E 8 I ) .

Carbon Electrodes. Considerable progress has made in the last two years in understanding the fundamental surface electrochemistry of carbon electrodes. Notable among the contributions are those of McCreery and his students, who have continued their penetrating research using surface Raman spectroscopy, a variety of nonfaradaic electrochemical measurements, electron-transfer rates of the Fe(CN),j3-I4- and related couples, surface imaging methods, and other methods to characterize HOPG and glassy carbon (GC) electrodes. In addition, the advent of surface microscopies into various electrochemistry laboratories has provided remarkable atomic level insight into what is going on at the carbon/solution interface during electrolysis.

Kneten and McCreery reported that the electron-transfer (ET) rates of 13 redox couples were 1-5 orders of magnitude slower on basal plane HOPG than on laser-activated GC. Possible reasons advanced for the low rates on HOPG were the low density of electronic states in this material, the hydrophobicity of the surface, and the role of the GC surface in promoting H+ transfer-coupled multistep processes (E82) . The role of defect density on the basal plane of HOPG has been highlighted in several publications from McCreery's laboratory. For the anthraquinonedisulfonate system the values of ko, Cdl, and the surface coverage (I'T) were dependent on the defect density for HOPG (E83) . Highly irreversible CVs were seen for the Fe(CN)63-/4- couple on defect-free surfaces. Intercalation of HOPG in aqueous acid solutions was studied by in situ Raman spectroscopy (E84) . In 1 M H3P04, neither intercalation or lattice damage was observed at potentials up to 2.0 V vs SSCE, while in 1 M H2S04, HNO3, or HC104, intercalation always preceded or accompanied lattice damage.

Slow ET was seen at fractured GC or HOPG electrodes for the aqueous Fe3+I2+, Eu3+I2+, and V3+12+ couples, consistent with their low homogeneous self-exchange rates (E85) . However, even slight oxidation of the carbon surface gave large increases in the observed rates, suggesting oxide mediated inner-sphere catalysis via intermediate surface complexes.

SERS of GC and HOPG electrodes after deposition of 0.2 pmol/cm2 metallic silver permitted the formation of graphitic oxide to be distinguished (E86) . For unadorned surfaces, the electrochemically formed graphite oxide layers were indis- tinguishable in the SERS spectra. Electroreflectance spectra of methylene blue on HOPG gave evidence of three different adsorption states, two of which on the basal plane were separated by ca. 0.1 V (E87) .

Goss et al. reported the first in situ imaging of blister formation and collapse at HOPG electrodes under oxidative cycling in HNO3(,,, (E88) . They proposed a detailed mechanism for the submonolayer oxidation that involved electrolyticgas evolution at subsurface active sites. The blisters were 20-1000 nm in height and 0.5-50 pm at the base. Other in situ STM and AFM imaging of carbon electrodes included the study of Hendricks et al. on lead deposition on HOPG that was previously decorated with monolayer deep pits. Lead deposition and stripping at the rims of the pits can be seen in the published images (E89). Bard's group also achieved monolayer etching of the basal plane of HOPG using a STM tip under positive bias (E90). Lines and widths as small as

316U Analytical Chemistry, Vol. 66, No. 12, June 15, 1994

10 nm and squares 25 X 25 nm were formed. Others have used STM to follow the nucleation and 3-D growth of Pt deposition at HOPG surface defects (E91) , the formation of condensed layers of adenine (E92), and the deposition of oxometalates (E93) .

Glassy carbon surfaces have been most intensely studied, no doubt due to their favorable characteristics as working electrodes. An important account of the modification of glassy carbon electrodes (E94) also gives a very thorough review of GC as a solid electrode material.

The McCreery in situ laser activation technique for GC surfaces at power densities below 30 mW/cmz produced only slight changes in the SERS spectra, the l?T value for phenanthrenequinone, Cdl, and the SEM appearance of the polished surfaces (E95). However at fractured GC, or at fractured GC activated with three 70 mW/cmz laser pulses, a ko of 0.4 cm/s was measured for the Fe(CN)63-/k couple in 1 M KC1. STM images of GC surfaces that had been subjected to several pretreatment procedures showed varying degrees of roughness (E96). However, ET rates as measured by the ko for Fe(CN)63-Ik did not correlate with the surface roughness. This observation was said to be consistent with the previously widely held view that electrode activity is determined, to a large extent, as a result of active site exposure by means of whatever activation method is employed.

Transient currents, which had components on the millisecond time scale, were produced at GC electrodes by intense laser pulses (9 ns at 1064 nm). They were attributed to perturbation and restoration of the diffuse double layer and adsorbed ions (E97).

Zhang and Coury have made the useful observation that sonication of GC electrodes in dioxane leads to increased ET rates for aqueous redox couples (E98) . Electrodes treated in this manner are more prone to adsorb redox-active compounds than more conventionally treated electrodes and remain active in aqueous solutions for days. Firouzi et al. imaged GC surfaces using phase detection interferometric microscopy. In NaOH(,,), application of 1.5-2.0 V vs SCE for several seconds generated mesas with heights up to 250 nm and diameters on the order of 30-70 pm (E99). An in situ ellipsometric study of the electrochemical activation of GC indicated formation of a highly porous, hydrated surface layer, which increased monotonically with activation time (E100). GC electrodes activated in air at 400-800 OC or in steam at 790-980 OC gave CVs that exhibited a quinone/hydroquinone- like couple (EJOI) .

An extensive account has appeared concerning the modification of GC, both surface and homogeneous modification, by low-temperature thermolysis of poly(pheny1ene diacetylene) precursors (E94) . Homogeneous incorporation of Pt, for example, into GC produced solid electrodes with electrocatalytic response for the reduction of 0 2 and H+. These novel materials were prepared by thermolysis of either mixtures of platinum oxide microcrystallites in a carrier polymeric precursor to GC or an organometallic polymer containing covalent Pt(0). TEM of the electrodes indicated a narrow size distribution of Pt clusters in the doped GC, with an average diameter of ca. 1.6 nm (E102). Chlorine- and fluorine-doped GC was synthesized by this method using perhalogenated oligomeric materials ( E l 03 ) . Electrodes of these materials

exhibited reasonably fast kinetics for the Fe(CN)&" couple, and interestingly, the fluoro-GC had very low double-layer capacities, on the order of 8 pF/cmZ.

Several more conventional modifications of GC surfaces have been pursued in the past two years. Tateishi et al. found that ultrafine gold particles, 1-12 nm in diameter deposited on GC, produced an active surface for the oxidation of ethanol and acetaldehyde in alkaline solution ( ~ 0 4 ) . Similarly, silver- modified GC was an efficient substrate for the oxidation of small organics (E105), and GC electrodes modified with the NiO/NiOOH couple worked well for the amperometric detection of aliphatic alcohols (E106). Kulesza et al. reported that the use of a Pt counter electrode in acidic media can lead to electrodeposition of Pt particles with diameters of 20-40 nm on graphite cathodes (E107). The electrocatalytic oxidation of As(II1) was used as a sensitive indicator for the presence of the Pt particles. Several Russian groups have reported the modification of GC with fluorosulfonic groups (E108, E109) or with CF, groups (E110). Prewaves in the CVs of aromatic carbonyl compounds at GC electrodes were attributed to acidic surface functionalities interacting with the C=O group of the carbonyl compound (E111, E112).

GC electrode surfaces have been modified with covalently attached groups by the reduction of aromatic diazonium salts (E113, E l 14). For example, attachment of phenyl groups at coverages corresponding to a close-packed monolayer was demonstrated. The surfaces, which could be modified further by chemical reactions, were stable to ultrasonic cleaning and persistent over months.

Several interesting surface electrochemical investigations have been carried out on carbon fiber electrodes in conjunction with their use as UMEs. Pantano and Kuhr performed sophisticated imaging of 10-pm fiber UMEs by two methods: (i) fluorescence from fluorophores attached to surfacecarboxyl groups via a linker arm containing a biotin-avidin complex and (ii) luminol ECL generated at ET sites on the surface. Surface heterogeneity was evident at the submicrometer level in the polished and electrochemically treated surfaces (E1 15) . Kawagoe et al., who analyzed the pH dependence of both quinone reduction and dopamine oxidation at carbon fiber electrodes, concluded that there were mechanistic differences between the reactions on carbon fiber and on conventional electrodes (E116).

Several papers have described the effects of electrochemical pretreatments of carbon fiber electrodes (E1 17, E l 18). Swain and Kuwana found that Dupont pitch-based carbon fibers, which had been subjected to a sequence of high-current anodizations, underwent a surface-reforming process when followed by a vacuum heat treatment (E119). The ion- exchange properties of oxidized carbon fiber bundles have been exploited in two studies of Jannakondakis and co-workers (E120, E121). Theionexchangecapacityofthefiber bundles was estimated at ca. 1 mequiv/g. Carbon fiber UMEs with cation selectivity were prepared by electropolymerization of phenolic compounds bearing ion-exchanging carboxylic or sulfonic groups (E122). Anodic oxidation of pyrolytic graphite in alkaline solution did not destroy the surface structure while introducing hydroxyl groups (E1 23). In acid, oxidation occurred to depths as great as 40 nm from the edge surface.

Analflical Chemistry, Vol. 66, No. 12, June 15, 1994 377R

Several articles with innovative aspects have appeared describing carbon-based working electrodes. DNA-modified glassy carbon, immobilized via covalent bonds between deoxyguanosine residues and surface carboxylate groups, functioned as an electrochemical probe for the complementary oligonucleotide strand (E124). The electrochemical signal was that of C0(phen)3~+/~+ preconcentrated by the double- strand hybrid structure. McFadden et al. prepared carbon electrodes by pyrolysis of natural gas onto Macor, a machinable ceramic substrate (E125). ET rates on these surfaces for the Fe(CN)63-/4- couple were comparable to those obtained on conventionally polished GC. A highly active electrocatalytic porous carbon surface for 0 2 reduction was prepared by adsorbing anionic Co complexes into oxidized poly(pyrro1e) followed by heat treatment a t 820 "C under nitrogen (E126). A TEMPO-modified graphite felt electrode was used for the efficient electrocatalytic coupling of methylquinolines ( E l 27). Wang et al. (E128) evaluated epoxy-composite pellets as voltammetric working electrodes that were fabricated from carbon aerogel foams with high surface area and ultrafine pore sizes (C50 nm). Two groups have used boron-doped diamond films as working electrodes (E129, E130). The reduction of nitrate to ammonia in alkaline solution proceeded withgood Coulombicefficiencyat oneofthesesurfaces (E130). Screen-printed carbon electrodes have been promoted as amperometric sensor electrodes (E131, E132). Conducting salt/silicone oil paste electrodes (E133) and metal-dispersed carbon paste electrodes (E134) were found to be electrocatalytically active.

Studies on adsorbed molecules on graphite electrodes are cited here and in the vast section F below on modified electrodes. The properties of ruthenium(II1) oxide and cyanide films on carbon substrates for electrocatalytic oxygen atom transfer reactions has been examined. Mixed-valent Ru( II1,IV)-oxo centers were found to show specific reactivity toward As(II1) and CH30H oxidation (E135). Pyrolyzed Fe and Co tetraphenylporphyrins and Fe- and Co-crowned phthalocyanines were evaluated with respect to electrocatalysis of the 0 2 reduction (E136, E137); covalently attached Co'Itetraphenylporphyrin on glassy carbon effectively electrocatalyzed the reduction of C02 to CO (E1 38); an adsorbed Cu-phenanthroline complex on graphite electrocatalyzed the reduction of 0 2 and H202 via an EE mechanism (E139- E1 41); an adsorbed electroactive alizarin quinone, with the ability to complex Fe(III/II) couples, mediated the reduction of 0 2 and H202 at graphite electrodes (E142); and chloro- (phtha1ocyanine)rhodium complexes on HOPG underwent a slow solid-state electrodimerization that was coupled to the surface redox chemistry ( E 1 4 3 ) . Finally, in several studies Bond and co-workers have obtained meaningful voltammetry of water-insoluble compounds by mechanically transferring them to solid graphite electrode surfaces where surface redox reactions could be carried out in aqueous electrolyte solutions (E144 , E145) .

On the basis of the number of papers and their volume, surface electrochemists have been busy researching a variety of well-defined single crystal electrodes in the last two years. Interlaced with diligent effort at characterization of the interfacial structures and mechanistic phenomena are two major themes: documentation of the role

Single Crystal Surfaces.

of surface crystal structure on interfacial phenomena and the study of surface reconstruction reactions. It is now clear from numerous examples that surface structure can have remarkable effects on the mechanisms of a wide variety of electrode reactions. In many cases this has provided great detail on the nature of intermediates and key steps in these processes. In addition, in the past year or so there have appeared several really elegant applications of the new surface microscopies, e.g., STM and AFM, to the study of phenomena at single crystal interfaces.

Platinum(n,n,n). Examples of surface structure-sensitive reactions are the oxidation of small organic molecules such as glucose (E146), squaric acid (E147), and ethylene glycol (E148) at Pt single crystal electrodes in aqueous acid solution. In the work of Llorca et al. (E146), voltammetric currents were correlated with edge site processes. Different crystal faces of a working electrode will display widely different activities under identical conditions. For example, Pt( 1 10) was found to be most active for the oxidation of squaric acid (E147) and ethylene glycol (E148), while P t ( l l1 ) was the most active for the electrooxidation of glycerol in alkaline solution (E149) . For the oxidation of glucose, Tafel slopes of 120 and 60 mV were obtained on Pt( 11 1) and Pt(100), respectively, along with different adsorbed intermediates, gluconolactone on Pt( 11 1) and CO on Pt( 100) (E150). On the other hand, the oxidation of glyoxylic acid in H2S04(aq) was reported to be mostly insensitive to the structure of Pt single crystal electrodes (E151).

On the cathodic side, in situ electrochemical mass spectroscopy (EC-MS) clearly showed that only the Pt(100) face was active for the complete hydrogenation of benzene to C6H12 (E152) . Benzene was desorbed from the (111) face and partially desorbed from the (100) face. Another EC-MS study also revealed significant differences in the operative mechanisms for the oxidation of ethylene on Pt( 11 1 ) and Pt ( l l0 ) surfaces (E153).

Interestingly, oscillatory phenomena have been reported to be structure sensitive. Potential oscillations were seen during the oxidation of formic acid on Pt(100), but not on P t ( l l1 ) (E1 5 4 , and during the electrocatalytic oxidation of H2 in the presence of Cu(I1) and C1- at Pt( 11 1) and Pt( loo), but not at Pt( 110) (E155).

For inorganic systems, well-defined voltammograms for HN02/NO were obtained at Pt( 11 l ) , but not a t Pt( 100) or P t ( l l0 ) surfaces (E156). Rodes et al. (E157), however, reported irreversible oxidative adsorption of N O in a CV study of the reduction of nitrite at Pt( loo), and reduction of N02- and NO to NH3 proceeded with an efficiency of >80% at Pt( 100) surfaces (E158). For hydrazine oxidation in acid, stable irreversibly adsorbed species were found at Pt( 1 lo), while reversible adsorption, without charge transfer, occurred on Pt(100) and Pt ( l l1 ) (E159). Nishihara et al. found competitive adsorption with H+ on both terrace and step sites for the oxidation of hydrazine at Pt(332) and Pt ( l l1 ) in H2-

The adsorption of HS04- (E161, ,5162) and phosphate ions (E163) on Pt was sensitive to the surface geometries. The hydrogen region electrode process in NaOH(,,) was found to be strongly dependent on the exposed crystal planes at Pt low-index and stepped surfaces ( E l 6 4 ) . Adsorbed Pd atoms

SO4,aq) (EI60) .


on Pt( loo), -( 11 l), and -( 110) exhibited different hydrogen adsorption behavior (EZ65), and the growth of Pt oxide films wasfasteronPt(ll0) thanon-(loo),-(11 1)orpolycrystalline surfaces (EZ66).

Even the electropolymerization of 3-methylthiophene was dependent on the crystal structure of the Pt anode (EZ67). Likewise, the optical properties of Prussian-blue films, electrochemically grown on Pt( 11 1) and Au( 11 1) substrates, were similar to those on glassy carbon, while on Pt( 110) little film formation was seen (E168).

Surface reconstruction phenomena have been found to be structure sensitive as well. Rodes and Clavilier, for example, found that, for stepped-terrace Pt surfaces, the reconstruction phenomena, which could be rationalized in part by a hard- sphere model of the surface, were distinctly dependent on the width of the terraces (EZ69). Restructuring was indicated for Pt( 1 10) undergoing the hydrogen adsorption process in carbonate and bicarbonate solutions (E170) and for Pt( loo), -( 1 lo), and -( 11 1) surfaces in neutral phosphate buffers (E17Z). However, specific adsorption of anions on Pt( 100) in acid did not induce irreversible surface reconstruction (E172).

Sumino and Shibata have reported the surface transformations of electrodeposited films of Pt on polycrystalline substrates, which can have (100) or (110) orientation, depending on the experimental conditions (EZ73, E174). Clavilier and Rodes investigated the effect of the quenching temperature on the CV response of Pt (3 3 1 ) , - (5 5 3), and - (443) surfaces (EZ75).

Two major groups have addressed difficulties in the evaluation of absolute surface coverage of adsorbed CO on single crystal electrodes (E176, E177). Related to this is the difficulty of determining the Epzc for single crystal electrodes when reconstruction occurs (EZ78). Orts et al. reported that higher CO coverages were reached in solution than in the gas phase for Pt( 1 1 1) in H2S04(aq) (El 77). Oxidation of CO and CO adlayer formation continue to be popular subjects for study at single crystal electrodes (El 79-EZ81). Minimal toad, poisoning was reported for the oxidative dissociation of methanol at Pt(100) in Na2C03(,,) (E182) and for the oxidation of glycolic acid at Pt( 11 1) and Pt( 110) surfaces (E1 83).

Detailed mechanistic studies on the important methanol oxidation process included a study in CD30H and CH3OH at Pt single crystal surfaces which reached the conclusion that a C-H bond was broken in the initial step (EZ84). This is in contrast to the UHV decomposition where 0-H undergoes initial scission at Pt.

The orientations of nitrogen heterocycles such as substituted pyridines at P t ( l l 1 ) surfaces have been deduced by a combination of surface spectroscopies and electrochemistry (EZ85, EZ86). In several instances, surface layers, which were stable under vacuum, displayed the same electrochemical behavior before and after evacuation.

Gomez and Clavilier studied Pt(l10) with a view to the role of surface domains and their size on the hydrogen desorption process (E187). Mixed adlatticesofC0 and iodine produced immiscible domains on Pt( 1 11) surfaces (E188). Optical second harmonic generation methods applied to the

Pt( 11 1)-iodine surface revealed symmetry changes of the monolayer structure (EZ89).

The electrocatalytic role of bismuth adatoms has been addressed by several authors. Chang et al. attributed the 30-40-fold enhancement of formic acid oxidation rates at Pt(100) in HC104totheattenuationofCOad,coverage(EZ90). Formic acid oxidation was also catalyzed on Pt( 1 1 l) , although the major poison was not toads. In contrast, in the presence of predosed Bi, methanol oxidation was diminished on both Pt( 11 1) and -( 100). Campbell and Parsons also found that the oxidation of methanol was inhibited by submonolayer and monolayer coverages of both Sn and Bi on single crystal, polycrystalline, and dispersed Pt electrodes and that Bi submonolayers on Pt( 11 1) enhanced the oxidation of formic acid (E191). Weaver’s group has also studied the influence of Bi adatoms on the oxidation of ethylene glycol at Pt( 11 1) (EZ92). The redox behavior of Bi on Pt( 11 1) indicated that the adatom sites were dependent on the extent of surface coverage (E193).

Copper deposition onto Pt single crystal electrodes has been the topic of several detailed studies. Reports have noted the dramatic effect of adsorbates on the UPD of Cu on Pt(n,n,n) electrodes. Adsorbates studied include anions such as C1- and HS04- (EZ94, EZ95) and organic molecules such as hydroquinone (EZ96, E197). Cu, Pb and CO adsorbates on Pt( 11 1) in acid inhibited hydrogen adsorption and decreased the voltammetric peak presumably due to HSO4- adsorption (EZ 98). Cadmium submonolayers also effect the adsorption of HSO4- on Pt( 11 1) (E199). Along this line, Varga et al. reported that Cu deposition on Pt( 11 1) produced active and inactive adlayers toward bisulfate adsorption (E200). In one of the more detailed studies, Michaelis and Kolb correlated the voltammetric waves in HzS04(aq) with copper deposition initially into every other trough in the Pt( 1 lo)-( 1 X 1) surface, followed by complete monolayer coverage in every trough in the second process (E201). In situ STM of Cu UPD on Pt( l l1) had previously indicated a two-step process (E202). Leung et al. explained apparent discrepancies between stripping coulometric charge and theory for complete monolayer coverage of Cu on Pt( 1 11) surfaces by partial charge transfer to the substrate (E203, E204).

In the UPD of silver on iodine-covered Pt( 11 l ) , the Ag deposited underneath the iodine layer to form a Pt( 11 1)AgI surface (E205). At a thickness of two monolayers, the adsorption behavior of bisulfate on Ag deposited on Pt( 1 11) was similar to that on bulk silver (E206). Other studies include the concentration dependence of the UPD of Ag on Pt( 11 1) (E207), the epitaxial growth of Pd and Rh monolayers on Pt(l1 l)andPt(100) (E208),andtheadsorptionofGeadatoms on Pt single crystal electrodes (E209).

Gold(n,n,n). Reconstruction phenomena have been promi- nent in studies using gold single crystal electrodes. Several groups have investigated the anion-induced transformations of (5 X 20) to (1 X 1) structures for Au( 100) electrodes (E214 E21Z). In a STM study, Gao and Weaver found that, in the presence of iodide, the conversion of the square planar (1 X 1) surface to a hexagonal reconstructed phase was remarkably rapid (<0.2 s) for Au(100) in aqueous solution (E2Z2). In situ STM of Au( 1 1 1) revealed potential-dependent formation of a ( d 3 X d3)R3Oo adlattice structure in NaI and NaBr


solutions (E213,E214) and in HC104 (E215). STM images of flame-annealed Au( 100) surfaces clearly showed that cooling the surfaces in water prevented reconstruction of the surface (E216). However, E cycling to E C Epzc gave rise to ( 5 x 27) domains in the STM images; see also ref E217. Changes were also seen in the differential capacity consistent with these results.

The effect of organic adsorbates (usually stabilization) on the surface structure of gold single crystal electrodes has been reported (E218-E221). The adsorption of pyridine on Au(100) was shown to be complicated by the surface reconstruction into a hexagonal( 1 1 1)-like surface at negative potential (E222). On the unreconstructed surface there was no phase transformation from flat to vertical orientation of the adsorbate.

STM images of Au( 11 1) in dilute CN- solution revealed the presence of monolayer pits on terrace locations that collapsed in minutes presumably via a mobile step edge/ adatom diffusion mechanism (E223, E224). Nichols et al. also obtained STM images of Cu deposition on Au( 11 1) and -( 100) surfaces which showed crystallites at the step edges (E225). For Au( loo), initial Cu deposition was at the rims of gold mesas that were one atomic layer high and 5-30 nm in diameter (E226). In the presence of crystal violet, the crystallites were flatter and spread more uniformly over the surface as the deposition proceeded. Gao and Weaver reported potential-dependent adlayer transformations for STM images of Au( 11 1) in the presence of the I-/I3- couple (E227) . At the onset of iodide oxidation, linear polyiodide strands were evident in the images.

Pettinger et al. have followed the surface reconstruction of Au( 1 1 1) using SHG spectroeIectrochemical techniques (E228, E229). The SHG response from Au( 11 1) also gave details on the adsorbate/surface interactions during the UPD of Cu, Ag, Pb, and T1 (E230) .

Metal deposition on gold single crystals continued to be a popular topic. Ullmann et al. achieved the deposition of very small Cu(0) clusters, typically three to five atoms, on Au( 1 11) by potential control of the STM tip in a CuSO4/ HzS04 solution (E231) . Pb clusters were observed to grow along a reconstruction edge on Au( l l1) (E232) , and Hg overlayers on Au( 11 1) have been imaged by AFM (E233) .

Interesting papers on Ag UPD include an in situ surface EXAFS study at Au( 11 1) that found the Ag-0 internuclear distance to be invariant over a 0.8-V potential range (E234) . STM and AFM have also been performed on the Au( l l1) Ag/UPD interface (E235, E236). In the latter study, different images were seen in different aqueous electrolytes, indicating that the anion played an important role in determining the structure of the first monolayer. Lead UPD (E237) and Bi UPD (E238, ,5239) images were also obtained with AFM and STM techniques. In the former, lead island formation was seen and correlated with voltammetric peaks and electrocatalytic activity.

An “electrochemical atomic layer epitaxy” protocol was devised based on the successive UPD of atomic layers of As, by oxidative UPD of AsH3 solution, and of Ga by reductive UPD from Ga(II1) solutions. LEED was used to characterize the ordered stoichiometric coverages of Ga and As on Au( loo), -( 1 IO) , and -( 11 1 ) surfaces (E240, E241). Golan

et al. electrodeposited CdSe nanocrystals, “quantum dots”, in epitaxy with Au( 11 1) (E242). The spatial distribution of the crystals could be controlled by variation of the temperature and the ratio of the deposition time to the current density.

Adsorption of organic molecules at gold single crystal electrodes has been reported for p-toluenesulfonate on Au(3 11) (E243) , benzonitrile on Au( l l1) (E244), pyridine on Au(311) (E245) , and pyridine on Au(210), where comparison was made to pyridine adsorption at the (31 l ) , (1 lo), (loo), and (1 11) planes (E246). STM, AFM, and CV were used to study the DNA bases adenine, thymine, guanine, and cytosine adsorbed onto Au( 1 1 1) (E247). The Langmuir- Blodgett transfer procedure, i.e., the film pressure, was found to be sensitive to the surface structure for Au(l1 l ) , -(loo), and -(110) surfaces (E248).

LEED spectra, STM images, and differential capacity vs E curves have been acquired for the three vicinal orientations of Au( 11 1) singlecrystal surfaces (E249). Xing et al. observed that the two-electron oxidation of ascorbic acid was mostly insensitive to the surface structure for Au(l1 l ) , -(1 lo), and -( 100) electrodes (E250).

Other Metals. Data obtained at a Ag( 11 1) electrode were used to test the validity of the Gouy-Chapman theory (E251) . In a separate study, the effect of crystalline heterogeneity on the double-layer capacity was documented (E252). Anion adsorption on Ag( 11 1) was studied by impedance techniques (E253) , and the double-layer capacity of Ag( 100) in KPFqaq) was measured between 1.5 and 47 “ C (E254). In a compara- tive study of SCN- adsorption on Ag( 11 1) and Pt( 11 1) from Hubbard’s laboratory, protonation effects were detected in the high-resolution energy loss spectra of the interfaces (E255).

Nucleation rates of Pb on Ag(l11) were explained by a model that took into account substrate-induced strain in the UPD monolayer (E256). The ease of formation of T1-iodide layers was found to be the order Ag(l11) > Ag( 100) > Ag( 1 10) > chemically polished Ag > mechanically polished polycrystalline Ag in KI solution (E257). STM of Pb UPD on Ag( 100) and Ag( 1 1 1) electrodes revealed formation of well-ordered monolayers (E258).

Electrochemical reordering of a disordered palladium oxide surface was demonstrated by McBride et al. (E259) . They found that treatment of a disordered oxidized surface with dilute NaI solution at a potential where oxide was reduced resulted in the appearance of the LEED pattern of a Pd( 100) surface. The same laboratory reported reorganization of surface bonding structures upon oxidation of CO adsorbed on Pd( 1 11) (E260) and the dissolution of Pd in a layer-by-layer process without loss of an iodine monolayer on a Pd(ll1)- iodine surface (E261) . Two-stage adlattice formation was suggested for the UPD deposition of Cu on Pd( 100) (E262), and thin Pd overlayers electrodeposited on Au( 11 1) and Au( 100) electrodes were shown to behave in a manner similar to Pd( 11 1 ) and Pd( loo), respectively (E263) .

Differences were found in the measurement of CO surface coverage values on Rh( 100) electrodes by coulometric and FT-IR spectroscopic techniques (E264). Adsorption of bisulfate on Rh( 11 1) featured adsorption plateaus over a wide potential range, in contrast to the behavior at polycrystalline Rh electrodes (E265). Perchlorate anions were reported to decompose on polycrystalline Rh and Ir( 1 1 1) electrodes to


produce a surface species, probably adsorbed chloride, that inhibited hydrogen adsorption (E266).

Only negligible electrocatalysis was seen for the oxidation of methane when surface oxides and/or silver were deposited on Ru(001) electrodes (E267). Wang et al. have described a neat procedure for the preparation of Ni( 1 1 1) surfaces for electrochemical study. The surfaces, which were formed under UHV conditions, were protected with a layer of adsorbed CO prior to transfer to solution and electrochemical stripping of the CO (E268). The UPD of T1 and Pb on Cu( 11 1) films evaporated on mica surfaces was reported (E269), and an AFM study of potential-controlled oxygen adsorption on Cu(100) has appeared (E270). STM images were obtained of the silicon( 11 1) hydride phase that was revealed when an oxide layer was removed under potential control in HFg,) solution (E271).

Surface Imaging Techniques. As is evident in the previous section, surface electrochemists have been applying the various surface microscopies to the study of electrode interfaces since the initial introduction of these techniques. The student wishing a more complete compilation of references on this topic should scan citations from the above sections on UMEs and single crystal electrodes. The articles mentioned here are perhaps more technique oriented, although the distinctions are often arbitrary.

Vogel et al. published beautiful STM images of Pt single crystal electrodes subjected to the “iodine procedure” both in air and in electrolyte solutions (E272). The images, which were in accord with previous LEED ex situ results, were obtained using a noncommercial STM apparatus, details of which were given. A prospectus for STM/electrochemistry has been published that contains many examples and impressive STM images (E273). Schmickler and Widrig presented some theoretical considerations of the STM/Echem experiment (E274). The Poisson-Boltzmann equation was solved for a sphere-plane configuration as a model for the tipsubstrate geometry (E275).

Techniques for STM tip sharpening and related applications were extensively reviewed (E276). A combination of normal sharpening procedure under ac voltage with the tip oriented downward, followed by further sharpening with the tip oriented upward, was found to be effective for tungsten tips. Oxide layers on tungsten tips are easily removed in concentrated H F (E277). Details were given for the preparation of STM tips with reduced capacitive currents for use in a differential conductance mode of operation (E278) and for electrocoating STM tips with polyacrylic carboxylic acid (E279).

Surface microscopes have been used in novel ways to characterize and/or to spatially modify film electrode interfaces. For example, Murray’s group has reported a procedure to produce spatially patterned, laterally heterogeneous polymer- modified electrodes using in situ AFM (E280). They used an AFM tip to “nanodose” a defect in a thin film of insulating poly(pheny1ene oxide) (PEO). The defects were then filled by electropolymerized conducting polymers. Yang et al. proposed a STM technique to measure the thickness of polymer films on conducting substrates. The plot of tip current vs tip displacement exhibited linear regions due to (i) approach to the surface, (ii) penetration through the film, and (iii) contact with the substrate (E281). In situ AFM was successfully

used to follow the electrochemical formation of PEO (E282), while STM images of poly(N-methylpyrrole) were noisy, probably because the STM tip typically was buried in the poorly conducting polymer film (E283).

Sugimoto et al. used the Bard SECM technique in a direct- scanning mode to obtain images of a Prussian blue film electrode that showed cracks and grain boundaries at the submicrometer level (E284). Engstrom et al. employed SECM to map the local electron-transfer kinetics of reactions occurring at kinetically heterogeneous Pt disks or epoxy impregnated RVC electrodes (E285). Several other applications of the SECM technique have been cited above in the sectionon UMEs. The improvement in the technique involving small-amplitude modulation of the tip position seems especially important (B75, E286). This permits automaticdetermination of whether a surface is insulating or conducting.

Among the many applications of STM to electrochemistry are several reports of STM images of dissolving electrodes (E287, E288), of metal particles deposited in the pores of anodic aluminum oxide films (E289), and of electrochemically grown organic semiconductors (E290). In situ STM/Echem of silver electrodes revealed time-dependent smoothing of the surface during redox cycles (E291), and the fractal dimen- sionality of Au and Pt electrodeposits was determined (E292). STM images of DNA molecules have been obtained on Au(l l1) surfaces under potential control (E293). This particular application, and related methodology (E294), promises to become popular in molecular biology fields.

Fluorescence imaging of electrode surfaces was achieved by generation of OH- in weakly buffered solutions of fluorescein. Thus, reduction of H2O or 02, the latter at cathodic corrosion sites, converted the dye into a strong fluorescing species and produced images of the electrode surface (E295). Miller et al. imaged L-B monolayer films of a Ru-bpy surfactant by observing ECL with a sensitive CCD camera (E296). Finally, local ac impedances were obtained by measuring the potential difference between two microelectrodes in a probe assembly (E297).

Polycrystalline Electrodes. An interesting comparison of chronocoulometry, radiochemistry, and Raman spectroscopy applied to the measurement of pyridine adsorption on gold electrodes has appeared (E298). Agreement was found between surface concentrations determined by the first two techniques, but chronocoulometry, where double-layer, not faradaic, charge densities were measured, gave the better precision. Adsorption of HS04-, C1-, and I- on Pt was measured by three in situ methods: radiotracers, FT-IR, and ellipsometry (E299). Bell-shaped adsorption isotherms were reported for 20 organic compounds on Pt (E300), and the Epzc values and capacitance minima for Au were measured in NaF(,,) using a piezoelectric technique (E301). An extensive set of double-layer data at various metal electrodes in DMSO, DMF, PC, AN, MeOH, and H20 was collected and used to analyze metal/solvent interactions and the interfacial solvent structure (E302) .

Among the papers on the oxidation of methanol at solid electrodes are a study at mixed oxides of Pt and Sn (E303), a study of the effect of Ru deposition where RuOHad, intermediates were proposed (E304), a study of the effect of adsorbed Sn atoms (E305), a detailed examination of the


process at Pt-Ru alloys (E306) , and a report of the use of hydrophobic nickel electrodes coated with fine particles of tetrafluoroethylene (E307) . In situ FT-IR spectra revealed several intermediates in the process at Pt, including three forms of adsorbed CO, a COH species, and a CH-containing species (E308) . Surface-enhanced Raman spectra also have been obtained for this system (E309).

The surface electrochemical behavior of three isomeric pyridyl hydroquinones at polycrystalline Pt (and at P t ( l l1 ) ) was dependent on the orientation of the adsorbed monolayers (E310). Oxidation of ethylene glycol gave different product distributions on Au, Pt, and Ni electrodes (E311) . FT-IR spectra indicate C2 solution intermediates in route to oxalate and carbonate ions on gold electrodes, while formate was formed to the greatest extent on Ni. The electrocatalytic oxidation of toluene was seen at coatings of deposited hydrated platinum oxides on Pt, Ni, Ti, Fe, and glassy carbon supports (E312). Two pathways were described for the oxidation of phenol at Pt: one occurring at the inner Helmholtz plane, where ring cleavage took place, and one occurring at the outer layer, where a mixture of products was formed (E313) . Squaric acid oxidation on Pt gave extensive formation of toads and COz products over a wide potential range (E314) . Oxidation of surface mercaptoethanol films at Au proceeded by multiple pathways (E315).

Evidence was presented to indicate that the first monolayer of adsorbed thionine is electroinactive at Pt. On sulfur- modified Pt, however, the first layer of adsorbed material is electroactive (E316). In similar fashion, sulfur adlayers on Pt changed the irreversible phenothiazine oxidation into reversible CV behavior (E31 7 ) .

RDE and QCM measurement gave new insights on the well-studied iodine/iodide system at Pt in H2S0qaq) (E318) . Michelhaugh et al. found that even submonolayer coverages of adsorbed iodine gave fast kinetics for the quinone/ hydroquinone couple, which they took to indicated selective ET at iodine surface sites (E319) . Anodic 0-atom transfer electrode reactions were proposed for the oxidation of I- to IO3- at Pt, Au, Pd, Ir, and glassy carbon (B117), for anodic reactions at PbOz electrode doped with acetate (E320) , for the oxidation of oxysulfur anions at PbO2 (E321) , and for the determination of As(II1) at Pt where a key role was assigned to PtOH (E322) . Anodic Cl2 evolution at Pt was reported to take place on an oxide-free surface in anhydrous trifluoroacetic acid (E323) .

Oscillating phenomena continue to stimulate electrochemists, who have usually fingered CO,d, as a key intermediate in their mechanistic speculations (E3244E327). Wolf et ai. modeled the oscillating electrochemical reduction of peroxo- disulfate by a system of nonlinear differential equations based on a Nernst diffusion layer treatment for a diffusion current term and a Butler-Volmer expression with a Frumkin correction for the charge-transfer term (E328). Good agreement between theory and experiment was obtained. The potential oscillations seen in the galvanostatic oxidation of formic acid on Pt were directly coupled to frequency oscillations in the EQCM experiment (E329) . Finally, a true ac battery was based on an ingenious concentration cell that consisted of two mass-coupled oscillating half-cells. Typical specifica-

tions were period, 58 s; current, f 2 . 5 PA; and emf, f50 mV (E330).

The formation and growth of metal oxide films have been studied by a variety of methods including voltammetry, ac impedance, and EQCM. These include investigations of Pt electrodes (E331-E336), gold electrodes (E337-E340), and Pd electrodes (E341, E336). EQCM data indicated that the gold dissolution rate upon E cycling in H2S04(aq) was 550 ng/h (E337).

In the miscellaneous category, the relationship of area to volume of dendritic Ag deposits on polycrystalline Pt was found to exhibit fractal behavior with area = k ( ~ o l ) ~ / ~ , where D = 2.50 f 0.03 (E342). This value is consistent with a self-similar fractal surface. Finally, a description of a guillotine electrode, which was tested on A1 electrodes in aqueous solution, was noted (E343) .

Miscellaneous Electrodes. Several reports have appeared that featured superconducting working electrodes. Plots of cdl vs T for two T1-based high-T, superconductors immersed in fluid electrolyte solutions displayed abrupt changes in the region of Tc (E344) . An increase in faradaic current was observed for high- Tc superconducting electrodes in contact with Ag+ ion conductors at low temperatures (E345) . A role was suggested for Cooper pairs crossing the double layer and participating in the electrode reaction. A quasi-reversible, almost irreversible, CV for the ferrocene+/O couple was obtained at a Bi-Pb-2223 superconducting UME at 102 K (E346). Kuznetsov developed theory explaining the increase in current in the Tc region for superconducting electrodes (E347).

Conditions were given for the anodic electrosynthesis of millimeter-sized crystals of Bao.sKo.4BiO3 with Tc values of 30.5 K (E348). Superconducting thin films of Y-Ba-Cu-0 and T1-Ba-Ca-Cu-0 were electrodeposited at negative potentials in DMSO solution (E349) . Electrochemical Li- doping of high- Tc superconducting films resulted in an increase in a lattice constant and/or the T, value (E350). Electro- polymerization of aniline on the surface of YBa2Cu3O,-a produced a film with protective properties (E351). More interestingly, redox cycling of poly(pyrro1e) coated on thin superconducting films reversibly changed the Tc value by almost 15 K (E352) . The Cu(III/II/I) system was examined at the latter surface (E353), and Ma et al. successfully electrodeposited Cu contacts onto a superconducting substrate (E354) .

Several interesting working electrode materials containing titanium have been studied in the last two years. Titanium diboride, an electroconductive ceramic, exhibited a wide potential window and was used for the reduction of C02 (E355) . Ebonex, a conducting ceramic mainly composed of the Magneli phase of titanium oxides Ti407 and TiS09, coated with PbO2, was found to be a suitable anode for ozone generation (E356). A previous report from Pletcher’s group had described conducting titanium oxide ceramic electrodes (E357) . Polycrystalline thin films of cubic BaTi03 were prepared on Ti metal substrates by several methods, including an electrochemical anodization in Ba(OH)2 solution (E358).


F. MODIFIED ELECTRODES Charge Transport in Polymer Films. Several important

papers on this topic have appeared in the last two years. Attention is also called to the review of Inzelt, who has surveyed theory and experiment up to ca. 1992 (A40). Fritsch-Faules and Faulkner simulated lateral charge transport in a thin film of redox centers electrostatically held in a polymer matrix ( F I ) . Their model allowed for partitioning between the film and solution, which opened two diffusional paths for the ions in the charge transport process. In a nice experimental study, they determined the concentration profiles in methyl- quaternized poly(viny1pyridine) (PVP) films containing the Fe(CN)&/”couple by means of potentiometric measurement at arrays of 4-pm-wide Au electrodes in contact with the film (F2) . The concentration profiles under steady-state current flow between flanking electrodes were linear. The calibration curve relating potential to concentration was established by chronocoulometry in a companion paper (F3) . The behavior was found to be Nernstian in spite of (i) different extent of partitioning of ferri- and ferrocyanide, (ii) oxidation-state- dependent mass transport, and (iii) nonideal CV behavior. The charge transport was dominated by diffusion of the redox species through solution since the diffusion coefficients were 2-3 orders of magnitude greater in solution than in the film. The experiments of Larsson et al. (F4) on PVP films containing Fe(III/II) redox sites either directly bound to pyridine groups on the polymer or electrostatically bound to quaternary pyridinium sites relate to this model. In the former situation, the apparent charge-transfer diffusion constants (DcT) were almost 100 times smaller than in the more typical ion-exchange polymer.

The dynamics of electron hopping in assemblies of redox centers has been treated in a major contribution that is pertinent to charge transport in fixed-site redox polymers (F5). The authors found that when physical motion of the redox centers was either nonexistent or much slower than electron hopping, charge propagation was fundamentally a percolation process, in which electron hops occur between a random distribution of redox center clusters. In another paper, Blauch and Saveant modeled the charge transport by random walk of electrons through redox molecules in square and cubic lattices (F6) . Below a critical concentration, finite cluster size makes charge transport impossible. Further, in their treatment, the mean-field physical diffusion model of Dahms and Ruff was shown to be inapplicable to systems in which the contribution of physical diffusion to charge transport is small compared to that of electron hopping. Rapid bounded diffusion in systems where the redox centers are irreversibly attached to the supramolecular structure, on the other hand, gives rise to mean-field behavior when it exceeds the rate of electron hopping.

In another approach, Mohan and Sangaranarayanan incorporated an exponential dependence of electron hopping rates on distance into a generalized diffusion/migration equation for redox film charge transport (F7). Also Deiss et al. published a quitegeneral digital simulation of redox polymer CVs (F8) . Their calculation accounted for mass transport by diffusion and migration, electron hopping by a Saveant mechanism, homogeneous reactions in the film, heterogeneous reactions and C,-J at the membrane/electrode interface, and

Donnan partitioning at the membrane/diffusion layer interface.

Impedance techniques have been refined for the analysis of charge transport in polymer film electrodes and successfully applied, notably by Pickup and Albery and their respective co-workers. Ren and Pickup have published several studies where they used a transmission line equivalent circuit to analyze charge transport in ion exchange polymers based on poly(pyrro1e) (PPy) (F9-FI 1). They employed a porous electrode model and generally found that ion mobility limited the charge transport. A good example is their study of polymer films of 3-methylpyrrole-4-carboxylic acid, where ion mobility was lo3 faster than electronic conductivity (F9) . The results were interpreted using a two-phase model in which ion transport was due to counterions in the polymer phase and excess electrolyte in the pores. Fletcher also used a porous electrode model to interpret impedance data for conducting polymer electrodes (F12, F13). In a similar fashion the transmission line model of Albery and Mount was based on a porous electrode with organic polymer and aqueous pore phases (F14) . Resistances were obtained due to bimolecular electron exchange and anion buildup in the film. In another treatment of polymer film ac impedance, they proposed a transmission line model in which there were separate resistive rails for the cation and for the anion (F15). This would apply to the common situation when electron motion along the polymer backbone is faster than ion conduction in the pores.

Mathias and Haas have developed theory for ac impedance of redox polymer films under conditions where either electron hopping or ion migration is slow relative to the other (F16) . They assumed Donnan exclusion permitting only one mobile ion in the film. These authors have studied PVP films containing Os(bpy)z centers under conditions of four bathing electrolytes where the charge transport was via electron and anion motion only (F17) . (This paper gives a nice summary of the procedures for extracting parameters from raw impedance data.) In contrast to the above situations, ion transport in these films was found to be much faster than electron hopping, even for large anions such as toluenesulfonate.

The impedance response of poly(pyrro1e) bilayers, with perchlorate and poly(styrenesu1fonate) counterions, indicated that the redox reaction was outside-inside, i.e., began at the polymer/solution interface (F18) . This was consistent with a porous electrode model and with the redox polymer model of Albery et al. (F19) . On the other hand, a chronopotentiometric study concluded that an inside+mtside mechanism was operative for lightly doped PPy (F20).

Sharp et al. gave a clear account of the interpretation of impedance data for Nafion film electrodes containing O~(bpy)3~+/*+ and substituted ferrocene couples (F21). The dependence of the redox conductivity on the overall oxidation state of the film, in their view, was in agreement with an ion-pairing model in which electron hopping took place between, for example, a neutral Os(I1) site and a positive Os(III)+ site. Forster and Vos have reported correlations between DCT and the heterogeneous electron-exchange rate- ( k o ) for two redox polymers containing Os(III/II)-bpy sites (F22, F23). The effect of the extent of loading of O~(bpy)3~+/*+ in Nafion was significant when the amount of

Analytical Chemistry, Vol, 66, No. 12, June 15, 1994 383R

Os was greater than one-third of the available anionic groups necessary for charge neutrality in the oxidized state. In this case, the CVs exhibited two waves: a reversible surface wave for the Os(III/II) couple and an irreversible wave at greater potentials that involved ejection of the complex from the film (F24). The ejection was elegantly verified by SECM using a UME probe positioned above the film.

Mao and Pickup used RDE voltammetry of ferrocene to measure the potential profile across a substituted poly(pyrro1e) film. The gradient was nonlinear, which they took to indicate nonmetallic conductivity where the charge transport process is driven by a concentration gradient of oxidized sites in the polymer matrix (F25) .

Aoki and Heller measured apparent electron diffusion coefficients in a cross-linked redox polymer that contained Os(bpy)2 redox sites. In their interpretation of the data, they invoked hydration effects that were induced by counterions, ionic strength changes, or protonation of basic groups on the polymer backbone (F26) . Water transport was noted in EQCM studiesof PVPfilms containing Os(III/II)-bpy centers (F27) and poly(viny1ferrocene) films (F28, F29). Slow structural changes for related polymer films were seen when the electrodes were transferred between perchloric and toluenesulfonic acid solutions (F30) . For poly( l-hydroxy- phenazine) films, the typical featureless CV was shown to involve two ion-exchange coupled steps: one with proton transport and the other with anion uptake and solvent loss (F31) . Hydration effects were also noted for the solid-state charge transport in hexacyanoferrate films with fixed Fe(III/II) sites (F32) .

An equivalent circuit proposed for the interpretation of impedance data at redox polymer electrodes contained two capacity terms: one for the substrate/polymer interface and one for the polymer/solution interface (F33). Also the effect of surface roughness of the substrate on the impedance of polymer films has been considered (F34) . The combination of ac impedance spectroscopy and "electromodulated optical transmittance spectroscopic impedance" was used by Amemiya et al. to study charge transport in polymer film electrodes (F35, F36).

Hillman and Bruckenstein have pointed out the important role of slow solvent transport in several studies of the redox kinetics of permselective polymer films. Electron transfer, solvent uptake, and polymer reconfiguration in a cube scheme were incorporated into a general model (F37). Often observed phenomena such as "break-in" processes, charge and mass trapping, structural changes with redox cycling, and variation of charge transport rate and Eo' values with time were encompassed by their theory. For a polythionine redox film, the kinetics were described in terms of a scheme of squares involving electron, proton, and solvent transfer (F38) . The EQCM data showed that the coupled motion of electrons and protons preceded the rate-limiting solvent transfer in both anodic and cathodic steps. One of the later papers in the general Bruckenstein and Hillman treatment of the EQCM experiment has appeared in the last two years (F39). Proton transfer was also shown to be involved in the charge transport process operative in thin ubiquinone-Qlo films (F40) .

A two-phase model was employed to explain the surprisingly large electrochemical diffusion coefficients in polyacrylate

gels ( F 4 1 ) . In spite of high gel viscosities, high diffusivity in thecontinuous aqueous phase was invoked to explain the data.

Electrocatalysis at Modified Electrodes. This subject, a raison d'stre of modified electrode research, has seen relatively little theoretical activity in the last two years. The general treatment of electrocatalysis at polymer-modified electrodes containing microparticles stands out however (F42) . Equa- tions were derived for the flux as a function of the number of particles per unit volume, the film thickness, the substrate and mediator concentrations, and the particle radii. Eight cases were described, along with the respective flux equations, that differed in the reaction orders with respect to the above experimental variables. In a second paper on metal oxide/ Nafion composite amperometric sensors, the kinetics were cast in the context of the Michaelis-Menten formalism (F43) .

Anson and Xie have addressed several important aspects of data analysis for the estimation of rates of cross-reactions that occur during electrochemical catalysis at polymer- modified electrodes using the Koutecky-Levich equation (F44, F45) . In a later paper, a modified kinetic model, which assumed an array of film mediator couples with a Gaussian distribution of Eo' values, was developed (F46). When the parameters of the distribution were selected to fit the i-E curve for the non-Nernstian surface wave of the mediator couple, significant improvement in the agreement between experimental and calculated currents was obtained for several cases involving redox couples in Nafion coatings.

Numerous articles continue to be published on various polymer-modified electrodes designed to be catalytic for specific processes. The ones cited here will be organized in terms of the electrode reaction catalyzed and not by the nature of the polymer matrix. Electrocatalysis of 0 2 reduction was achieved at a porphyrin ligand coordinated by four Ru(NH3)5 groups in Nafion (F47), and by metal phthalocyanines in various matrices (F48-F50). Cobalt(I1) complexes in Nafion ( F 5 1 ) and Prussian Blue/poly(aniline) (F52) films catalyzed the reduction of C02. Electrocatalytic reduction of nitrite took place at quite positive potentials at PVP films containing Os-bpy complexes (F53, F54); a mixture of N20, N2, NH2- OH, and NH3 was obtained at thin polymeric films of an iron(II1) protoporphyrin (F55). Oxyanions such as chlorate and bromate were reduced at conducting polymer electrodes doped with molybdate species (F56, F57). Poly(pyrro1e) films were robust enough to mediate the reduction of dichromate in acid (F58). Electrocatalytic films for the reduction of the disulfide bond in cystine (F59) and for the Cu(II/I)-mediated reduction of cytochrome c and tyrosinase (F60) have been described. Substituted poly(pyrro1e) films with Pd(I1) and Rh(II1)-bpy centers were used, respectively, for the hydrogenation of organic compounds (F61) and the catalysis of hydrogen evolution (F62). Catalytic activity was imparted to insoluble liquid crystal films of a cationic surfactant on graphite electrodes by vitamin B I Z hexacarboxylate (F63).

On the oxidation side, several different polymer film electrodes have been used for the electrocatalytic oxidation of NADH (F64-F66). Pyrrole-substituted Mn tetraphen- ylporphryrins were precursors to catalytic polymer films for the epoxidation of alkenes and the oxidation of thioacetamide (F67). Ru(V/IV)-oxygen complexes in Nafion and poly- (pyrrole) films mediated the oxidation of alcohols (F68, F69).

304R Analytical Chemistty, Vol. 66, No. 12, June 15, 1994

Electropolymerization of several free-base and metalated porphyrins produced conductive redox polymers with electrocatalytic activity for a variety of reactions (F70, F71), and a porous Ti02 ceramic coated with Nafion containing RuOz/ IrOz catalyst was an efficient electrode for oxygen evolution (F72).

Polymer film matrices have been employed in enzyme electrodes since the initial work on things such as the urease electrode of Updike and Hicks. The use of redox polymers and conducting polymers in conjunction with mediating species continues to be an active research area. Many different variations, and some not so different, have been published in the last two years on this topic, especially with glucose oxidase as the enzyme system. Only a few of these will be mentioned here. Ye et al. described a glucose electrode, which was made with Heller’s epoxy redox polymer and a quinoprotein glucose dehydrogenase, that exhibited exceptionally high current densities, 1.8 mA/cm2 (F73). An improved glucose sensor was fabricated via the substituted pyrrole route using glucose oxidase that had been covalently modified with pyrrole (F74). Your reviewer also liked the description of a glucose sensor “switch” that was based on a poly( 1,2-diaminobenzene) film containing the enzyme, which was polymerized on top of a poly(ani1ine) electrode (F75). Another crafty approach was that of Anzai et al. who electrodeposited avidin on Pt and then complexed the surface with biotinylated glucose oxidase (F76).

The mediated redox enzyme concept has been applied to enzyme systems other than glucose oxidase to develop sensors for other species including amino acids (F77), fructose (F78), lactate (F79), NADH (F80), and others (F81).

Papers also continue to appear on electrocatalytic applications of surface-modified electrodes without a (often resistive) polymer film component. Some of these have been cited under Carbon Electrodes. Shi and Anson have studied their cobalt porphyrin substituted with Ru(NH& groups via pyridyl ligands when it is adsorbed on graphite (F82). The currents for oxygen reduction were greater at these surfaces than at Nafion film surfaces containing the same complexes, but the stability was not as good. In another study it was found that the number of Ru(NH& groups on the complex determined whether a two-electron or a four-electron pathway was followed (F83), with the trisubstituted pomplex giving the latter behavior. For protoporphyrin IX-modified glassy carbon electrodes a two-step reduction of 0 2 was observed for pH >12, and a four-electron reduction for pH <11 (F84) . Electrocatalytic reduction of 0 2 and H202 was also observed at pyrolytic graphite coated with Fe and Co phthalocyanines possessing fused crown ether substituents (F85) . The iron system gave a four-electron reduction wave for oxygen. Ni- tetraazamacrocycle surfaces were found to be electrocatalytically active for the reduction of C02 (F86) and for the oxidation of alcohols (F87).

Indium tin oxide (ITO) electrodes treated with Cl$3Co- (CO)4 produced SiCo sites that were reactive toward alcohol, amine, thiol, amide, and carboxylate functionalities (F88). This was the basis of a general method for modifying I T 0 electrodes.

Ion-Exchange Polymer Film Electrodes. Several thorough studies of Nafion membranes have appeared. Verbrugge et al. measured the porosity, proton diffusion coefficient, and

electrokinetic permeability ofNafion-1 17 over the temperature range 20-90 OC (F89), and Zawodzinski et al. determined the water uptake and transport properties of the same form of Nafion under polymer electrolyte fuel cell conditions (F90). The effects of water on the diffusional or photoluminescence properties of Nafion films have been reported by others (F91, F92). Cha et al. found that the adhesion of Nafion films to Pt substrates could be improved by an underlayer of an alkanethiol (F93).

Parthasarathy et al. have measured electrode kinetics for 02 reduction at Nafion/Pt interfaces under a wide range of experimental conditions (F94496). Their article describing the results at Nafion-impregnated porous gas-diffusion electrodes gives a brief review of the present status of fuel cell research (F96). Uribe et al. have also measured oxygen reduction kinetics at a Nafion/Pt electrode under fuel cell conditions (3’97). Tafel slopes obtained at gold-coated Nafion membranes indicated that initial 0 2 - formation was the slow step (F98).

The incorporation of small particles into Nafion membranes will often lead to enhanced electrochemical properties relative to the bare metal or an unmodified polymer film. Liu et al., who examined ways to platinize Nafion surfaces, reported that the best method was to impregnate the film with Pt(I1) followed by a borohydride reduction (F99). The oxidation of methanol at metalized Nafion membranes has been further studied (F100, FlOl).

The reduction of aromatic nitro compounds was performed at Pt/Nafion membranes that also served to separate the aqueous counter electrode compartment of the cell from the nonaqueous cathodic compartment containing the substrate (F102).

The partitioning of redox couples between Nafion films and aqueous solutions has been a popular study. Recent examples include a report of supporting electrolyte effects on the partitioning of couples such as O~(bpy)2Clz+/~ (F103) and the effect of oxidation state on the partitioning of U0z2+ (F104). Audebert et al. found that Nafion gels prepared with alkyl phosphates exhibitedselectivity with respect to absorption of organic compounds (F105). The problem of exchange of ions out of ion-exchange polymer-modified electrodes during analysis was alleviated by the expedient of transferring the modified electrode, after preconcentration of ions such as T1+ and Pb2+, from dilute solution into a cell with a solid electrolyte that minimized release of the ions (FlO6, F107).

Electrochemical control of a variety of ion-exchange interfaces other than Nafion films is readily achieved. Zeolite composite electrodes have been used for the oxidation of small molecules (F108) and modified with electroactivecouples such as Ti4+/3+ (F109), Co(II1)-salen complexes (Fl IO), and Ag(I/O) (FI 11). Voltammetry of electroactive species absorbed into clay-modified electrodes has yielded information on the nature of the various clays employed in the studies (FI 12-Fl15). Proton “gating” of the electrochemical response of bilayer clay-modified electrodes containing ion-exchanged sulfonated phenylporphyrin anions was reported (FI16). The overall process mimicked rectifier behavior. An a-cyclodextrin polymer film electrode containing the 4-nitrophenol/4- nitrophenolate guest system had cation-exchange membrane properties (FI17). Kutner and Doblhofer found that the

Analytical Chemistty, Vol. 66, No. 12, June 75, 1994 38SR

release of ferrocenium cations from cyclodextrin film electrodes was dependent on the degree of ionization of fixed carboxylic sites on the polymer (F118) and a poly(pyrrole)/cyclodextrin- modified electrode exhibited some size exclusion selectivity (F119).

Several novel analytical applications of ion-exchange polymer electrodes have appeared in the last two years. A Nafion film electrode was used to preconcentrate a cobaltocenium-labeled amphetamine, acting as a hapten, prior to SWV analysis in a homogeneous electrochemical immunoassay procedure (F120, F121). A dual-electrode FIA/LCEC detector was based on in situ formation of metal complexes formed by the electrochemically controlled release of a pyrrolidine dithiocarbamate ligand from a poly(pyrro1e) film (F122). Nitrosoamine, in the protonated form, was preconcentrated into Nafion-modified electrodes and analyzed by voltammetry (F123). Electrodes modified with quaternized PVP films plus ion-exchanged Fe(CN)64-, Mo(CN)g4-, or IrC163- species were used to preconcentrate and determine Ag(1) (F124), and a hydrophobic poly(dimethyldially1- ammonium chloride) film was used in a three-electrode amperometric oxygen sensor (F125). Electrochemical “transistors” featured gates consisting of protonated PVP, which concentrated electroactive anionic complexes from solution. Drain currents for these species were turned on when the gate was polarized in the Eo’ region for each complex (F126).

It is common for polymer films synthesized from conducting polymer-type precursors or for redox polymers to have ion- exchange properties that dominate their response. Several studies of systems of this nature will be cited, although their classification as ion-exchange, redox, or conducting polymer- modified electrodes is arbitrary in several instances.

Anion-exchange polymer films were prepared by the oxidation of pyrrole monomers substituted in the 3-position with cationic groups (F127) and the oxidation of a pyrrole- substituted pyridinium salt in the presence of 3-methylthiophene (3-MeTP) (F128). A poly(pyrro1e) copolymer with a propanesulfonate arm was permselective to K+ a t low coverage (F1 29), and a poly(o-phenylenediamine) redox film was permselective to I- and Br- (F130). However, PPy films in aqueous acid solution were not permselective to CI- with both K+ and H+ contributing to the charge transport process (F131). FT-IR was used to follow ion incorporation into PPy films containing entrapped dodecyl sulfate anions (F132). Perchlorate ions were excluded, while carbonate ions were slowly incorporated from aqueous solution. For poly(pyrrole)/ poly(styrenesu1fonate) (PPy/PSS) bilayers, EQCM data indicated that oxidation involved cation transport a t low potentials, and anion transport a t high potentials (F133) . Redox cycling of a sulfonated PPy film effected modulation of the surface pH of the film/KCI(,,, interface between pH 5.6 and 8.2 (F134). Anomalous CV reduction peaks in the initial negative-going potential sweep for PPy films in water and CH3CN were shown to be due to cation uptake by the film (F135) .

Ion motion and release by polymer films has been monitored by several different methods including observation of the deflection of a HeNe laser beam a t PPy/solution interfaces (F136, F137). Interestingly, ion transport across the PPy/ solution interface took place both in the faradaic and in the

capacitive potential regions. One group has coined the term “cyclic deflectogram” for these experiments (F138) . Chen et al. used a flow cell with downstream electrochemical detection to verify release of Fe(CN)& from oxidized PPy (F139) and controlled release of ATP from PPy was monitored by UV absorption spectrophotometry (F140).

Nonuniform CdS particles were electrochemically generated and incorporated into PPy/PSS membranes (F141). PPy films containing a tetraaza [ 14lannulene-Cu pendant group were demetalized to produce a film that efficiently extracted metal ions from solution (F142).

UME studies of charge transport in poly(ethy1ene oxide) films have continued to appear (B103, F143-FI46). Other examples can be found in a collection of short papers presented a t a symposium on polymer electrolytes (F147).

For the TCNQ0I-I2- redox couples in PEO, the apparent diffusion coefficients were enhanced by electron transfer between redox partners (F143). Long-range electron transfer a t distances up to 1.6 nm was invoked to explain the data. For the case of a bis(fulva1ene)diiron salt in a low molecular weight poly(ethy1ene glycol)/LiC104 medium, however, physical diffusion dominated electron hopping in the charge transport process (F148). UME steady-state currents of ferrocene in PEO matrices were found to vary with the chain length of the polymer molecules (F149).

Intriguing electroactive ionophores were synthesized by attaching oligo(ethy1ene glycol) chains to tetrathiafulvalene and Co-bpy complexes (F150) . Voltammetry a t very slow sweep rates of the neat room-temperature liquids, which was well-behaved due to the lack of natural convection in the high- viscosity media, was used to determine apparent self-diffusion coefficients.

Voltammetry in COz supercritical fluids was performed using a UME coated with PEO/LiCF3S03 to impart conductivity to the film (F151) . Glassy carbon electrodes coated with Kryptofix-222 gavevery sensitive ( 10-l2 M level) square- wave peaks for the selective determination of Hg in natural waters (F152). Other applications include the direct electron transfer to a ferredoxin a t a phosphatidylcholine-modified Au electrode (F153), the irreversible reduction of retinal at phospholipid-coated Hg electrodes (F154), and the diffusion- controlled CV of amphophilic viologen cations a t lipid electrodes (F155).

In a more theoretical vein, the galvanostatic charging and discharging of a (-)Li/solid polymer electrolyte/porous electrode cell was modeled with a high degree of sophistication (F156). Input parameters for thesimulation included (among others) the diffusion coefficient of Li in the solid matrix, the total concentration in the solid, the conductivity of the solid. the electrode porosity, the exchange current density, and the thicknesses of the separator and the porous composite electrode. Nahir and Buck analyzed the current/time transients, which exhibited potential-dependent, limiting values a t short times, obtained in a chronoamperometric study on PVC membranes containing valinomycin (F157). Their model was based on a fixed-site membrane with a permeable charged species.

Several quite interesting studies with ferrocene polymers have been described. Albagli et al. reported the electrochemical behavior of ferrocene-containing

Ionophore Films.

Redox Polymer Films.


homopolymers and block copolymers that had polydispersities as low as 1.05 (FI58). The oxidative deposition of these polymers from solution depended on the molecular weight and also could be controlled by the size of a nonelectroactive block in the polymer chain. A polymer with a ferrocene- silane backbone displayed surface electrochemistry consistent with two successive oxidation steps, at different potentials, involving fractions of the ferrocene repeat units (FI59). An EQCM study of ferrocene-derivatized siloxane polymer film revealed significant dependence on the anion of the supporting electrolyte (FI60). Electrochemicalcontrolof a polymer phase transition was reported for a novel acrylamide-vinylferrocene copolymer film (FI61). Above and below the phase change transition temperature, the film was either shrunken or swollen, respectively, in aqueous solutions.

Intriguing porphyrin polymers with an alternating one- dimensional structure of oligothiophene electron donor units spaced apart by phosphorus porphyrin electron acceptor units were electrosynthesized (FI62). Photoirradiation markedly increased the conductivity of the materials. Deronzier et al. have reported further on their procedure for electropolymerization of substituted pyrroles possessing electroactive groups such as metallotetraphenylporphyrins (FI63). PPy films were prepared cross-linked by entwined 1,lO-phenanthroline com- plexesofCu(I), Co(II), Zn(II), and Ag(I), which weretethered to the PPy backbone by alkyl spacer arms of variable lengths (FI64). In another intricate variation on this theme, redox- active Fe&d2+ centers were immobilized on L-cystine-derivatized PPy (FI65) . The electropolymerized films were reduced chemically to give ionic pendant cysteinyl(su1fide) groups that ion-exchanged the Fe-S boxes.

Bommarito et al. established that the ratio of Os to Ru in copolymers of poly(viny1bpy) was markedly dependent on the method of polymerization (FI66). In a companion paper, molecular weight and size effects on the transport properties of the metal polymers were investigated (FI67). A photoredox procedure has been devised for the synthesis of poly(viny1bpy)- Ru(I1) films on transparent surfaces (FI68).

Several papers describing the electrochemistry of viologen polymers have appeared (F169-FI72). One of the more interesting concerned the trapping of electronic charge at negative potentials by sulfonated anthraquinone anions that were electrostatically bound to a polymer containing viologen cation units (FI69). The trapped charge could be released by pH change to alkaline conditions, which lowered the quinone Eo’ value, or by the use of redox mediators in solution. The E l p value of the pendant viologen polymer of Katz et al. was dependent on the ionization state of the poly(acry1ic acid) backbone (FI72) .

Other polymer redox films of interest were a poly- (aminonaphthalene) used as a pH sensor for pH of greater than ca. 4 (FI 73), poly(pheny1)s with pendant ethers or poly- (ether)s (FI74), and a quinone polymer film prepared by the electrooxidation of 5,6-dihydroxyindole at glassy carbon (FI 75). Films of electrooxidized 5-carboxyindole were insulating in either the fully oxidized or fully reduced states, but conducting when partially oxidized (FI 76). Redox polymers with a tetrathiafulvalene functionality were based ona poly(thiophene) backboneor a 1,3,5-benzenecore (FI77, F178). In the former case thevoltammetry was a superposition

of that of the TTF and PT units. Thio-substituted quinones adsorbed on Au and Pt(Hg) provided a simple means of modifying electrode surfaces (FI 79).

Redox polymers with molecular weights up to 20K were covalently attached to Pt, ITO, and n-Si electrodesvia siloxane bonds at one end of the polymer chain. The interface structure was disordered, as indicated by the surface coverages which were only 2% of that of a close-packed monolayer of alkanethiols (FI 80).

Prussian Blue and films continue to attract attention as exemplified by the long-term stability study of Stilwell et al. (F181). The pH of the electrolyte solution was the critical factor, with redox cycle lifetimes greater than los easily achieved for pH 2-3. The voltammetry and chronoamperometry of thin films of silver ferricyanide featured asymmetric CVs and exponential current decay (FI82). Kulesza et al. carried out Prussian Blue voltammetry in the absence of liquid electrolyte using a simple two-electrode, large glassy carbon/UME configuration (FI83). Other studies of similar systems have been published in the last two years (FI84-FI89).

Electrochromism and Pattern Formation in Polymer Electrodes. There have been several advances in the related areas of electrochromics and pattern formation at modified electrodes. Since these applications tend to cut across the ordinary lines of classification for modified electrodes, they will arbitrarily be collected into a separate section.

Yoneyama and co-workers have produced impressively high quality light image formation in a poly(ani1ine) (PAn)/TiO2, PAn/TiOz, film (FI90, F191). A poly(ani1ine) image of a human subject is shown in the publications from Yoneyama’s laboratory. Illumination of the film was performed in pH 7 phosphate buffer containing methanol as a hole scavenger under conditions of low PAn conductivity to prevent image spreading. The yellow images of reduced PAn were easily erased by polarizing the films at 0.5 V vs SCE. Images in metal-bpy polymer films were also produced by a combination of photochemistry and electrochemistry (FI92). In this case, a spatially controlled image of the original mask was produced. Poly(ani1ine)-methylene blue-Nafion composite film electrodes, which had been further modified with Ru(bpy)32+, developed images upon illumination (FI93).

In another approach, procedures were given for the photoproduction of very small, patterned tungsten nuclei in a microlithographic resist consisting of phosphotungstic acid and poly(viny1 alcohol). The nuclei served as nucleation sites for the subsequent electroless deposition of Ni. Features with dimensions on the order of 0.3 pm were formed (FI94).

Another method for creating microstructure and patterned images in polymer films involved photochemical ligand loss from metal redox polymer films containing tetramethyl-bpy complexes of ruthenium. The photochemical reaction created “voids” that could be filledvia reaction with osmium phosphine complexes (FI95). Brumfield et al. also created patterns in polymer films by deposition of conducting polymers into defects that had been formed in insulating films with an AFM tip (E280).

A novel display device was based on the pH change, induced by the oxidation of a PPy film in NaCl(,,), that caused a reversible flocculation of a poly(L-lysine) microgel (Fl96).


Instantaneous detection of light intensity changes and image production were achieved with a 64-element array contacting a bacteriorhodopsin film on a Sn02-transparent electrode (F197). SEM was used to detect images formed in irradiated self-assembled monolayers containing photoactive aryl azide groups (F198). Micropatterning of PPy on insulating surfaces was performed by growing the conducting polymer film across surfaces that were hydrophobic (F199-F201). A maskless local deposition procedure was based on the electrodeposition of poly(ani1ine) a t laser-irradiated sites (F202).

Papers describing modified electrodes with good electrochromic properties continue to appear. Recent examples include L-B films of several rare earth bis(phtha1ocyanine)s (F203), Cu and Ni phthalocyanine films (F204), poly- (viologen) films (F205), poly(vinylo1igothiophene) (F206), poly(quino1inium) salts (F207), and poly(aniline)/W03 composite films (F208, F209). Related to this application is the report of a procedure for growing a poly(thiophene) film that was transparent in the visible region for both the oxidized and reduced states (F2I0) . Siekierski et al. also described a poly(thiophene) that was highly transparent in the conductive state (F211). The electrochromic specifications of a PPy/ Prussian Blue/KzS04(aq), poly(benzylvio1ogen) system were especially impressive (F212).

Light emission from conjugated polymers of the poly@- phenylenevinylene) type, which has been reported by several laboratories (F213-F215), represents an intriguing approach to large area displays. The flexible LEDs of Gustafsson et al. were fabricated from free-standing films of poly(ethy1ene terephthalate) as a substrate, PAn as the hole injecting contact, an electroluminescent layer, and a calcium metal negative electrode (F215). Greenham et al. achieved quite high efficiencies with poly(cyanoterephtha1ylidiene) LEDs-up to 4% photon out per electron injected (F216). For the sandwich cell, Al/poly(thiophene)/ITO, light emission was seen at applied voltages of 10 V (F217). Photoluminescence intensity and wavelength from poly(3-hexylthiophene) was dependent on the regioregularity of the polymer chain (F218).

Recent work on electrochemical aspects of electronically conducting polymers, e.g., poly(pyrrole), poly(aniline), poly(thiophene) (PT), etc., will be reviewed here. The equally vast literature on the solid- state physics of these and related systems will not be covered.

Synthetic Aspects. Radical cation coupling reactions have been suggested as the carbon-carbon bond formation steps for several pyrroles (F219) and for 3-MePT (F220) based on double-potential step chronoamperometric and spectroelectrochemical data, respectively. RRDE and EQCM techniques have also been employed to good effect to distinguish between coupling mechanisms and to identify intermediates in the electrosynthesis of conducting polymers (F221, F222). Elec- tropolymerization of pyrrole in the presence of a N-meth- ylphenothiazine mediator proceeded via a catalytic scheme (F223).

STM images and in situ video recording of the nucleation and growth of 3-MePT were reported (F224, F225). The electropolymerization and deposition process of PT-3-acetic acid was concluded to proceed via a two-dimensional layer- by-layer nucleation mechanism (F226, F227). The fast CV study of Vuki et al. (B63) indicated that, a t room temperature,

Conducting Polymer Electrodes.

the growth of PAn nucleation centers, and not slow electron or counterion motion, limited the current. At low temperature, ion transport controlled the current a t long times. Perhaps related to this is the observation of spatial variation of the PAn conductivity, on the order of 20-30 nm, corresponding to granular metallic regions (F228).

Several papers have addressed the question of the molecular weights of electrosynthesized polymers. Wei and Tian found that the applied potential influenced the molecular weight of electrosynthesized 3-alkyl-PT (F229). The molecular weight exhibited a maximum of greater than 50K at an intermediate potential (1.6 V vs SCE) and was lower in the presence of additives such as 2,2'-bithiophene. The molecular weight of electrosynthesized PAn, which was less cross-linked than the chemically synthesized material, was estimated to be greater than 50K (F230). Also low-temperature (0 "C) was found to give increased doping levels and conjugation lengths for PPy electrosynthesis (F231). Photocurrent spectroscopy a t IT0 electrodes provided evidence that the first traces of electrosynthesized 3-MePT had long conjugation lengths (F232).

Two reports have described the effect of sweep rate on the morphology of PAn films: fast sweep rates (20 V/s) gave the more uniform dense films (F233, F234). Ellipsometry and EQCM data indicated that a periodic cathodic bias during anodic growth of PAn resulted in morphological changes characteristic of increased long-range order (F235). p - Phenylenediamine increased the rate of PAn electropolymerization and altered the morphology of the resulting film (F236).

Improved yields were obtained for the electropolymerization of thiophene in the presence of ultrasonic waves (F237).

Electropolymerization of pyrrole from aqueous carbonate solutions produced pinhole-free insulating films, ca. 100-300 nm thick (F238). Two groups have studied theoveroxidation and degradation of PPy (F239, F240), and the deactivation of 3-MePT in the presence of C1- was partially restored by oxidationinCH3CN (F241). In thelattercase, thereactivated film was chlorinated. Conditions were given for the electrosynthesis of brominated PPy (F242), and PPy films have been grown in the presence of zwitterionic buffers (F243).

3-MePT conducting fibers as long as 10 cm were grown in a capillary flow cell where the fluid flow pattern, in part, governed the shape and diameter of the fiber (F244). Especially interesting was the fabrication of flexible, conductive composite fibers by electrolysis along the surface of polyester and Kelvar strings attached to the electrodes (F245). PAn has been grown on nylon and glass cloth via chemical oxidation of aniline-permeated substrates (F246), and PPy electrosynthesized in a nematic liquid crystal medium exhibited only slightly anisotropic conductivity and no evidence of crystallinity (F247) . Several papers have described the synthesis of PPy either on Ta or within the pores of sintered Ta electrodes

A wide variety of different conducting polymer films have been electrosynthesized. Recent interesting examples include highly anisotropically conducting films produced by the electroreduction of a soluble naphthalenedicarboximide in the presence of a polycation (F251), films of electropolymerized thiophene, bithiophene, and terthiophene in the presence of Keggin heteropolyanions (F252), poly(o-anisidine) (F253),

(F248-F250).


and poly(o-toluidine) (F254). Let it be noted that 1992 was a good year for the electrosynthesis of poly(parapheny1ene)

Several studies have appeared on the electrosynthesis of bickey ball films (8'2634265). Jehoulet et al. found that films fully reduced to a (260- state were poor electronic conductors, while partially reduced films displayed enhanced electronic conductivity (F263). Reduction took place with a large structural reorganization and intercalation of the supporting electrolyte cation.

Electrochemical Characterization. There have been several spectroelectrochemical studies ofoligothiophene molecules with four to eight thiophene units linked at a-position. These molecules exhibited EE behavior coupled to a-dimer formation of the radical cation to form a diamagnetic species (F266- F270). A significant aspect of this observation is that the a-dimer dication, and the corresponding a-dimer radical cation, are possible alternative structures for the bipolarons and polarons, respectively, in "doped" organic metals of the PT type. The sexithiophene CVs obtained by Bauerle et al. (F270) revealed a 2+/+/0/-/2-/EEEE system with a 2-V separation between the anion and cation formation waves. Xu and Horowitz boldly predicted the chain length of PT by comparison of its oxidation potential to an extrapolated value obtained for oligomers with four to six thiophene units (F271). Guay et al. have also looked at thiophene oligomers with up to seven thiophene rings (F272-F274). For molecules with orthogonally fused thiophene oligomers, there was no indication of a-dimer formation in the oxidized forms.

A very nice comparison of the electrochemistry of a conducting polymer as a thin film and in solution was made by Jozefiak et al. on high molecular weight-substituted polyacetylenes (F275). The thin-film voltammetry of these molecules was well-behaved, showing oxidative and reductive doping steps separated by ca. 2 V. The cis-polyacetylene film voltammetry was irreversible indicating rapid cis to trans isomerization following electron transfer. In contrast, the solution CVs did not exhibit well-defined peaks, which the authors attributed to multiple, highly coupled redox states having a greater degree of conformational and rotational freedom than in the solid state.

Only a few of the many studies on the electrochemical redox switching of conducting polymer films will be mentioned here. The CV and ac impedance study of Duffitt and Pickup on PPy indicated that a nonequilibrium state of PPy containing excess electrolyte and solvent was formed upon reduction and reoxidation of PPy in CH3CN (F276). Changes in the ionic resistance of the films were explained by slow transport of salt and/or solvent out of the films. Son and Rajeshwar reported a significant role for 0 2 in the redox switching of PPy. In the presence of oxygen there was a direct transition to a bipolaron state, while in a nitrogen atmosphere a neutral to polaron to bipolaron transition was observed (F277). Van Dyke et al. showed that the insulator to conductor transition for PPy could be extended by ca. 0.7 V in the negative direction by treatment of the PPy films with degassed NaOH solution (F278). The effect was rationalized by the relative affinities of the PPy cationic sites for OH-and BF4- ions. Spectroelectrochemistry of 3-MePT indicated that two redox processes were operative for the formation of radical cation(po1aron) and dication-

(F255-F262).

(bipolaron) states, both of which were shown to be charge carriers (F279). (See the Accounts of Chemical Research article by Tolbert for a good molecular-based view of the chemical basis for conductivity in organic metals (F280) ,)

Differential pulse voltammetry of a novel electrically conductive butylphthalocyaninato silicon polymer was interpreted in terms of the bandwidth and structure of the solid- state molecular orbital (F281). The two DPV peaks were correlated with maxima in the'density of states of the valence band.

Theory for conducting polymer voltammetry incorporated the Butler-Volmer equation in order to take into account slow electron transfer at the polymer/metal interface (F282). Doblhofer argued that, since the potential of solvated conducting polymer systems such as PT remains relatively constant as they are oxidized, they are best described as redox polymers (F283).

Several interesting experimental and theoretical treatments of the pH-driven conductor to insulator transition for PAn films have appeared. Donnan potential expressions and electroneutrality were employed to explain the pH dependence of the transition for PAn and PAn/poly(vinylsulfonate) mixtures and the effect of NaCl concentration on the conductivity of emeraldine films (F284, F285). Another treatment of the PAn protonation equilibria required only one apparent pK, value (ca. 5 ) to account for the experimental conductivity/pH curve (F286). Theory for order-disorder transitions in binary alloys was applied to benzenoidquinonoid and quinonoidquinonoid segments in PAn (F287), and a model for PAn oxidation and protonation was presented that accounted for the interactions between the positively charged protons and polarons in a one-dimensional chain (F288). On the experimental side, EQCM of PAn revealed significant mass changes only in the pH interval between 1 and 3 where the reduced form is practically unprotonated and the half- oxidized form is protonated (F289).

Applications. An informative review of the use of conducting polymer electrodes in batteries has appeared in which fundamental problem areas with regard to com- mercialization were identified (F290). PPy and poly(N- methylpyrrole) have been compared with an eye to use as a positive electrode. The latter material cycles 0.6 V more positive than PPy, but loses Coulombic capacity upon cycling (F291). Gravimetric charge densities up to 270 A h kg-l were determined for PAn in propylene carbonate/LiClOp solution (F292).

The incorporation of metal particles into conducting polymer films has been a strategy explored for a variety of electrocatalytic applications. Recent examples include Pb02/ PPy (F293), Pt/PAn (F294), Pd/(PAn or PPy) (F295), and Pt/PPy (F296, F297) composite film electrodes. A good exampleis thearticleof Chen et al., whostudied the permeation of H2 and 0 2 into composite films of PPy containing nanometer-sized Pt particles (F297). Conditions for the preparation of PPy films containing homogeneous distributions of W03 and 0.4-pm Ti02 particles have been given (F298, F299).

Two interesting applications of conducting polymers as membranes stand out. Martin and co-workers reported that oxidized PPy membranes, supported in the pores of a


polycarbonate membrane, could transport electrons across the membrane between a donor/acceptor pair, while simultaneously transporting ions to maintain charge neutrality (F300) . More interestingly, they also demonstrated that glucose oxidase could exchange electrons with the membrane and drive the oxidation of glucose in a transmembrane manner. Nafion/PAn and free-standing PAn membranes have been used as porous gas diffusion membrane electrodes for the oxidation of SO2 and N2H4, and for the reduction of NO2 and

The volume change that takes place when polymer films are redox cycled is the basis for possible servomechanical devices, in which a conducting polymer film is firmly attached to an electroinactive substrate, e.g., commercial adhesive tape in one example (F302) . The curvature or bending of such strips has been studied by several groups (F303-F305). The dimensional changes, driven by proton or redox doping, were largely reversible for PAn films; values of percent elongation up to ca. 10% were reported for oriented films in the perpendicular direction to the draw axis (F305). A velocity of 5 X m/s was reported for the propagation of the oxidized zone on a PAn strip (F306).

Conducting polymer diodes and transistors are other curiosities that continue to attract attention. McCoy and Wrighton configured two conducting polymer “gates” as a push-pull amplifier such that there was no crossover distortion when the output current went through zero (F307). Fox discussed ways to control directional charge transport in electroactive polymer arrays, including some voltammetry on PT/PPy and PPy/PT bilayers (F308) . Buck et al. have discussed the analogies and differences between liquid/solid polyelectrolyte diodes and conventional solid-state semiconductor diodes (F309) . They gave conditions for the chemical mimicking of p-n junctions involving ion-exchange and redox polymers. The experimental study of Han et al. on Nafion bilayers supported their ideas (F310). These workers reported diode behavior for a Nafion bilayer prepared by sandwiching two films together at 150 OC in a mechanical press-one film was loaded with F e ( ~ h e n ) 3 ~ + , and the other with Fe- hen)^^+/^+. Others have reported diode-like behavior for junctions such as poly(bithiophene)/Si and PPy/poly- (p-phenylenevinylene) (F31 I ) .

Chemically deposited PPy has been used as a precoat for the metalization of printed circuit boards (F312) . Electro- deposited PPy on carbon fibers improved the bonding between the fibers and an epoxy resin matrix (F323).

The surface chemistry of self-assembled monolayers, especially of alkanethiols bonded to well-defined gold surfaces, is a field to itself which has blossomed in the last decade. The ability to manipulate interfacial structure via the chemistry of SAMs is unprecedented. There are now a significant number of modified electrode studies in which the interface exhibits novel phenomena due to its microstructure in either the lateral or perpendicular direction.

Several research groups have addressed the question of how the potential gradient across a SAM affects charge transport and the voltammetric response at a SAM-modified electrode. Smith and White showed that non-Nernstian wave shapes were a function of the thickness and dielectric constant

0 2 (F301) .

Self-Assembled Monolayers.

of the film, the surface concentration of the adsorbate, the supporting electrolyte, the solvent dielectric constant, and the Epzc (F314) . Correction procedures that take into account the potential a t the “plane of electron transfer” were described that are similar to Frumkin $2 corrections for irreversible electron-transfer reactions. The electric field strength in a SAM at a roughened Ag electrode was measured by observation of the Stark effect on the fluorescence spectra of a dye molecule in the film (F315) . A value of ca. 4 X lo4 V/cm was found at a point in the diffuse region of the double layer. The nature of a SAM interface was also probed by measurement of redox potentials of viologen groups positioned a t different locations with respect to the interface. One conclusion of this study was that hydration of the viologen dication was the principal factor in determining the Eli2values (F316) . Kitamura reported spike-like voltammetric peaks, indicative of attractive interactions in the adsorbed state, were dependent on the alkyl chain length for N,N’-dialkylviologen cations a t Hg electrodes (F317) . Creager and Weber calculated the effect of ions on the potential distribution, and the resulting effect on electron-transfer rates, across a monolayer (F318) .

Electron tunneling through thiol SAMs a t gold electrodes has been a popular topic. Becka and Miller reported that the tunneling coefficient, 1.08 f 0.20 per CH2 group, was almost independent of the potential and the redox couple in solution (F319) . On the other hand, for redox molecules as different as ubiquinone and Fe(CN)63-, Takehara et al. found a marked difference in the effect of n-alkanethiol SAMs on the electron- transfer kinetics (F320) . A careful and detailed study of electron-transfer kinetics of pentaammine(pyridine)Ru complexes tethered to gold via an alkanethiol linkage provided evidence for the existence of a small fraction of fast electron- exchange centers that dominated the currents a t low overpotential (F321). Analysis of the data for molecules with (CH?)lo-l* tethers suggested that through-bond tunneling, as opposed to through-space tunneling, was the mechanism of electron transfer. Curtin et al. also investigated the effect of the length of the tethering arm on the low-temperature CVs obtained on ferrocene thiol SAMs (F322) . The influence of film thickness on electron-transfer rates was very clear for an electrode covered with multilayer films of a metal phosphonate structure (F323) . Obeng et al. reported “b1ocking”properties of rigid rod thiols on Au (F324) . In other studies Finklea and co-workers obtained nearly ideal CV surface waves for electroactive thiols containing pendant p y R ~ ( N H 3 ) 5 ~ + / ~ + redox centers on gold electrodes (F325, F326) .

Electrodes modified with self-assembling molecules with terminal acid/base or ionic groups can enhance or suppress selected electrode reactions, depending on the state of the end group. For example, rates of cationic couples such as R u ( N H ~ ) ~ ~ + / ~ + and anionic couples such as Fe(CN)63-/4- a t SAMs with terminal ionic groups were affected in markedly different ways by solvent effects (F327). The effect of pH on the response of SAMs has been reported for the latter couples a t thioctic acid-coated electrodes (F328), for Fe(CN)63-/4- at 4-pyridyl sulfide electrodes (F329) , and for carboxylic thiol SAMs on a QCM surface (F330). SAMs of HS(CH2),C02H on Au discriminated against ascorbate anions in the voltammetric analysis of dopamine, with n = 5 giving the optimum differentiation (F331). Related to these studies


is the prediction that maxima and minima will appear in i-E curves of molecular films containing acid/base groups that are due to variations of the differential capacity (F332).

Activity and ion-pairing effects have been noted at SAM modified electrodes. For the ( N H ~ ) ~ R u ~ + / ~ + couple attached to Au in an organized monolayer, activity coefficient effects were consistent with a model in which one anion was transferred between solution and the metal center in the monolayer for each electron transferred (F333). (This paper also contains a good example of the influence of liquid junction potentials on measured electrode potentials.) Ion-pairing effects were invoked to explain the very rapid electron-transfer kinetics of a SAM of a redox-active Os(III/II)-bpy complex (F334) and for the (ferrocene)+/Ocouple in an n-alkanethiol SAM (F335).

The lateral diffusion of octadecylferrocene in a L-B bilayer assembly was found to be dependent on the fluidity of the monolayer film (F336). In a previous paper Majda and co- workers documented the transition between two-dimensional diffusion and steady-state mass transport for the microband voltammetry of CIS-ferrocene surfactant films (F337). Katz et al. reported that treatment of disordered viologen films, in which ester links were in the tethering arms, with Cl&H produced distinctly ordered behavior (F338). Mixed monolayers of Cl&H and ClsOH have also been characterized electrochemically using ubiquinone probe molecules (F339),

Reductive desorption of alkanethiols on evaporated Au surfaces was the basis of a method reported for the measurement of thiol surface coverage (F340). Porter and co-workers have also observed the potential controlled electrodeposition and stripping of alkanethiols in ethanolic KOH (F341).

Nanoporous SAMs on Au were prepared by spontaneous adsorption of two thiols from solution. The structure and electrochemical response of the interface could be manipulated by variation of the ratio of the thiols and their nature (F342). Cyclic voltammograms were obtained at a L-B interface containing 8-cyclodextrin channels using the “horizontal touch method” (F343). Inhibition of the electron-transfer process for permeable species was seen when uncharged electroinactive guest molecules such as cyclohexanol were present in solution. A laser desorption procedure was described for the preparation of mixed thiol monolayers that functioned as “ion-gate” interfaces (F344). Kim and Bard were able to form pits and aggregates in alkanethiol SAMs by control of the bias voltage, the tunneling current and the position of a STM tip (F345).

Gold electrodes treated with cystamine were further functionalized by treatment with trans-stilbene diisocyanate. This produced a reactive surface for attachment of redox proteins and other electroactive groups (F346). Lu et al. published CV evidence for one of the more intricate of modified electrodes with a covalently attached donor/acceptor catenane complex (F347). The procedure involved attachment of both terminal thiols of substituted aromatic donor “needle” molecules to the electrode surface. Other interesting modified electrodes include the L-B films of rigid rod oligoimides and thiol-terminated SAMs of oligoimides of Miller and colleagues (F348, F349).

The &/trans isomerization of a single L-B monolayer of a polymeric azobenzene was followed after irradiation using a “displacement current” technique (F350). (In this method, the cell consists of two parallel electrodes where one is in air

ca. 1 mm above the surface of the L-B film.) A CV study of this isomerization over the temperature range 3-41 “C has also appeared (F351). This system is the basis of coulometric actinometer since the more easily reduced cis form of the azobenzene can be quantified using Faraday’s law (F352- F354).

Several groups have studied electron transfer to biologically important molecules such as cytochrome c at SAM-modified electrodes (F3554358) . These and related interfaces have been touted as ideal physiological membrane-mimetic systems for the study of redox proteins (F355, F359).

A hydrophobic hydrogenase enzyme was immobilized in a bilayer assembly containing CIS-viologen as an electron mediator (F360). Efficient coupling of the enzymatic activity to the electrodesurface was realized using both potentiometric and steady-state voltammetry. Mediated electron transfer to the redox enzyme glutathione reductase covalently attached to a cysteic acid ester monolayer was achieved by reaction of the SAM/enzyme surface with a viologen mediator (F361).

Reports of molecular diode-like behavior have appeared. SAMs of a u-substituted ferrocenyl alkanethiol on gold were shown to exhibit unidirectional electron transfer in the presence of the Fe3+/2+couplein water (F362). The monolayer surface mediated reduction of Fe3+, but inhibited the oxidation of Fe2+. Asymmetric i-E curves indicative of “molecular rectification” were also obtained for L-B sandwich cells containing a donor/acceptor surfactant molecule (F363) and for a flavolipid/cytochrome c heterolayer prepared by L-B techniques (F364).

Several miscellaneous studies were noted. Thevoltammetry of L-B films of phospholipids functionalized with anthraquinone groups revealed anion effects related to the supramolecular structure of the monolayers (F365). Reduc- tive dechlorination of an aryl chloride was carried out in a cationic surfactant film (F366). The CV behavior of simple cations at phosphatidylserine-coated Hg electrodes was markedly pH dependent. These films were relatively impermeable to cations (e.g., T1+ or Pb2+) at low pH or in the presence of strongly bound ions such as La3+ (F367). Electron-transfer rates of amphiphilic ferrocene-substituted surfactants in cationic micellar media indicated that the molecules were oriented with cationic headgroups toward the electrode surface (F368). Disordering effects were deduced from a CV study on SAMs of a cholesteryl viologen (F369). Salt formation was indicated for redox cycling of bis(phtha1ocyaninato)- Yb(II1)-stericacid L-B films (F370). Formation of a porous deposit was indicated when methylviologen was reduced on glassy carbon electrodes in the presence of sodium alkyl sulfate surfactants (F371). A two-capacitor model was advanced to explain double-layer capacity data obtained at thiol-coated Au electrodes (F372).

Electrochemistry in gel matrices has been the subject of several interesting studies. Rillema et al. performed photochemistry on the R ~ ( b p y ) 3 ~ + / viologen system in a hydrogel matrix where the diffusion coefficients were only 1 order of magnitude smaller than in aqueous environments (F373). A sol/gel Si02 film doped with R ~ ( b p y ) 3 ~ + was ceramic in nature and porous enough to allow electron transfer to the electrode substrate (F374). Electropolymerization of aqueous solutions of acrylamide gave

Other Modified Electrodes.


thin poly(acry1amide) films on carbon fiber electrodes with number-average molecular weights up to 430 000 (F375). The reversible, cooperative complexation of surfactants in a polymer gel was the basis of a device that converted electrochemical energy into mechanical energy (F376).

Modified electrodes with permselective and electrocatalytic properties were prepared by casting cellulose acetate films, which had been hyrolyzed in base to provide porosity, over electrodeposited Pt and Pd surfaces (F377). Christie et al. found that poly(viny1 chloride) gave better selectivity than cellulose acetate as a barrier membrane in amperometric sensors for H202 and phenolics (F379).

G. B I OELECTROCHEM I STRY Books and Reviews. Smyth wrote a new book that surveys

the voltammetric analysis of a large number of small organic and inorganic molecules of biological importance (GI). Schultz and Taniguchi edited the proceedings volume for the Fifth International Symposium on Redox Mechanisms and Interfacial Properties of Molecules of Biological Importance, held in May 1993 (GZ). This is an excellent collection of richly diverse, high-quality papers that give a clear sense of the state of bioelectrochemistry as of 1993. The electrochemistry and spectroelectrochemistry of proteins, enzymes, small molecules, membranes, and cells, as well as new concepts and techniques, are covered. Volume 221 of the Methods in Enzymology series will be of great interest to metalloprotein chemists as it covers physical and spectroscopic methods for probing metal ion bioenvironments. Of special interest to electrochemists are the three chapters by Stankovich and co- workers on EPR spectroelectrochemical titrations of redox enzymes (G3), Armstrong and co-workers on the voltammetry ofadsorbed metalloproteins (G4) , and Hill and Hunt on direct and indirect enzyme electrochemistry (G5).

A brief yet succinct overview of the electrochemistry of biopolymers (proteins, polynucleotides) was provided by Cox and Przyjazny (G6). Ewing et al. discussed aspects of performing analytical chemistry (electrochemistry, separations, identification) in microenvironments, specifically single nerve cells (G7). The roleof voltammetric methods in research and development of pharmaceuticals was reviewed by Kauff- mann and Vir6 (G8). Volk et al. discussed the application of electrochemistry/mass spectrometry for the elucidation of biological redox mechanisms (G9).

Many reviews and some books relating to amperometric biosensors were published over the past two years. In several excellent reviews, the crucial issue of coupling enzymatic reactions to current-carrying electrodes was addressed authoritatively. Encompassing reviews regarding enzyme/ electrode coupling were provided by Ikeda (GIO) and Bour- dillon (GI!). Gorton et al. reviewed the topic of biosensors based on apparent direct electron-transfer reactions of peroxidases (GI2). In another very informative review, Heller reviewed his and others’ work on redox “wiring” of enzymes to electrodes (G13). Redox “wiring” was also covered by Boguslavsky et al. in their article, which was more narrowly focused on ferrocene-derivatized siloxane and ethylene oxide polymers (G14).

A very timely review article on glucose oxidase, with an emphasis on properties important to biosensor development,

was published by Wilson and Turner ( G I 5 ) . A general biosensor review was given by Ivnitskii et al. (G16), which included reference to numerous Russian language papers. Hilditch and Green reviewed the topic of disposable electrochemical biosensors and discussed requirements that are needed for commercial viability (GI7).

Several books on biosensors that include chapters on amperometric sensors were recently published, but your reviewer has, regrettably, yet to examine them except for Table of Contents listings. Among these is the second volume in the Adcances in Biosensors series edited by Turner ( G I 8 ) . This volume appears to contain a number of chapters of interest to amperometric biosensor scientists. Another book, edited by Nakamura et al., is concerned with immunochemical assays and biosensors (GI 9) and includes two chapters on amperometric biosensors and electrochemical immunoassay.

The use of chemically modified carbon-type electrodes was reviewed by Wring and Hart (G20) with an emphasis on mediation reactions in biosensors.

Bilayer lipid membranes were reviewed for electrochemical sensing applications by Nikolelis and Krull (GZI ) and for bioelectronic devices in a comprehensive review of BLMs by Ottova-Leitmannova and Tien (C22).

Small Molecules of Biological Importance. Our ability to efficiently oxidize and reduce small biological molecules a t electrode surfaces carries important ramifications. From a biochemical perspective, this ability opens the way for powerful investigations of the redox energetics and dynamics of these molecules in the context of biological function. From an analytical perspective, efficient redox conversion obviously provides a basis for sensitive voltammetric or amperometric detection of the molecules per se. Furthermore, for those particular molecules serving as enzyme cofactors, their electrodic behavior can assume paramount importance with regard to designing amperometric biosensors. Because many small molecules of biological importance are organic species, they typically do not undergo clean facile electron-transfer reactions a t metal electrodes. Large redox overpotentials and electrode fouling tend to be standard fare, and thus, numerous investigations over the years have sought to minimize these factors through mediation and electrocatalytic strategies. This trend continued during the past two years. In the coverage that follows, we have not included studies of pharmaceuticals or investigations of complex chemical reactions coupled to electrolysis. Our emphasis is decidedly interfacial. Porphyrin- modified electrode studies directed toward catalysis of 0 2 are also not included.

Substantial interest continued with regard to the electrochemistry of nicotinamide adenine dinucleotide (NAD/ NADH). The oxidation of NADH is a pivotal component in the design of dehydrogenase-based enzyme electrodes. Typi- cally, however, unmediated NADH oxidation proceeds a t large overpotentials with comcomitant electrode fouling. Kuhr et al. described a most interesting and potentially useful CV study of NADH oxidation at carbon fiber microelectrodes (G23). By using judicious electrochemical pretreatment (to minimize NADH adsorption) in combination with fast 100 V/s scan rates (to minimize electrode fouling), reproducible electrooxidation of NADH was achieved at bare carbon fiber surfaces. The application of this approach to the development


of hydrogenase-based microelectrodes was also considered. In past years, some very successful mediators have been developed by Gorton and others specifically for NADH oxidation. Perhaps the best one, Meldola blue, was incorporated successfully by Hale et al. into a siloxane polymer structure that is easily deposited on electrodes by evaporation (G24). A more complicated approach to the mediated oxidation of NADH involves the incorporation of a second enzyme, e.g., diaphorase, specifically to oxidize NADH, with the mediator then oxidizing thediaphorase (G25). Yet another potential solution to the problem at hand is direct electrocatalytic oxidation of NADH on electrochemically grown conducting polymers, although few have been found to date that function in this capacity. Two promising candidates were reported on, namely, poly(indo1e-5-carboxylic acid) (G26) and poly(thionine) (G27).

Reduction of NAD+ to NADH, also a difficult reaction, is important synthetically in bioreactors but less so from an analytical standpoint. The incorporation of rhodium complexes in polymer film electrodes resulted in the catalysis of this reaction with good selectivity for 1 ,4-NADH and without the formation of NAD dimers (G28, G29). Catalyticreduction of NAD+ by hydrogenase at platinum electrodes was also described (G30).

Basic electrochemical investigations of catechols and catecholamines on carbon-type electrodes emphasized voltammetric discrimination capabilities. Such studies are of direct relevance to in vivo neurochemical studies, which are reviewed under In Vivo and Cellular Electrochemistry. Tokuda and co-workers investigated the effects of electrochemical pretreatment on the oxidation of dopamine (DA) (G31). Discrimination against DOPA and DOPAC, but not ascorbic acid, can be achieved by employing a "mild" pretreatment. Caution against the indiscriminate use of "strong" pretreatments for DA detection was given. Over the last few years, McCreery's group has provided much valuable insight into carbon electrode voltammetry. Of relevance to this section is a detailed investigation of theirs concerned with the adsorption of catechols on glassy carbon surfaces (G32). Whereas DA, 4-methylcatechol, and DOPAC all adsorb strongly on fresh-fractured GC, the interaction is weak on polished surfaces apparently due to impurity adsorption. Electrochemical pretreatment leads to adsorptive preference for DA, a cation, due to oxidation of the GC surface. Reverse differential-pulse voltammetry was used by Matysik et al. in a study aimed at discriminating among a serious of catechols (G33). Nafion coatings are frequently used with carbon electrode studies of neurotransmitters to electrostatically discriminate against ascorbate and other anions. A new electrostatic approach was described by Malem and Mandler in which COOH-terminated alkanethiolate self-assembled monolayers on gold were effective in discriminating against ascorbate during the detection of DA (G34).

The direct oxidation of carbohydrates, alcohols, and amino acids is now performed routinely at noble metal electrodes due to the efforts of Dennis Johnson and co-workers. In the latest chapter, Vandeberg and Johnson report on the pulsed electrochemical detection of the sulfurous compounds cysteine, cystine, methionine, and glutathione, at picomolar detection limits (G35). Lacourse and Johnson have described an

automated optimization of all waveform parameters for the pulsed amperometric detection of several representative carbohydrates (G36). Wang's group has been developing chemically modified electrodes for HPLC and FIA determination of various biological compounds. Accounts were given of the design and characterization of a Prussian Blue electrode for glucose detection (G37) and a polymer film electrode containing nickel (0xy)hydroxide catalyst for carbohydrate and amino acid oxidations (G38). The oxidation of glucose can also occur readily at organic conducting salt electrodes as shown by Zhao and Lennox for TTF/TCNQ (G39). Electrodes based on HMTTeF-TCNQ (where HMT- TeF represents hexamethylenetetratellurafulvalene) (G40) exhibited especially good versatility for a number of other important oxidations including glutathione, cysteine, dopamine, and ascorbate. This latter electrode is considerably more resistant to dissolution than TTF/TCNQ. These and other papers from this group shed considerable light on the biological oxidations that occur at organic conducting salt electrodes.

The interaction of amino acids with copper has also been examined electrochemically. Weber's group, in efforts to develop detection schemes for nonelectroactive peptides, have exploited the biuret reaction, which produces electroactive Cu(I1)-peptide complexes. The influence of tyrosine, an electroactive amino acid, on the electrochemical response was addressed in a recent report (G41).

An amperometric sensor was described by Malinski and Taha for the detection of nitric oxide (G42), a molecule whose biological importance has only begun to be appreciated in the past few years. This sensor, which is constructed by electropolymerization of a Ni-porphyrincatalytic filmon a carbon fiber electrode, had a detection limit of 10 nM. Furthermore, it was sufficiently miniaturized, 0.5-m fiber diameter, to monitor N O release from a single cell.

Several other important molecules were the subject of significant investigations. The electrochemistry of the co- enzyme pyrroloquinolinequinone (PQQ) was found to be reversible under acidic conditions at bis(4-pyridy1)disulfide- modified gold electrodes (G43). The oxidation of biliverdin, a key intermediate derived from bile metabolism, was examined by thin-layer spectroelectrochemistry and its formal potential was reported (G44). Hemin adsorbed on pyrolytic graphite electrodes was examined in-depth by UV/visible electroreflectance (G45). The adsorption and voltammetry of ubiquinones was examined at the mercury electrode (G46).

Flavins and related compounds were explored electrochemically in both solution and monolayer formats. Verhagen and Hagen described somevery nice electrochemistry of flavin adenine dinucleotide (FAD) at glassy carbon electrodes (G47). High electron-transfer rates were measured for adsorbed FAD, which appeared to act as a surface mediator for the subsequent reaction of diffusing FAD. The electrochemical behavior of solution FAD (and also a ubiquinone) was examined by Takehara et ai. at gold electrodes covered by n-alkanethiolate self-assembled monolayers (G48). FAD was able to partition into the monolayer, but its electron-transfer rate decreased as film thickness increased, apparently due to increased ET distance. Nakashima et al. incorporated flavin molecules into synthetic lipid bilayers on gold electrodes (G49). In this study,

Analytical Chemistry, Vol. 66, No. 12, June 15, 1994 3B3R

they demonstrated the regulation of flavin ET through control of the thermal phase transition of the bilayer. Mallik and Gani immobilized an isoalloxazine species on a gold electrode and conducted a detailed study of the effect of pH on its surface redox potential and electron-transfer rate constant (G50). pH-dependent conformational changes play a key role in the observed electrochemical properties.

Protein Electrochemistry (emphasizing interfacial electron transfer and biochemical studies). Exciting advances continue to emerge from the protein electrochemistry field, which has experienced a very active two-year period. Whereas simply obtaining a reproducible voltammetric response for small redox proteins remained a challenge some ten to fifteen years ago, that situation has since changed quite decisively. Obtaining voltammograms for cytochromes, ferredoxins, and small blue copper proteins is now a commonplace endeavor. Developing a clear, molecular-level understanding of such “simple” protein/electrode reactions, however, remains a challenge, and indeed, many publications and much controversy have ensued. Other major trends during this time period include the following: direct electronic communication between electrodes and larger enzymes; voltammetry of protein and enzyme monolayers; and the increasing success of protein voltammetry in solving significant biological problems.

“Simple” Electron- Transfer Proteins (Cytochromes, Ferre- doxins, Blue Copper Proteins). Gold electrodes modified with adsorbed “promoters” are widely used in electrochemical investigations of small ET proteins. Several recent papers addressed the mechanism by which such promoters work. Niki’s group described a spectroelectrochemical study of the cytochrome c reaction a t a gold electrode in the presence of the original Eddowes/Hill promoter 4,4’-bipyridyl (G51). They concluded that the interaction of this promoter with cytochrome c is relatively weak and that it acts in the adsorbed state to inhibit the unfolding of coadsorbed cytochrome c as well as to provide a suitable interface. An electrochemical QCM study was reported that provided evidence for weak adsorption of 4,4’-bipyridine on gold electrodes (G52). Cotton and co-workers reported the interesting result that even more weakly adsorbed molecules, namely, 2,2’-bipyridine and pyrazine, could exhibit promoter activity for cytochrome c electrochemistry when appropriate adsorption protocols are followed (G53). These molecules had previously been viewed as nonpromoters.

The most successful gold electrode promoter for cytochrome c electrochemistry is the strongly adsorbing bis(4-pyridyl) disulfide, which was first described by Taniguchi. Ellipso- metric evidence was described supporting the idea that bis- (4-pyridyl) disulfide prevents unfolding of irreversibly adsorbed cytochrome c at the gold surface (G54), and it was furthermore suggested that electron transfer occurs in some manner through an adsorbed monolayer of cytochrome c. In situ STM images of the bis(4-pyridyl) disulfide/gold interface in water suggested ordering of the organic monolayer (G55). In an interesting study from Taniguchi’s group, the effect of chemical modification of surface lysines, Le., conversion to negative charge, was examined (G56). Promoter-modified electrodes turned out to be significantly less adept a t recognizing modified cytochrome c molecules than cytochrome oxidase. Haladjian et al. used modified gold electrodes in the

first reported electrochemical investigation of rusticyanin (Thiobacillus ferrooxidans), a blue copper protein with a molecular weight of ca. 16.5 kDa (G57). An especially intriguing observation was that the direct electrochemistry of this basic protein (IEP = 9.1) was promoted well by bis(4- pyridyl) disulfide but not by several other known promoters of cytochrome c (IEP = 10) electrochemistry. Finally, an examination of the influence of promoter surface coverage on cytochrome c electrochemistry was described by Bond et al. (G58). At submonolayer coverage of bis(4-pyridyl) disulfide, a sigmoidal voltammetric wave shape resulted, which was attributed to radial diffusion a t microscopic reactive sites.

A different approach for promoting the electrochemistry of small proteins involves the use of lipid-modified electrodes. Nakashima et al. reported that cytochrome c undergoes direct electron-transfer reactions a t gold electrodes modified by a Langmuir-Blodgett mercaptophosphatidylcholine monolayer (G59). Tollin and co-workers described a self-assembled lecithin bilayer-modified gold electrode that successfully promoted the direct electrochemistry of thioredoxins (ca. 12 kDa molecular mass) via their disulfide/dithiol redox activity (G60). In previous studies, this particular modified electrode had shown electroactivity for metalloproteins.

Conductive metal oxide electrodes, particularly indium oxide, also continue to be useful for studies with small ET proteins. It was shown definitively that the presence of deamidated or oligomeric forms of cytochrome c interfere with the reaction of this protein a t indium oxide, but much less so a t promoter-modified gold (G61). Daido and Akaike reported a detailed ionic strength and pH study of the reaction of cytochrome c a t indium oxide (G62); their results supported Coulombic interfacial attraction as the dominating factor. Indium oxide electrodes also were shown to give good responses for negatively charged ferredoxins in the presenceof polylysine (G63). Coulombic attraction is also known to be the dominating force in the interaction of cytochrome c with tin oxide electrodes. Using chronoabsorptometry, Collinson and Bowden determined adsorption isotherms for this system as a function of ionic strength, solution composition, and oxidation state (G64). A report of a “solid-state” promoter of cytochrome c, namely, a porous layer of y-alumina on glassy carbon, was presented (G65). These results may have ramifications for those who use alumina polishing media.

Edge-plane pyrolytic graphite (EPG) has been widely used in studies of small negatively charged proteins, typically in the presence of inorganic cationic promoters. Datta et al. proposed that, for ferredoxin reactions at EPG, the promoter induces a weak adsorption of the protein with Frumkin isotherm behavior subsequently resulting from lateral repulsive interactions (G66). EPG direct electrochemistry was used to characterize the thermodynamic and ET kinetic behavior of four plastocyanins (G67), with the finding that the parsley species behaved significantly different from poplar, spinach, and cucumber. Analysis of CV results using a microelectrode, radial mass transfer, model provided support for the view that the EPG surface is electroactively nonuniform toward protein electron transfer.

There were a growing number of significant studies that emphasized the direct electrochemistry of protein solutions as a means to address questions of biochemical importance.


Clearly there is a growing recognition of the potential of this approach for investigating protein energetics and dynamics, duein part to thecontinued maturing of the technique. Indium oxide electrodes were used in a combined electrochemical/ spectroscopic (CD)/calorimetric (DSC) study of cytochromes c from a variety of vertebrate species, as described by Hawkridge and co-workers (G68). Conformational stability of the cytochromes was linked to differences in amino acid sequences and the physiological temperature of the source organism. Barker and Mauk utilized CV in conjunction with edge-plane pyrolytic graphite electrodes to examine the alkaline form of cytochrome c and some variants (G69). They reported the first measurement of the formal potential of the alkaline form of cytochrome c and gave a complete thermodynamic description of the pH-dependent redox cycle involving the native and alkaline forms. McLendon and co-workers measured the formal potential of guanidine hydrochloride- unfolded cytochrome c and determined a 10 kcal/mol difference in stabilization energy between the reduced and oxidized forms of the protein (G70). Independent confirmation of this result was given by Pielak and co-workers (G71) and extended to urea denaturation conditions. Both of these studies made use of the bis(4-pyridyl) disulfide-modified gold electrode. Cysteine-modified gold electrodes were used in the first example of a high-pressure protein electrochemical experiment (G72). A determination of the difference in molar volume between ferri- and ferrocytochrome c confirmed that ferrocytochrome c has a more compact structure. Initial electrochemical reports appeared for the following small electron-transfer proteins: Achromobacter cycloclastes pseudoazurin (G73), a blue copper protein from Alcaligenes faecalis (G74), and cytochrome c‘ from Rhodospirillum rubrum (G75). This latter paper also presented some interesting results bearing on the role of promoters for cytochrome electrode reactions. Reports also continued to appear in which electron-transfer proteins serve the role of mediators for complex enzyme systems, thus allowing bimolecular interactions and catalytic reactions to be investigated in a physiologically relevant manner. Electrochemical studies of this type were conducted on the 66-kDa hexaheme enzyme nitrite reductase from Desulfouibrio desulfuricans (G76), another nitrite reductase from Alcaligenes faecalis (G77), and Desulfouibrio gigas hydrogenase (G78), an 89- kDa molecule containing one nickel and three F e S centers.

Electrochemistry of protein monolayers is a subject that is continuing to generate increasing interest. Although scattered reports can be found in the literature from a decade or more ago, it is only within the last several years that the potential of this approach has become more evident. During the last two-year period, Armstrong’s group continued their work with ferredoxins adsorbed on aminocyclitol-modified pyrolytic graphite electrodes. Their CV study of the kinetics of thiolate ligand binding to the (3Fe-4S) cluster of the protein ferredoxin I11 from Desulfouibrio africanus (G79) is an excellent example of the capability of monolayer electrochemistry for probing the coupling of ligand exchange and electron transfer. Bowden’s group continued their studies of cytochrome monolayers emphasizing elucidation of electron- transfer kinetics and mechanisms. The use of COOH- alkanethiolate self-assembled monolayers (SAMs) as plat-

forms for docking basic cytochromes appears promising. In a CV and impedance study of horse cytochrome c adsorbed on Au/S(CHz)l&OOH, the electron-transfer rate was found to be consistent with predictions from nonadiabatic Marcus theory (G80). Collinson et al. demonstrated the covalent attachment of electroactive cytochrome c to SAM/Au electrodes using carbodiimide coupling in conjunction with electrostatic orientation (G81). In a related study, Cooper et al. described the quasi-reversible voltammetry of cytochrome c covalently attached to the N-acetyl cysteine-modified gold electrode via carbodiimide chemistry (G82). Cytochrome CISAM electrodes were used by Reeves et al. to demonstrate the application of square-wave voltammetry to quasi-reversible surface species (G83). There were a number of other quite interesting cytochrome monolayer studies. Ueyama et al. demonstrated vectorial electron transfer across a flavolipid L-B monolayer-modified electrode to an adsorbed layer of cytochrome c (G84). Cytochrome c was also found to be electroactive when adsorbed to electrodes modified by a composite layer consisting of a triblock polyanion and a cationic lipid (G85). These layers showed a marked pH dependence of the cytochrome response.

Prior spectroscopic and spectroelectrochemical studies have contributed importantly to our understanding of electroactive protein monolayers and it seems a sure bet that this area will continue to intensify. Using SERS, Hobara et al. showed that cytochrome c immobilized by adsorption on the bis(4- pyridyl) disulfide/silver electrode exhibited a native 6cLS configuration and formal potential, in contrast to its behavior at bare silver or bis(Cpyridy1) disulfidelgold electrodes (G86). Visible absorption spectra of ferri- and ferrocytochrome c monolayers on tin oxide electrodes, reported by Collinson and Bowden (G87), also supported a native conformational state for the protein on this electrode material. Mantele and co- workers described FT-IR thin-layer spectroelectrochemical characterizations of cytochromes utilizing unmediated electrochemistry at modified gold minigrid electrodes. This technique, which provides reduced minus oxidized difference spectra, should complement Raman techniques nicely in providing detailed structural information associated with redox changes in metalloproteins in solution. In one of their papers, a detailed characterization of horse cytochrome c redox chemistry in terms of secondary structure as a function of pH, temperature, and electrode promoter was provided (G88). In another paper, detailed structural changes associated with the redox chemistry of tetrahemic cytochromes c3 were described (G89). This technique is well-suited to proteins which can be prepared at reasonably high concentrations, typically millimolar or greater.

Myoglobin and Hemoglobin. The prospects for the direct electrochemistry of these oxygen carriers improved significantly during this time period. Sample purity was previously established as an important element in achieving myoglobin voltammetry at indium oxide electrodes. Tominaga et al. demonstrated quantitatively that surface hydrophilicity of the indium oxide electrode is also a crucial factor in this reaction (G90). They achieved quasi-reversible cyclic voltammetric responses for both sperm whale and horse myoglobin at highly hydrophilic In203 surfaces prepared by extensive detergent sonication. An earlier paper from the same group had

Analytical Chemistty, Vol. 66, No. 12, June 15, 1994 0 395R

described their initial voltammetric results for the horse myoglobin species (G91). The redox energetics, electron- transfer kinetics, and ligand dissociation kinetics of horse metmyoglobin and cyanomyoglobin were explored by Hawkridge and co-workers a t the indium oxide electrode surface (G92) . Only the six-coordinate species Mb(II1)L (L = CN-, HzO) were found to undergo facile electron transfer, with the cyano form exhibiting a considerably enhanced ET rate. Rickard and co-workers described thin-layer spectroelectrochemical measurements of redox potential as function of pH and heterogeneous ET rates for hemoglobinon an indium oxide electrode (G93). Finally, polyethylene oxide-modified myoglobin was found to be stableand electroactive (irreversible ET a t indium oxide) in a PEO oligomer medium (‘394).

Other electrodes besides indium oxide have been developed in past years for use with the globins. Hemoglobin was found to be electroactive at polymerized Azure A film electrodes (G95) and at thionine-modified electrodes (G96). These two electrodes were each capable of driving both the reduction and oxidation directions of the Fe(III)/Fe(II) hemoglobin conversion.

Enzymes: Unmediated Electrochemistry. Achieving electrical communication between redox enzymes and electrodes continues to be one of the most interesting and promising areas of protein electrochemistry. Articles concerned with establishing enzyme/electrode interfacial communication have been selected for this subsection. Those articles focusing more on electrocatalytic aspects can be found under Enzyme Electrodes.

An important activity that continues to flourish is the unmediated electrochemistry of native unmodified redox enzymes, including integral membrane proteins. Complexes originating from the mitochondria of various species were the topic of several accounts. The terminal complex, cytochrome oxidase, was immobilized electroactively into a membrane environment on n-octadecanethiol-modified gold electrodes using a cholate dialysis procedure (G97). Voltammetry consistent with direct electron transfer between the electrode and oxidase was observed, as was the catalytic turnover of solution cytochrome c. Salamon et al. reported that bovine cytochrome oxidase directly transfers electrons when incorporated into lecithin bilayer-modified indium oxide electrodes, the two observed voltammetric processes being assigned to the heme a and CUA centers (G98). Spinach cytochromef. another integral protein, was also found to be electroactive at the same type of electrode. Armstrong and co-workers described the direct electrochemistry of Escherichia coli succinate dehydrogenase (hydrophilic portion of complex 11) immobilized by adsorption on edge-oriented pyrolytic graphite electrodes (G99). Unusual “diode-like’’ behavior was observed under conditions of linear potential scan, as evidenced by the severe retardation of the reverse reaction, fumarate reduction, as the driving force was increased. Using the same monolayer approach, a detailed description of the chemically reversible electrochemistry of E. coli fumarate reductase was also given (GI00) . Redox potentials for the FAD and (4Fe-4s) centers were obtained, and a turnover number of 840 s-l for electrocatalytic fumarate reduction reported from RDE measurements. Other electrochemical experiments with mitochondrial enzymes were published by Monbouquette and

Kinnear. In one study they successfully immobilized electrocatalytically active fumarate reductase in self-assembled monolayers on gold electrodes using a dialysis procedure (GIOI) . Electrochemistry and electrocatalytic functioning of E. coli fumarate reductase in micellar media was also described although the electrode coupling in this case was mediated by decylubiquinone (GI02) .

Additional evidence supporting the existence of direct interfacial electron transfer was provided for a number of other redox enzymes, including the following two reports on hydrogenase. Bianco and Haladjian reported that hydrogenase from Desulfovibrio vulgaris (Hildenborough) transfers electrons directly a t pyrolytic graphite electrodes in the presence of polylysine (G103). At small overpotentials, reversible hydrogen electrode behavior could be observed. Direct electron transfer of hydrogenase (Thiocapsa roseopersicina) was also reported to occur a t cadmium sulfide particles under illumination (G104). The redox properties of human and bovine copper-zinc superoxide dismutase (SOD) species as a function of pH, single site mutations, and inhibitors were characterized by direct electrochemistry a t gold electrodes using 1,2-bis(4-pyridyl)ethene as a promoter (GI05, G106). Shinohara reported the direct electrochemistry of the 40- kDA flavoenzyme sarcosine oxidase a t textured titanium dioxide semiconductor electrodes (GI07).

Efficient enzyme/electrode electron transfer is critically important for the functioning of amperometric biosensors. A survey of publications on “wired”enzymes, enzymes entrapped in electronically conductive materials, and mediated coupling of enzymes for sensors, can be found in the section on Enzyme Electrodes. To conclude the present section, we highlight three reports of unmediated electrochemistry of unmodified enzymes of particular importance to bioanalysis. Zhao et al. reported that when horseradish peroxidase is irreversibly adsorbed on colloidal gold particles, direct electron transfer between the heme and the gold takes place (GI08) . The electronic coupling may be related in some manner to the curvature of the gold substrate; the same behavior was absent for planar electrodes. lkeda et al. described some interesting observations regarding direct electron transfer between dehydrogenases and various electrodes (G109). Alcohol dehydrogenase and D-glUCOnate dehydrogenase from bacterial membranes, upon being irreversibly adsorbed on bare metal or carbon electrodes, showed significant electrocatalytic activity in the absence of mediators. Finally, a promising example that highlights the possibilities for trace voltammetric detection of sulfur-containing proteins was presented. Adenosine deaminase was detected at a reported limit of 2 ppb using adsorptive stripping square-wave voltammetry at mercury electrodes (GI I O ) .

Other Studies ofproteins and Enzymes. A powerful FT- I R thin-layer spectroelectrochemical technique was utilized to provide the first vibrational IR spectra for the primary electron donor of photosynthetic reaction centers from Rhodobacter sphaeroides and Rhodopseudomonas viridis (GI I I ) . Redox-driven difference spectra were generated using direct electrochemistry a t a gold minigrid electrode. In a second study, FT-IR spectroelectrochemistry and photochemistry were employed to provide unprecedented insight into the interactions of the quinone electron acceptors in the


R. sphaeroides reaction center (GI 12). Both mediated and direct electrochemistry were exploited in this study. Stank- ovich and co-workers described a very nice application of mediated EPR spectroelectrochemistry to the redox thermodynamics of electron-transfer flavoprotein-ubiquinone oxi- doreductase (ETF-QO), an iron-sulfur flavoprotein from the inner mitochondrial membrane (GI 13). Three overlapping redox potentials associated with the two redox centers were resolved, making possible the first complete thermodynamic description of electron transport from fatty acid oxidation substrates to the mitochondrial respiratory chain. Mediation was also used in an investigation of Fe(II1) reduction in ferritin performed using thin-layer spectroelectrochemistry (GI 14). An in-depth investigation of mediator/enzyme kinetics was reported by Coury et al. for sulfite oxidase, a molybdoheme, in reactions with several organic mediators (GII5) .

Sagara et al. described an interesting method for the determination of molar absorptivities of electron-transfer proteins using optically transparent thin-layer spectroelectrochemistry (GI 16). This method, which conveniently does not require accurate knowledge of protein concentration, was applied to C-type cytochromes.

A few papers of note also dealt with the interfacial behavior and electrochemistry of proteins not normally the subject of redox electrochemical studies. Randriamahazaka and Nigretto carefully examined the adsorption behavior of thrombin, a protease from the blood-clotting cascade, on carbon paste electrodes for a wide range of experimental conditions (GI 17). Subsequently, a voltammetric assay for thrombin was developed based on the ability of irreversibly adsorbed thrombin to cleave an electroactive label from its substrate (GI 18). Roscoe et al. investigated the irreversible adsorption behavior of a whey protein, @-lactoglobulin, on platinum electrodes as a function of temperature and pH (G119). A SERS examination by Reipa et al. of insulin adsorbed on silver electrodes indicated that binding to the electrode occurred primarily via ionized tyrosine and carboxy terminal ends at potentials positive of the pzc (G120). The adsorption of human serum albumin on tin oxide electrodes was characterized in a careful experiment by Asanov and Larina utilizing total internal reflection fluorescence spectroelectrochemistry (GI 21) .

Photobioelectrochemistry. In addition to some fundamental studies on reaction centers cited in the preceding section, there were some other projects of interest. Katz and co-workers examined chemical aspects of Pt and Pt- amalgamated electrodes in relation to quinone mediation of adsorbed photosynthetic reaction centers (G122, GI23). Photoexcitation of Ti02 particles was used to drive the superoxide dismutase catalytic cycle via photogenerated superoxide (GI24). Finally, soluble mediators were used as electron donors in photoelectrochemical characterization of pigments in thylakoid membrane fractions (GI25).

The design and development of amperometric biosensors in which enzyme reactions are coupled to amperometric or voltammetric electrodes was the single largest subject area reviewed in terms of number of papers considered. Papers selected for citation in the present document generally displayed either an emphasis on fundamental scientific advancement or an emphasis on the dem-

Enzyme Electrodes.

onstration and characterization of new materials, concepts, or strategies. The reader should note that Janata’s chapter on sensors in this same issue (GI26) includes comprehensive coverage of amperometric biosensors. Furthermore, in odd years, amperometric biosensors are included in the Application Reviews issue, most recently by Wang in the Clinical Chemistry chapter (GI27).

Glucose sensors based on the glucose oxidase catalytic cycle continued to dominate the amperometric biosensor field over the last two years. The availability and stability of this enzyme, as well as its obvious application in the monitoring of diabetes, have been key factors in its popularity. An informative review article on glucose oxidase was cited earlier (G15). A new development that is sure to have major impact on the glucose sensor field is the recently reported crystal structure of partially deglycosylated glucose oxidase from Aspergillus niger at 2.3-A resolution (GI28). One other comment of general interest is the oft-discussed application of glucose sensors for in vivo monitoring. Although impressive advances have been made in the development of glucose sensing devices, a number of imposing problems stand in the way of their implementation as long-term implantable devices, as succinctdy reviewed by Reach and Wilson (GI 29).

Theory. Albery and co-workers continued their analysis of steady-state amperometric biosensor behavior with contributions concerning enzyme/electrode coupling via homogeneous solution mediators (GI30), which is of relevance to the mechanism of conducting organic salt electrodes, and also multienzyme sensors (G131). The mechanisms attendant to the functioning of organic salt enzyme electrodes were also addressed from a different viewpoint (GI32).

Two theoretical sensor studies in which the enzyme catalysts are incorporated into polymer films were given. In one, the steady-state response of glucose oxidase/poly(pyrrole)- (PPy-) based sensors was extended to include the case where a PPy- oxidizable mediator (benzoquinone) was present in the film (GI33). In the other, steady-state and transient responses were provided for mediated enzyme electrocatalysis within both electronically conductive and insulating polymer films (GI 34).

Finite-volume modeling was applied to evaluate the transient response behavior of various electrode configurations, including the case of a free enzyme layer confined by a semipermeable membrane and for enzyme immobilized on either size of a polymer membrane adjacent to the electrode (GI35). Explicit-point modeling of transient and steady-state responses was performed for the case of fully soluble enzyme (glucose oxidase), substrate (glucose), and mediator (GI36). Digital simulation was also used to model the case of submonolayer coverage of an enzyme whose interaction with its substrate releases a redox label that can be detected electrochemically (GI 37). The intended applications are in assaying proteases in turbid samples and for characterizing certain components from the blood coagulation system.

Pardue and co-workers presented two alternative measurement schemes to the usual nonequilibrium steady-state current measurements. Utilizing a thin-layer cell configuration, complete reaction of substrate in a small fixed volume gives rise to equilibrium-based measurements of concentration (GI 38), which can extend the linear dynamic range and reduce


dependence on certain experimental variables. In another study, transient currents measured a t short times were used with appropriate theoretical models that predict the steady- state currents that would result at longer times (G139). Glucose oxidase entrapped within an osmium-based redox polymer film on a glassy carbon electrode was employed as the experimental system in these two studies.

Lyons et al. described a theoretical model for a heterogeneous thin-film sensor in which Michaelis-Menten kinetics apply to substrate/product conversion a t dispersed catalytic particles within a Nafion film (C140). Although the system examined was dopamine oxidation, the theory also has relevance to enzyme electrodes.

Tatsuma and Watanabe reported theoretical descriptions for the case of monolayer and bilayer enzyme electrodes in which a soluble mediator is responsible for enzyme/electrode communication. Both transient (G141) and steady-state (G142) responses were described and compared with results using glucose oxidase sensors.

Redox “Wired” Enzymes. Some important developments were reported that bear upon the mechanism of electron transfer to the FAD sites in glucose oxidase. Mikkelsen, English, and co-workers provided an insightful characterization of ferrocene-modified glucose oxidase molecules (GI 4 3 ) . They concluded that the location of lysine modification sites results in long-range ferrocene-to-flavin intramolecular electron transfer as the rate-limiting factor in electrochemical conversion. This view is supported by the available crystal structure for the enzyme (G128). Another pertinent paper of fundamental interest, although not dealing specifically with “wiring”, is the detailed voltammetric study reported for the glucose/ glucose oxidase reaction mediated by one-electron reagents (G144). Apparently the mediator forms a precursor complex with glucose oxidase in a site near the flavin. Interesting experimental measurements of mediator complexation with glucose oxidase were reported for hydroquinonesulfonate (G14.5, G146).

Polymer Film Electrodes. Since Degani and Heller’s seminal papers on ferrocene-modified glucose oxidase in the 1980s, the redox “wiring” approach to coupling enzymes and electrodes has flourished, especially as regards entrapment of the enzyme within redox polymer films. Heller’s review is a good introduction to this area (G13). It is now possible to prepare three-dimensionally stable polymer films that provide a friendly hydrogel microenvironment for enzymes as well as good electrical communication with the substrate electrode. Aoki and Heller reported fundamental measurements of electron-transfer diffusion coefficients for osmium( II/III)/ poly(viny1pyridine) (Os-PVP) hydrogel films as a function of thedegree of diepoxide cross-linking (G147). “Redoxepoxies” of the Os-PVP type have been quite successful for entrapping redox enzymes in the construction of reagentless biosensors. Heller’s group reported several examples including horseradish peroxidase sensors for hydrogen peroxide and NAD(P)H detection (G148), oxidase sensors for detection of L-cu- glycerophosphate and L-lactate (G149), and a glucose dehydrogenase sensor for glucose detection (GI 50). Bienzyme sensors based on Os-PVP polymers were also described by the same group (G151) as well as by Michael and co-workers (G152) . In these devices, Os-PVP-wired horseradish per-

oxidase is oxidized by the hydrogen peroxide generated by the reaction of a second enzyme with the substrate. This strategy can be used with difficult-to-“wire” enzymes such as choline oxidase for detection of choline. Evidence supporting the feasibility of a trienzyme sensor incorporating acetylcholinesterase was also reported (G152). Michael’s group also demonstrated that Os-PVP/peroxidase sensors could be used to detect H202 in CO2-based fluid near its critical point, the first example of its type (G153).

Glucose oxidase sensors based on entrapment within other redox polymers was also reported. Ferrocene-based polymers for this purpose were described by several groups. These included ferrocene-substituted polylysines (GI 5 4 , polymers based on ferrocenylenemethylene structure (GI 5 3 , ferro- cenylsiloxane-ethylene oxide copolymers (GI 56), ferrocenyl- acrylamide-acrylic acid copolymers (G157), and commercially availablepoly(viny1ferrocene) (G158). The latter two papers also discussed theoretical considerations regarding steady- state sensor response. Other reported redox polymers that were successfully used to wire glucose oxidase included a tetrathiafulvalene-substituted siloxane polymer (G159) and polymercapto-p-benzoquinone (GI 60).

The second major focus in developing polymeric enzyme sensors has been the entrapment of enzymes within polypyrrole and other conducting polymers, which was first described by Foulds and Lowe in the 1980s. An advantage of this approach is the ability to prepare the polymer/enzyme film by a one- step electropolymerization, which is attractive from a com- mercialization perspective. The functioning of conventional polypyrrole-type enzyme electrodes is not as straightforward as for the redox polymer film electrodes. Typically, the PPy matrix appears to function primarily as a three-dimensional support for the enzyme with electrochemical communication occuring via internal redox of a mediator (e.g., oxidation of H102) or cosubstrate species. During this two-year time period, polypyrrole was clearly the material of choice for most researchers, usually in combination with glucose oxidase, which generates H202 that is oxidized at the substrate electrode. Rotating ring disk studies by BClanger et al. examined, among other factors, the effect of PPy film thickness and glucose concentration (G161). The catalytic reaction was found to mainly occur a t the PPy/solution interface except a t high glucose concentration. In an interesting study, Cooper and Bloor coimmobilized catalase with both glucose oxidase and glucose apooxidase to investigate the mechanism of the PPy biosensor (GI 62). They concluded that electron transfer between PPy and entrapped enzyme is very inefficient. Significant rates of electron transfer were noted, however, when a small electron-transfer protein, cytochrome c, was entrapped within PPy (G163), In other studies, Tatsuma et al. prepared horseradish peroxidase/PPy electrodes (G164) and bienzyme PPy electrodes that contained both peroxidase and glucose oxidase (G165). A role for the PPy in enhancing electrochemical communication between the electrode and enzymes was proposed.

Coentrapment of electron-transfer mediators along with enzymes in conducting polymers was described by several groups. In the case of glucose oxidase amperometric sensors, the rationale for using a mediator is avoidance of the HzOz product. The high potentials needed to oxidize H201 are


sufficient also tooxidize key interferents, e.g., ascorbate, urate, glutathione, etc. Operation at lower potentials is clearly desirable. Some concern has also been raised that H202 can irreversibly oxidize PPy in an uncontrolled fashion, which may be a further unwanted side effect. When mediators are employed, however, their downside is leachability, which must be controlled adequately in order to fabricate practical devices. Bartlett et al. demonstrated that coimmobilized ferricyanide can mediate the glucose oxidase reaction while entrapped within the PPy film (GI66) . Yoneyama and co-workers coimmobilized 8-naphthoquinonesulfonate, NAD, and glucose dehydrogenase into PPy using a single-step process to produce a mediated PPy sensor for glucose (GI67) . Also using a one- step deposition process, Aizawa and co-workers prepared a PPy/fructose dehydrogenase sensor for detecting fructose that incorporated either ferricyanide or a ferrocene derivative as mediator (GI68) . Thesamegroup also described a composite film sensor for fructose detection that was comprised of PPy, TTF/TCNQ, and fructose dehydrogenase (GI69) . The stability of this sensor was found to be superior to a TTF/ TCNQ/fructose dehydrogenase sensor. Using another strategy, Sun and Tachikawa created a glucose sensor in which a PPy/glucose oxidase film was deposited over polymetallo- phthalocyanine (PMePc) films (GI 70) . Oxidation of H202 occurred at a 0.7-V lower potential, apparently due to catalysis at the PMePc/PPy interface.

The reaction mechanisms for polypyrrole amperometric sensors, including solution mediator reactions, were examined using cyclic voltammetry, impedance spectroscopy, and rotating disk voltammetry by Lyons et al. (GI71) . Cases were considered for mediator reaction only at the PPy surface as well as partitioning into the film. This particular study did not address enzyme issues in particular. One other related report examined the reaction of the benzoquinone mediator at polyaniline films used in biosensor applications (GI 72) .

In other applications involving enzymes entrapped within PPy, the possibility of controlling the activity of the entrapped enzyme via anion doping/undoping was demonstrated using phosphate and pyruvate oxidase (GI73) . Sadik and Wallace reported that the utility of PPy/antibody sensors for human serum albumin was significantly improved using pulsed amperometric detection (GI 74 ) . The mechanism for signal generation is not, however, clear.

Several papers addressed the issue of electropolymerization procedure with the objective of improving enzyme activity and stability. Lowe and co-workers obtained significant improvement on both counts by covalently copolymerizing glucose oxidase into a PPy film via pyrrole-derivatized surface residues (GI 75) . In a following study, the method of pyrrole attachment to glucose oxidase was evaluated, and the kinetic properties of the modified enzyme were measured (GI76) . Cosnier and Innocent described the clever use of a pyrrole- substituted cationic surfactant as the monomer for forming a PPy/tyrosinase electrode for detection of phenols (GI77) . A film of the cationic monomer and the anionic enzyme (IEP = 4.7) was first deposited on a glassy carbon electrode after which electropolymerization was conducted in LiC104 electrolyte. The generality of this particular approach was addressed in additional studies with glucose oxidase and choline oxidase (GI 78 ) . One other nonconventional approach to

forming bioconductive polymers is to use the enzyme as the polymerization initiator. Under mild conditions, it has been shown that bilirubin oxidase initiates polymerization and retains activity in the resultant film of poly( 1,5-dihydroxy- naphthalene) (GI 79) .

The possibility of establishing direct electronic communication between PPy and enzyme monolayers was addressed in the following two papers. An amperometric response for glucose was obtained with glucose oxidase adsorbed on the surface of PPy, which partially filled the pores of an electrode-supported filtration membrane (GI80). Identical responses were obtained under 0 2 or argon with no mediators present. A different approach was taken in the development of a fructose sensor, where a monolayer of fructose dehydrogenase was first adsorbed on Pt, followed by encase- ment in electropolymerized PPy to a thickness of roughly 50-80 A (GI8I) . Evidently the PPy was able to convey electrons between the electrode and the prosthetic group of the enzyme, pyrroloquinoline quinone (PQQ).

There are promising new examples of enzyme “switches” based upon the conductivity properties of conductive polymer films. In these devices, the redox and chemical state of the polymer thin film, and hence its conductivity, are controlled by the reaction products of enzymes, typically immobilized in an adjacent overlayer. Acidification increases the conductivity of polypyrrole. A sensor,for penicillin was described in which the conductivity of a PPy film responded reversibly to pH changes produced by the action of a penicillinase overlayer (GI82) . Conductivity control by pH was also the basis for a glucose sensor based on polyaniline (GI83) . In this paper, the conductivity of a polyaniline film appears to be controlled by pH changes produced by the production of gluconic acid in a glucose oxidase/polyaniline overlayer. A new redox-dependent polyaniline film switch for glucose was developed (GI84), which appears to have faster response time than the original PPy switch. Here, the generation of reduced mediator (TTF) by the action of glucose oxidase results in reduction of the polyaniline film to its insulating state.

The issue of selectivity is of course critically important for developing sensors well-suited for measurements on physiological samples. As mentioned earlier in the discussion on mediated PPy amperometric glucose sensors, the electrooxidation of interferents such as ascorbate, urate, acetaminophen, glutathione, and other species must be adequately minimized. Several interesting approaches based on electrically insulating polymer films have been reported. Maidan and Heller crafted a multilayer electrode consisting of an Os-PVP “wired” glucose oxidase layer on glassy carbon, with an overlayer of horseradish peroxidase for catalytic preoxidation of interferents by H202 (GI 85) . This approach provides impressive performance but does require a constant source of H202, which can be added externally or generated internally via an additional enzyme system. Christie et al. examined plasticized poly(viny1 chloride) as conventional permselective membranes for use with various amperometric biosensors and found this material to be markedly superior to cellulosic membranes for exclusion ofionicinterferentssuchas ascorbateandurate (Gl86).Some progress in reducing the ascorbate interference for H202- detecting glucose electrodes was described by Lowry and ONeill in work on Nafion-covered TTF/TCNQ-based sensors


(G187). One simple yet effective approach involved the addition of stearic acid, which is known to increase the overpotential for oxidations of anions.

A different but more difficult solution to the interference problem is to build permselectivity directly into the enzyme- containing polymer film. In this regard, Centonze et al. obtained good results with a strategy based on conventional electrooxidation of H202 but with a nonconducting over- oxidized PPy/glucose oxidase electrode (GZ88). The one- step procedure resulted in a permselective film that worked well in rejecting some common interferents. Disagreement arose over the mechanism of ascorbate interference in H202- detecting glucose sensors with glucose oxidase entrapped within permselective poly(o-phenylenediamine) films. Lowry and O’Neill contend that, in addition to primary interference due to ascorbate electrooxidation a t the substrate electrode, oxidation of ascorbate can also occur in a homogeneous reaction with H202 generated in the sensor (G189). On the other hand, Palmisano and Zambonin ascribe “nonprimary” interference to structural changes in the sensor arising directly from ascorbate electrooxidation, Le., electrode fouling (GI 90). Electrochemically deposited poly(pheny1ene oxide) film electrodes may also prove to be useful as enzyme-entrapping permselective layers (G191). An initial study of this type of material with entrapped glucose oxidase examined the influence of the phenol monomer on the resulting sensor performance but did not report on interferences (G192). Initial evaluations of the permselective capability of Nafion when glucose oxidase was directly incorporated were not very promising (G193, G194).

The discovery during the mid- 1980s that many enzymes can function catalytically in organic media had led to the development of organic-phase amperometric biosensors. Adsorption has been a favored mode of immobilization due to insolubility of the enzymes. Wang and co-workers have demonstrated the advantages of enzyme entrapment within an Eastman AQ poly(ester-sulfonic acid) polymer phase for horseradish peroxidase and tyrosinase (G195) and for laccase (GI 96).

Monolayer- Type Electrodes. Included in this subsection are studies on enzyme electrocatalysis and amperometric biosensors in which enzymes are immobilized in monolayer or submonolayer configurations. Related monolayer enzyme electrochemistry citations can be found under Enzymes: Unmediated Electrochemistry. Sensor configurations of the enzyme monolayer type have potential advantages, e.g., rapid response times, as well as drawbacks, e.g., restricted dynamic range.

Direct electron transfer between enzymes and conductive substrates, if efficient, would of course be a highly desirable basis for fabricating monolayer biosensors because exogenous mediators would not be required. The peroxidases have been the most highly studied enzymes in this regard, and interest continued unabated during this two-year period. Using rotating disk voltammetry, Scott et al. characterized the electrocatalytic functioning of baker’s yeast cytochrome c peroxidase (CCP) that had been irreversibly adsorbed on edge- oriented pyrolyticgraphite electrodes (G197). Adsorbed CCP appears to function similarly to solution CCP with regard to its reactions with H202 and known inhibitors. Using

voltammetry and ellipsometry, Armstrong et al. investigated the mechanism for CCP adsorption onto edge-oriented pyrolytic graphite electrodes in the presence of neomycin (G198). Evidence supported a heterogeneous adsorption model a t submonolayer enzyme coverage involving localized electrocatalytic sites that behaved voltammetrically as microelectrodes. Gorton’s group has played a very active role in the area of mediatorless peroxidase biosensor development, and some of their prior and recent results along with a historical summary can be found in ref G12. This is an excellent article for researchers who wish to get up to speed in this particular area (as of 1992). With an eye toward immunoassay applications, Ho et al. fabricated mediatorless peroxide sensors based on direct electron transfer between adsorbed horseradish peroxidase (HRP) and activated carbon or platinized activated carbon electrodes (G199). Kulys et al. reported that the electroenzymatic reduction of H202 at mediatorless carbodiimide-immobilized HRP graphitic electrodes was activated by various organic hydride donors (G200), which might indicate that not all adsorbed peroxidase molecules were electroactive.

Having previously shown that electrocatalytically active heme nonapeptide could be covalently attached to tin oxide electrodes, Tatsuma and Watanabe characterized its ability to function as an interference-typesensor for various imidazoles (G201). Coordination of imidazole ligands to the ferric iron blocks the catalytic current associated with H202 reduction.

Evidence for direct electrical communication was provided by Ikeda and co-workers for two enzymes of analytical importance, diaphorase (Bacillus stearothermophilus) and ferredoxin-NADP+ reductase (G202). On carbonaceous electrodes, unmediated catalytic currents were detected in the presence of substrate.

A number of papers dealt with the issue of covalent immobilization strategy. Carbodiimide coupling has proven its worth in many applications, both bioelectrochemical and otherwise. To this end, a useful and general modification of carbon surfaces by electroreduction of substituted aromatic diazonium salts has been applied to the immobilization of glucose oxidase on glassy carbon (G203). 4-Phenylacetic acid groups attached to the GC surface can serve as sites for subsequent carbodiimide coupling of enzymes. Willner et al. covalently attached glutathione reductase to gold electrodes via a chemisorbed cysteic acid active ester reagent (G204). In situ redox “wiring” of the enzyme with bipyridinium relays was subsequently achieved using carbodiimide coupling chemistry. The same group described an alternative means for achieving covalent attachment to gold via an isothiocyanate reagent, trans-stilbene-( 4,4’-diisothiocyanate)-2,2’-disulfonic acid, bonded to chemisorbed cystamine (G20.5). Streptavidin- biotin coupling is another very useful bonding technology. Quite reasonable selectivity was achieved in a glucose sensor in which streptavidin-glucose oxidase was attached to a biotinylated self-assembled phospholipid bilayer (G206). Several other covalent enzyme immobilization schemes that might prove useful were noted by your reviewer (G207-GZ09) although the studies cited were nonelectrochemical in nature. The work being carried out by Whitesides’ group regarding protein adsorption on self-assembled monolayers (G210) may also be of relevance to monolayer enzyme electrode designers.


The immobilization and electrocatalytic behavior of Desulfovibria gigas hydrogenase on amphiphilic bilayers was described by Parapleix et al. (G211). Immobilization was largely driven by hydrophobic interactions, and the mediated electrocatalysis involved two-dimensional diffusion of octa- decylviologen species in the pores of aluminum oxide films on gold.

Finally, the fabrication and performance of light-activated glucose sensors based on n-type silicon substrates were described by Dicks et al. (G212). An enzymelmediator monolayer configuration was achieved by adsorbing glucose oxidase onto a ferrocene-derivatized polypyrrole layer that had been electropolymerized on n-Si.

Carbon Paste and Other Bulk Composite Electrodes. A new trend in biosensors that has emerged in recent years is the incorporation of enzyme (and mediator, if required) directly into carbon paste and other bulk carbon composite materials. Among the potential advantages of these reagentless bioelectrodes are ease of fabrication, electrode stability, and surface renewal by simple abrasion or other mechanical means. Wang’s group described a number of developments in this area including the incorporation of horseradish peroxidase into carbon paste and graphite/epoxy for the detection of organic peroxides (G213). No mediators were required as the H R P was able to communicate directly with the carbon particles. The graphite/epoxy vehicle was also successfully used with dehydrogenase enzymes, in particular alcohol dehydrogenase, by incorporating NAD+ in addition to the enzyme (G214). A reagentless carbon paste alcohol sensor was designed along these same lines but with the additional inclusion of ruthenium catalyst for lowering the overpotential for NADH oxidation (G215). Enzyme- incorporated graphite/Teflon bulk composite sensors were also described (G216).

Incorporation of additional catalysts in enzymatic carbon paste electrodes was also accomplished by Mizutani et al. (G21 7). They observed significantly lowered overpotentials for H202 oxidation in glucose sensors when either platinum black or cobalt phthalocyanine was dispersed in the matrix.

Kulys and co-workers described their results with several enzymatic carbon paste amperometric sensors that utilized incorporated mediators. Methylene green was used as the mediator in a pyruvate sensor based on entrapped pyruvate oxidase (G218) and an L-lactate sensor based on entrapped L-lactate oxidase (G219). A carbon paste/diaphorase/ mediator composite was investigated for the electrocatalytic oxidation of NADH; Meldola blue proved to be a superior mediator to methylene green in this system (G220). A whole- cell carbon paste electrode for L-lactate was fabricated by incorporation of the yeast Hansenula anomala along with mediators (G221). Cytochrome b~ was suggested as the biocatalytically involved site in the yeast.

Smit and Rechnitz described an interesting Mn2+ sensor in which horseradish peroxidase and a mediator, 1,2-naptho- quinone, were directly incorporated into a carbon paste medium (G222). The presence of manganese ion stimulates the mediated enzymatic reduction of 0 2 , resulting in a current increase. A detailed voltammetric investigation was reported for a carbon paste glucose sensor utilizing glucose oxidase and dimethylferrocene as mediator (G223). Control of the

catalytic rate was shown to be highly dependent on the amount of incorporated mediator. A novel composite glucose sensor was designed by incorporating glucose oxidase along with a mediator, cobalt phthalocyanine, into a colloidal emulsion of graphitic particles (G224). Formation of the biocatalytic layer is accomplished by simple evaporative deposition of the emulsion on a glassy carbon substrate.

Microenzyme Electrodes. Tissue and other in vivo applications along with detection in microenvironments constitute two of the main goals that are driving efforts to miniaturize enzyme electrodes. In addition, miniaturization also holds open the potential for faster responding sensors as well as their eventual incorporation into integrated microelectronic devices. Papers selected for this section displayed an obvious “micro” theme, although in most case! the reader will note that there is considerable topical overlap with one or more other sections. Pantano and Kuhr described the construction and performance of monolayer dehydrogenase sensors based on 10-pm carbon fibers (G225). Enzymes were covalently attached to the carbon surface via avidin-biotin chemistry, and the amperometric signals arose from electrooxidation of enzyme-generated NADH. An extremely fast glutamate sensor based on this strategy exhibited a response time of 300 ms, one of the fastest known. Carbon fibers were also evaluated by Csoregi et al. for constructing mediatorless peroxide sensors based on apparent direct electron transfer with immobilized horseradish peroxidase (G226). Carbodiimide attachment of HRP to heat-treated graphite fibers resulted in the best performance. Carbon fiber disk electrodes, 7 pm, coated with a cross-linked layer of alkaline phosphatase displayed very good performance in thedetection of 4-aminophenyl phosphate (G227). One other carbon fiber-based device, although technically not a microsensor, is the redox-“wired” lactate probe described by Wang and Heller (G228). The unique design feature of this miniprobe is its mechanical flexibility, conferred by bundling together several hundred 7-pm carbon fibers. Microenzymatic sensors were also reported in which carbon fibers were used primarily as conductive supports. Wightman and co-workers described TTF/TCNQ-type enzyme biosensors for glucose and acetylcholine based on capillary-encased recessed-tip 7-pm carbon fibers (G229). With outside diameters on the order of 20 pm, these electrodes are well-suited for in vivo tissue applications. Wang and Angnes reported that a one-step electrostatic codeposition of rhodium and glucose oxidase on carbon fibers results in glucose microelectrodes that exhibit a significantly lessened overpotential for HzOz electrooxidation (G230). Finally, carbon films were employed to make nanoband enzyme electrodes of 35-50 nm thickness by enzyme entrapment within a poly- (0-phenylenediamine) overlayer (G231).

Another popular electrode material for microenzymatic sensors is platinum. Karube and co-workers fabricated cylindrical-geometry glucose sensors from 2-hm Pt fibers by entrapping enzymes in photo-cross-linkable polymer layers (G232). The responses were of the mediated-type, and various experimental parameters were evaluated. Abe et al. constructed implantable glucose sensors from platinized-carbon ring electrodes with a cross-linked glucose oxidase catalytic overlayer (G233). Response times as low as 270 ms were reported, and interference by oxygen was investigated.

Analytical Chemlstry, Vol. 66, No. 12, June 15, 1994 401R

Other platinum-based microelectrodes included those for cholesterol and cholesterol ester, in which enzymes were adsorbed on a porous carbon composite supported on a recessed-tip 50-km Pt wire (G234), and a glucose sensor utilizing monolayer glucose oxidase immobilized in a poly- (phenol) film on 25-pm Pt wires disk electrodes (G235).

Other Enzyme Electrode Studies. For convenience, a number of other significant reports concerning various aspects of amperometric biosensors are collected together here. For the many workers developing biosensors based on the elec- trooxidative detection of HzOz, the paper by Zhang and Wilson describing detailed studies of this reaction a t Pt and Pt/Ir electrodes should be important (G236). The reaction at neutral pH is not fully understood; the studies reported here concentrate on physiological buffer conditions pertinent to biosensor operation. Experimental variables (pH, temperature, electrode conditioning) were found to exert a strong effect on the reaction, and the use of a protective cellulose acetate membrane was found to be advantageous.

A significant contribution to the understanding of organic conducting salt electrodes was due to Lennox and co-workers (G237) in a detailed electrochemical study of TTF/TCNQ and hexamethylenetetratellurofulvalene (HMTTeF)/TCNQ. Both silicone oil and polystyrene binders were used. Their results support the homogeneous mediation mechanism for the electrooxidation of ascorbate, NADH, and reduced glucose oxidase. An evaluation of background currents gave evidence for the view that these salts undergo dissolution even at potentials at which they are normally considered to be stable. Wilde et al. described results of a CV investigation of charge accumulation a t TTF/TCNQ electrodes operating in glucose oxidase biosensors (G238), a phenomenon apparently due to the surface accumulation of a reduced species as a result of glucose oxidation. Xanthine sensors based on the immobilization of xanthine oxidase on TTF/TCNQ/silicone oil substrates were reported by Korell and Spichiger (G239). Exploiting hydrophobic interactions during immobilization resulted in the best performance. Sim analyzed the steady- state kinetic behavior of an ethanol sensor based on the confinement of alcohol dehydrogenase between a membrane and an N-methylphenazinium (NMP)/TCNQ electrode (G240).

Several additional studies were reported that focused on mediator development. In a detailed study, Fraser et al. examined a series of mediators comprised of tris(4,4’- substituted-2,2’-bipyridine) complexes of Fe(II), Ru(II), and Os(II), as electron acceptors for glucose oxidase (G241). It was concluded that the overall charge on the mediator was critical, with + 5 providing optimum electron-transfer kinetics, apparently due to interaction with the anionic active site of the enzyme. Effective heterogeneous mediation of tyrosinase and cytochrome c was achieved through the incorporation of a tetradentate Cu(II)/Cu(I) complex in a Nafion overlayer on glassy carbon (G242). Other mediators reported during this time period included nickelocene, which operates at a lower potential than ferrocene for glucose sensors (G243), the water solubilization of T T F by complexation with 2- hydroxypropyl-0-cyclodextrin (G244), and a dimethyl(meth- y1thio)-substituted tetrathiafulvalene (MTTTF) for use in glucose sensors (G245).

Can electrodes communicate with intact livingcells? Using mediators, the answer is “yes”, as has been demonstrated periodically in the past. The ability to establish lines of electroenzymatic communication between electrodes and whole cells suggests new approaches for enzyme biosensors as well as for microbiological research. Along these lines, Ikeda et al. have reported mediated bioelectrocatalytic reactions of Gluconobacter industrious immobilized on carbon paste electrodes (G246, (3247). In the presence of ferricyanide as mediator, both glycerol and fructose were oxidized at high rates, apparently by dehydrogenases in the cell membranes (G246), and in the presence of p-benzoquinone as mediator, the oxidation of glucose proceeded (G247). Earlier, an example of a bulk yeast carbon paste electrode due to Kulys was cited (G221).

A novel photoelectrochemical device was developed and characterized by Cohen and Weber for potential applications in automated immunoassay and biosensors (G248). Using an optical fiber, the device is able, via an Oz/R~(bpy)3~+/ light reaction, to generate H202, which can then be detected amperometrically a t a gold ring electrode. In their paper, the device was used as a sensor to detect catalase a t subnanomolar concent ration.

Martin and co-workers reported a self-contained sensor concept in which the internal solution components and electrodes are confined to one side of an ultrathin film composite membrane (G249). The glucose/glucose oxidase system was used as a test system.

The concept of using bilayer lipid membrane properties in combination with enzymatic reactions as a basis for chemical sensing was described by Nikolelis et al. (G250). The presence of acetylcholine resulted in small transient currents across BLMs incorporating acetylcholinesterase. The signal arises from a change in double-layer properties attributed to generation of hydrogen ion by the enzymatic reaction.

The entrapment of active glucose oxidase in sol/gel matrices was reported by Audebert et al. (G251). Voltammetric monitoring in the presence of ferrocene mediator and glucose was used to evaluate the activity of enzyme. Ellerby et al. described the entrapment of functional proteins (cytochrome c, superoxide dismutase, myoglobin) in porous, optically transparent, sol/gel matrices (G252). Although not an electrochemical study, this study could suggest possibilities for the design of electroenzymatic experiments and sensors.

Palecek and colleagues, to whom we owe much of our knowledge of polynucleotide interactions at electrode surfaces, discussed the voltammetry of various types of DNA a t HMDE and carbon electrodes (G253, G254). By exploiting the strong affinity of DNA for these surfaces, the analysis of nanogram or lower quantities in sample sizes of 5 L becomes possible using adsorptive transfer stripping voltammetry methods. Characterization by this method of various forms of DNA, i.e., calf thymus, plasmid, single-strand vs double-strand, denatured, and supercoiled, is described in these two papers. Supercoiled DNA was found to resist denaturation on the mercury surface in the potential range of -0.1 to -1.5 V vs SCE (G254).

Covalent immobilization of polynucleotides on electrodes was also reported. Maeda et al. affixed disulfide-modified

Polynucleotides and Nucleic Acids.


calf thymus DNA to gold electrodes by chemisorption (G255), which inhibited the CV response for a ferri-/ferrocyanide solution. The inhibition, however, was found to be reversibly modulated in a concentration-dependent manner by the addition of quinacrine, a cationic drug that binds to DNA, thereby reducing its negative charge. Carbodiimide coupling was employed by Millan et al. to covalently attached a synthetic double strand of DNA, poly(dG)poly(dC), and also denatured calf thymus DNA, to glassy carbon electrodes (G256). The presence of surface DNA was subsequently detected by voltammetry of preconcentrated Co(bpy)j3+, a redox probe that binds strongly to the surface-bound DNA.

The investigation of DNA and its binding with small molecules is another profitable area in bioelectrochemistry. Rodriguez and Bard continued their work with a study of the binding of calf thymus DNA by a complex formed from Mn(II1) porphyrin (MnP) and distamycin A (Dis), an oligopeptide antibiotic and biological inhibitor (G257). Both compounds are known individually as binders of DNA, but only the Mn(II1) species is electroactive. A stoichiometry of MnP(Dis)z was found for the complex.

Thorp’s group continued their efforts on electrocatalytic cleavage of DNA by transition metal complexes. A detailed study of the binding and catalytic behavior of Ru1I(tpy)(bpy)Z-

toward calf thymus DNA was reported (G258). The active cleavage form of this compound is the two-electron RutV electrooxidation product. A similarly functioning species but with increased binding affinity for DNA was obtained by replacing the two bipyridine ligands with a single planar dipyridophenazine ligand (G259). Crystallography of this compound indicated the presence of significant *-stacking interactions that help to explain its higher affinity for DNA.

In Vivo and Cellular Electrochemistry. Central to progress in these areas is, of course, the ability to fabricate ultra- miniaturized electrodes with adequate performance characteristics. The interested reader should also consult the section on Microenzyme Electrodes, which spedfically addresses ultramicroenzyme electrodes. In vivo electrochemistry, especially in the area of neurochemistry, has continued to grow in popularity, and the literature has become quite extensive. Here we note only a limited number of papers of analytical or general interest. Adams’ group described real- time monitoring of electrically stimulated norepinephrine (NA) release in the rat thalamus in the presence of 3,4- dihydroxyphenylacetic acid (DOPAC) (G260, G261). The electrooxidation of these neurotransmitters was followed by fast chronoamperometry at Nafion-coated carbon fibers. Separation of the N A faradaic signal from that due to DOPAC was achieved by differentially controlling the electrode kinetics of the two species by electrochemical pretreatment procedures. Young and Michael reported that electrochemically stimulated dopamine release in the rat striatum could be followed in real-time by fast-scan CV with 500-ms resolution with respect to individual stimulation trains (G262). A critical review and discussion of sensor/tissue interactions associated with in vivo use of carbon paste electrodes in the brain was provided by O’Neill (G263). A careful analysis of signal-to-noise issues attendant to trace analysis of dopamine in the rat brain by fast-scan CV was presented by Wightman and co-workers (G264). In vivo detection of 100 nM dopamine a t S / N of 25

was achieved. A new method for in vivo voltammetric monitoring in the rat brain using a “dialysis electrode” was described by Albery et al. (G265). This device, which utilizes an internal electrode to monitor substances crossing the dialysis membrane, was able to detect glutamate in real time. For in vivo monitoring in subcutaneous tissue, needle-type enzyme sensors for lactate (G266) and glucose (G267) were designed by Wilson’sgroup with careful attention to oxygen interference effects.

Cellular electrochemistry includes voltammetric measurements made either inside (intracellular) or outside (extracellular) single living cells. These types of measurements became feasible during the mid-1980s. Ewing’s group was very active in the area of intracellular electrochemistry, reporting voltammetric measurements made in the giant dopamine neuron of the pond snail Planorbis corneus (G268, G269). In one study, platinized carbon ring electrodes of 2-10-pm diameter were used to monitor intracellular oxygen levels, which were shown to vary with oxygen levels in the bathing solution (G268). The same type of electrode was also used to monitor internal dopamine levels while varying the dopamine concentration in the bathing medium (G269). Active membrane transport of dopamine was suggested as a mechanism. Multiple pulse voltammetry was also shown to be an effective means for minimizing electrode fouling for the intracellular measurement of dopamine (G270). Ewing et al. also wrote a general review on the topic of analytical chemistry in single nerve cells, which addresses the role of ultramicroelectrode voltammetry (G7).

In the area of extracellular voltammetry, Wightman and co-workers continued their fascinating investigations of exocytotic events at single bovine adrenal medullary cells in culture (G271). The shape of amperometric current spikes, monitored by carbon fiber disk electrodes positioned 5 pm from individual cells and analyzed using diffusional theory, was assigned to catecholamine release associated with single exocytotic events. Estimates of intravesicular catecholamine concentrations were made. Another impressive extracellular investigation was described in a paper by Kennedy et al. (G272). Chemically stimulated secretions (believed to be insulin) from individual pancreatic 0-cells were monitored amperometrically using ruthenium oxide/cyanoruthenate- modified carbon fiber electrodes. Current spikes were attributed to individual exocytotic events.

Immunological and Recognition-Based Electrochemistry. A clever new strategy for homogeneous electrochemical immunoassay was detailed by Degrand and co-workers (G273, G274) in which a cationic redox-labeled hapten partitions into a Nafion film where it can be detected voltammetrically. The antibody-hapten-label complex is unable to enter the film from the assay solution. This strategy was demonstrated in assays for amphetamine (G273) and phenytoin (G274) by attaching the redox label cobaltacenium. Detection limits in the nanomolar range were reported.

Two groups reported new results on the alkaline phosphatase/4-aminophenyl phosphate, an important system for electrochemical immunoassay. Yamaguchi et al. pushed the detection limits for 4-aminophenol, the enzymatic product of the reaction, to 500 pM by exploiting enzymatic recycling with diaphorase (G275). Subattomole detection of alkaline


phosphatase was reported. Thompson et al. examined buffer composition to optimize the same system and also reported subattomole detection, in this case for IgG-alkaline phosphatase (G276).

Huet and Bourdillon described a method aimed at electrochemical regeneration of the solid phase for automation of heterogeneous electrochemical immunoassays (G277). The key step, surface cleaning of glassy carbon via an oxidative potential step, could be applied for 150 cycles before mechanical resurfacing was required.

A more esoteric approach a t present, but one which holds promise for future development, is the use of mono-, bi-, and multibilayer membranes for sensing recognition events. Umezawa and co-workers reported further studies of coulometric ion channel sensors in which L-glutamic acid interaction with bilayer-incorporated glutamate receptor (GluR) ion channel proteins trigger an ioncurrent (G278). Amplification factors of IO5, detection limits of 30nM, and a high selectivity for L-glutamate over D-glutamate, were reported. In another approach, alkyl-derivatized cyclodextrin (the “host”) was incorporated into a monolayer (G279). By subsequently monitoring the electrochemistry of channel-permeable p - quinone, detection of channel blocking molecules (the “guest”) was observed. A different approach to sensing is being explored by Nikolelis and Krull, who monitor transient changes in the electrochemical properties of bilayer membranes as a result of biological interactions. Small transient ion currents were detected when thyroxin interacted with BLM that contained the antibody protein, due to alterations in the double-layer structure (G280).

Another novel example to sensor design based on receptor binding was provided by Wang et al. (G281). In this approach, multilayers of tyrosine hydroxylase deposited on a gold electrode by L-B technology were used to preconcentrate phenothiazine drugs before detection by stripping voltammetry.

Miscellaneous Bioelectrochemical Studies. Bard and co- workers described the application of scanning electrochemical microscopy to thecharacterization of surface enzyme reactions (G282). By using a microelectrode to monitor redox feedback of a soluble mediator, the catalytic oxidation of glucose by immobilized glucose oxidase could be detected.

In the complex area of microbial biofilms, which was not covered in this review, one particular article that may be of interest to bioelectrochemists concerned the monitoring of biofilm formation using a quartz crystal microbalance (G283).

Although a separate section on membranes was not created for this review, there are a number of relevant papers scattered throughout it. One more is the paper by Plant in which biomimetic membranes were created by self-assembly of a phospholipid/alkanethiolate bilayer on gold electrodes (G284).

H. CHARACTERIZATION OF REDOX REACTIONS Electron-Transfer Mechanisms. The algorithms that have

been developed over the years have become powerful techniques for the elucidation of electron-transfer mechanisms. The application of these techniques to actual mechanistic studies has grown as instrumentation has become more sophisticated and computers have become more powerful. In particular, the fast scan rates that are accessible by ultramicroelectrodes

have enabled the electrochemist to utilize a wide time scale for the study of electrochemical reactions. For example, Bond et al. ( H Z ) examined theoxidation of mer-W(CO)3(pI-dpm)- (112-dpm) to mer-W(CO)2(p2-dpm)12+ over a wide range of scan rates and electrode surfaces. Under most conditions, a single two-electron wave was observed. But, with the scan rates accessible by a 3-pm microelectrode, two one-electron waves were observed, due to the presence of an unstable intermediate. A two-electron wave was also examined by Pierce and Gieger ( H 2 ) . The electrochemical reduction of bis(hexamethylbenzene)ruthenium(II) occurred in either a single two-electron wave or two one-electron waves, depending upon experimental conditions. Digital simulation was used to determine the E O , k,, and a values for each step using scan rates between 0.4 and 100 V/s. Huang and Gosser used cyclic chronoamperometry and cyclic voltammetry to determine the kinetic parameters in the E& reduction of methylcobalamin in D M F (H3) . Andrieuxet al. ( H 4 ) reportedon improvements and estimation of precision in the cyclic voltammetry determination of rate constants and activation parameters of coupled first-order reactions. This work was then applied to halide cleavage of chloroanthracene radical anions. The reductive cleavage of the nitrogen halide bond in aromatic N-halosultams was studied to determine controlling factors of stepwise vs concerted reductive cleavages ( H 5 ) .

Fast-scan cyclic voltammetry was used by Yang and Bard to study the initial stage in the electropolymerization of aniline in aqueous solutions ( H 6 ) and the dimerization of N,N- dimethylaniline in acetonitrile ( H 7 ) . Andrieux et al. ( H 8 ) used fast-scan cyclic voltammetry to measure the redox potentials of unstable couples such as thiophenoxide ions. The redox potentials were measurable a t ultramicroelectrodes even though the dimerization reaction rates varied from 2 X lo8 to 2 X 1 O l 0 M-I s-l. The square reaction scheme was observed by Bond et al. ( H 9 ) in the fac/mer isomerization a t electron transfer of a Cr(CO)3(q3-L) complex. Digital simulation of the steady-state and non-steady-state cyclic voltammograms allowed the elucidation of the mechanism. Digital simulation was also used to elucidate the kinetic parameters in the metal- hydride cleavage of trans-[FeH(CNR)(dppe)2]+ (HIO) , which involved an ECECE mechanism.

Accurate measurements of heterogeneous rate constants can provide important information about the electron-transfer events. Anxolabehere et al. ( H I I ) examined the standard rate constants for the iron(I)/iron(“O”) wave for a series of iron porphyrins. By using the Marcus-Hush model, they found that the rate-controlling factor in these fast reactions was solvent reorganization. Brielbeck et al. ( H I 2 ) studied the heterogeneous and self-exchange rate constants for a series of fully a-methylated cycloalkane- 1,2-diones. They explained the significant changes in heterogeneous rate constants by the significant reorganization energy required by the cyclic 1,2- diones. Even greater changes were observed by Nelsen et al. ( H I 3 ) for conformationally protected hydrazines, which yielded electrochemically irreversible electron-transfer processes.

The electrochemistry of organic compounds continues to be a fruitful area of research, driven by their importance in electroanalytical methods and by a need to understand the structure and reactivity of unstable

Organic Electrochemistry.


organic intermediates. A significant number of articles appeared over the past two years on the oxidation of carbohydrates. Marioli and Kuwana ( H I 4 studied the electrochemical oxidation of carbohydrates at copper electrodes in alkaline solutions using cyclic voltammetry and rotating ring disk electrode experiments. I t was demonstrated that the important step in the oxidation was the interaction of the carbohydrate with the oxide/hydroxide layer covering the electrode. Oxidation beyond gluconic acid was observed and involved C-C bond cleavage. Burke and Ryan also showed that the hydrous oxide layer was important in the oxidation of glucose at a gold electrode (HI5). Electrochemical and polarimetric techniques were used in the oxidation of D-glucose on palladium (HI6). Saccharose oxidation was examined for its potentiality as a raw material for electrosynthesis (HI7). Chromatographic analysis of the electrolyzed solutions led to the identification of numerous monocarboxylic acids, some of them resulting from the breaking of the C-0-C bond. Surfaces modified with adatoms such as lead, thallium, or bismuth were active in the oxidation of glucose. The electrocatalytic properties depended upon the adatoms, with bismuth leading to significant amounts of glucuronic acid (H18). Lead adatoms on platinum also led to the selective oxidation of D-gluconic acid to oxalic, tartaric, and 5-keto- D-gluconic and D-glucuronic acids (HI 9).

Another class of compound reactions for which there was significant mechanistic activity was the reduction of nitro compounds. Ruhl et al. (H20) studied the reduction of some a-substituted nitroalkanes. The reduction of 2,2-dinitropro- pane led to a nitronate and nitrite by an ECE/DISPl mechanism. The nitronate that was formed reacted with starting material to form nitrite and a uic-dinitro dimer. By contrast, 1 -nitro-cyclohexyl-p-tolyl sulfone reduced by cleavage of the C-S bond to eject p-toluenesulfinate. Laviron et al. (H21) studied the reduction of 4-nitropyridine in solutions with acidities that varied from strongly acidic to pH 9.6. Three main reduction steps occurred: the nitro compound was reduced (2e-) to the dihydroxylamine, the dihydroxylamine dehydrated to give the nitroso compounds, and then the nitroso compound was reduced (2e-) to the hydroxylamine. The global reaction was of the ECE type and was analyzed using the theory of Nadjo and Saveant. Danciu et al. (H22, H23) examined the electroreduction of 4,4f-dinitrodibenzyl in water/ alcohol solutions. On mercury, the reduction occurred in two steps consisting of one- and three-electron transfers for each nitro group. Baumane et al. (H24) studied the mechanism and products of the electrochemical reduction of 4-(nitro- phenyl)-substituted 1 ,Cdihydropyridines. The reduction on mercury led to free radicals of nitro- and nitrosobenzene, and the dihydropyridine itself was only reduced if the compound was N-substituted. Dumanovic et al. (H25) examined 1-nitropyrazole and found that the reduction in acidic media led to cleavage of the N-N bond and the formation of nitrous acid. At pH >4, the nitro group was reduced to form a nitrosamine. Mirallesroch et al. (H26) examined the electrochemical conversion of a-nitrobenzylic compounds into the corresponding oximes.

Anne et al. (H27, H28) examined the electrochemistry of synthetic analogues of NADH and NAD dimer analogues. Medebielle et al. (H29) investigated the perfluoroalkylation

of pyrine and pyrimidine bases by electrochemically induced SRNI substitution. Combellas et al. (H30) carried out selective substitutions of 1,4-dichlorobenzene with 2,6-di-tert-but- ylphenoxide using the electrochemically induced S R N ~ mechanism. Mortensen et al. ( H 3 I ) studied the voltammetry of highly reduced oligoanthrylene systems and were able to generate the tetraanion of all the species studied. Cleghorn and Pletcher reported on the mechanism of the electrocatalytic hydrogenation of organic molecules at palladium black (H32) and palladium on nickel cathodes (H33). Mahdavi et al. (H34) examined the electrocatalytic hydrogenation of phenanthrene at Raney nickel electrodes. The electrochemical fluorination of benzene was carried out at +2.5 V in acetonitrile using tetraalkylammonium fluoride salts (H35).

Delgado et al. (H36) examined the electrochemistry of an alkali metal complex of quinone crown ethers and showed that the formation constants with the alkali metal with the attached crown ether varied with the redox state of the quinone. The binding of the alkali metal was qualitatively and quantitatively different from simple ion pairing. Urove and Peters (H37) examined the electrochemical reduction of cyclohexanecarbonyl chloride at mercury cathodes. Pritts et al. (H38) reported on a method to quantitatively determine volatile products formed in the electrolysis of organic compounds. Wandlowski et al. (H39) studied the electrochemical oxidation of 2,6-dichloro- 1,4-phenylenediamine. Potential step and digital simulation of the voltammetric data was used to determine the kinetic parameters.

Organometallic Electrochemistry. Redox-induced changes in the conformation, bonding, or solvation of the metal atom of a complex can be readily probed by the use of electrochemical techniques. Electron-transfer-induced isomerization of cobalt, nickel, and palladium cyclooctatetraene complexes was examined by Geiger et al. (H40) . The Ni and Pd complexes retained their 1,5-conformation upon reduction, while the Co complex underwent rapid isomerization to the 1,3-isomer in the 19e-species. The differences were explained by the role played by the ligand vs metal composition of the redox orbital. Osella et al. reinvestigated the electrochemical behavior of the Coz(CO)b(ethynylstradiol) complex and found evidence of efficient recombination of the electrogenerated fragments (H41). They also found electrochemical evidence for the reorientation of alkynes on trimetallic clusters during a two-electron reduction (H42). Karpinski and Kochi (H43) used electron-transfer chain (ETC) catalysis in the electrochemical deligation of bis(arene)iron(II) dications. Mecha- nistic studies were carried out using normal and reverse-pulse voltammetry. Sanaullah et al. (H44) used chemical and electrochemical methods to examine the redox-associated conformation changes in the bis( 1,4,7-trithiacyclononane)- copper(II/I) system. Electrochemical studies on niobocene- ketene complexes yielded redox-induced ketene fragmentation reactions (H45).

Solvent effects on the redox behavior of organometallic complexes were examined by several groups. Boudon et al. (H46) studied the effects of axial anions and solvent on the redox behavior of nickel complexes with C-functionalized tetraazamacrocycles. McDevitt and Addison (H47) examined medium effects on the redox properties of tris(2,2’-bipyridyl)- ruthenium complexes. The medium was also found to


modulate the two-electron activity of ferrocene metallocyclam conjugates (H48) . Mu and Schultz (H49) studied the effect of methanol binding on the redox potential and electron- transfer reactivity of chloro(tetrapheny1porphinato)manganese- (111).

The use of inert solvents such as liquid sulfur dioxide and/ or microelectrodes has enabled the voltage range to be extended, and highly reduced or oxidized species were observed. Liquid sulfur dioxide was used to study the oxidation of M(b~y)3~+complexes where M = Ni, Zn, and Cd (H50, H 5 1 ) . Very negative and very positive potentials wereused to generate Cp2C02+, Cp2C02-, and Cp2Ni2- (H52) . Ruthenium complexes are quite interesting in that they can undergo a large number of redox processes. Four one-electron-transfer steps were observed in the voltammetry of t runs-[R~(tpy)(O)~- (H20)l2+ (H53). Ruthenium(I1) complexes of 2,2’-bipyridine and 2-pyridylpyrazine were examined up to -3.1 Va t -54 OC in DMF using cyclic voltammetry ( H 5 4 ) . By the use of convolution techniques and digital simulation, it was possible to determine between 8 and 12 redox steps, depending upon ligation. Krejcik and Vlcek (H55) found that [(Ru- (bpy)2)zbpml4+ yielded 14 one-electron waves, 2 of which were metal based and 12 ligand based. Deblas et al. (H56) used pyridines with appended metallocyclam subunits as versatile building blocks to supramolecular multielectron redox systems. Reversible electrogenerated triply oxidized nickel porphyrins and porphycenes were reported by Kadish et al. (H57) , where they were able to generate a stable nickel(II1) x-dication.

The oxidation state of the metal atom in the electrogenerated complex was the focus of several studies. Guldi et al. (H58) investigated whether chromium(II1) porphyrins were reduced to Cr(I1) porphyrins or Cr(II1) porphyrin r-cation radicals. Kadish et al. (H59) examined the site of electroreduction of rhodium porphyrins. A very complex redox scheme was elucidated for the reduction of a-bonded iron(II1) porphyrins in noncoordinating solvents (H60) . Strojanovic and Bond (H61) examined the conditions under which the reduction of cobaltocenium cation could be used as a standard voltammetric reference process in organic and aqueous solvents. Kaminsky et al. (H62) reported on a reference electrode for organic solvents based on modified polyethylenimine loaded with ferrocyanide/ferricyanide.

Inorganic Electrochemistry. The electrochemistry of buckminsterfullerene and related complexes attracted the attention of many researchers. Xie et al. (H63) detected the hexaanions, c606- and C706-, using electrochemistry . The electrochemistry of c 6 0 was also studied in liquid ammonia (H64) . The kinetics and thermodynamics (H65) and the role of solvation (H66) in the electroreduction of c60 in aprotic solvents was investigated. Fast-scan cyclic voltammetry and scanning electrochemical microscopy (H67) were used to determine the kinetic parameters for the electroreduction of c 6 0 . An electrochemically reversible oxidation of c 6 0 and C70 was reported (H68) , as was the electrochemistry of C60H2

(H69) . Penicaud et al. (H70) electrocrystallized c 6 0 for the synthesis andcharacterization of (Ph4P)2C6oIX. Li et al. (H71) reported on unusual electrochemical properties of the chiral c 7 6 . Lerke et al. (H72) studied platinum, palladium, and nickel derivatives of buckminsterfullerene. Three to four waves

were observed, and the initial reduction led to the loss of the metal fragment. Koefod et al. (H73) studied the electrochemistry of an iridium buckminsterfullerene complex and found evidence for a c60 localized reduction.

Sudha et al. (H74) reported on electrochemical evidence for a two-electron-reduction process in a p-oxobis(F-acetate)- diruthenium(II1) complex with a terminal 1 -methylimidazole ligand. The electrochemistry of the incomplete cubane-type clusters, M3S4 (M = Mo, W), was examined (H75) , as well as some molybdenum mononitrosyl complexes containing oxobiphenyl ligands (H76) . The influence of pyridine substituents on binuclear rhenium(V) clusters was studied as a redox tuning procedure (H77) . Low-temperature voltammetry was used to study the reduction and oxidation of [ Re2(NSC)g] 2- (H78). The electrochemical reduction mechanism of a Ru3(C0)12 was investigated in considerable detail by voltammetric techniques (H79) . Cyr et al. (H80) studied the electrochemistry of boron-capped 99Tc-dioxime complexes. Choi et al. (H81) studied the electrochemical reduction of thionyl chloride by cyclic voltammetry, chronocoulometry, and chronoamperometry. Opekar and Langmaier (H82) reported a procedure for electrochemically controlled generation of carbon monoxide.

Activation of Small Molecules. The direct electrolysis or electrocatalytic activation of small molecules has been an active area of research. The largest area is probably the activation of carbon dioxide. These studies have involved both the direct reduction of carbon dioxide and the coupling of C02 to a substrate. Reports on theelectrocatalyzed reduction of carbon dioxide have included the catalysis by molybdenum-iron- sulfur clusters (H83) , nickel phosphine clusters ( H 8 4 ) , iron, cobalt, and nickel terdentate complexes (H85) , osmium bipyridyl complexes (H86) , and rhenium bipyridyl complexes incorporated into a coated Nafion membrane (H87) . Elec- trocatalytic surfaces have been reported for the direct reduction of carbon dioxide, such as ruthenium-titanium oxide (H88) , Cu + Au electrodes (H89) , Perovskite-type electrocatalysts (H90) , palladium (H91) or copper-modified palladium (H92) electrodes, and nickel electrodes a t high pressure (H93) . Carbon dioxide may also be electrochemically activated by the reductive addition of CO2 to quinones in acetonitrile (H94). Carbon dioxide can be coupled electrochemically by a nickel catalyst to 1,3-enynes (H95) , diynes (H96) , or alkenes (H97) . p-Anisic acid was formed from the reduction of p-iodoanisole at mercury in DMF, saturated with carbon dioxide (H98) . The electrocatalytic generation of C2 and C3 compounds was reported for the reduction of C02 on a cobalt complex- immobilized dual-film electrode (H99) . Kyriacou et al. (H100) examined the influence of CO? partial pressure and the supporting electrolyte cation on the product distribution. Naitoh et al. (H101) studied the electrochemical reduction of carbon dioxide in methanol a t low temperature.

The electroactivation of other small molecules have also been reported. Formaldehyde was oxidized on ultrafine gold particles, supported on glassy carbon substrates (H102). Methanol was electrooxidized on rhenium-tin oxide, platinum- tin oxide, and iridium-tin oxide, and the results were compared with the oxidation on platinum (H103). The electrocatalytic oxidation of methanol at PTFE-bonded electrodes was studied for a direct methanol/air fuel cell ( H 1 0 4 ) . Wong et al.


reported on the electrocatalytic oxidation of methanol (HZ05) and benzyl alcohol (HZ06) with a monooxoruthenium(V) complex. Cavalca et al. (HZ07) examined electrochemical modification of methanol oxidation selectivity and activity on a platinum single-pellet catalytic reactor. Gasteiger et al. (HZ08) studied methanol electrooxidation on well-characterized Pt-RN alloys. A quadruply aza bridged closely inter- spaced cofacial porphyrin was used to catalytically reduce dioxygen (HZ09). A rotating disk electrode was used to study the catalytic alkaline cyanide oxidation (HZZ0). A cobalt- (111)-mediated electrochemical oxidation was used to destroy chlorinated organics (HI Z I). F430-Model compounds, which contain nickel isobacteriochlorins, will dehydrohalogenate alkyl halides (H1Z2). Lojou et al. (HZZ3) examined the electroreduction of aryl halides in DMF on a cadmium- modified gold electrode. Che and Dong (HZZ4) applied ultramicroelectrodes to the electrocatalytic reduction of organohalides by metalloporphyrins. The electrocatalytic reduction of nitrate was studied with foreign lead adatoms (H115). Gur and Huggins (HZZ6) studied the direct electrochemical conversion of carbon to electrical energy in a high-temperature fuel cell.

Electrosynthesis. Electrosynthetic procedures have often been the impetus for detailed mechanistic studies by electrochemical techniques. The interplay between electrosynthesis and electroanalytical studies has been quite synergistic over the years. One area of active research is the direct electrosynthesis of solid material. Matsumoto et al. (HZ Z7) reported a new preparation method of Lac003 Perovskite using electrochemical oxidation. Wade et al. (HI 18) electrosynthesized ceramic materials and precursors, while Singh and Tanveer electrosynthesized (CdHg)Se (HZ 19, HZ 20) and (ZnCd)Se (HZ2Z). Dennison (HZ22) studied the cathodic deposition of CdS from aqueous solution. Roberts et al. (HI 23) investigated the mechanism and electrosynthesis of the superconductor Bal,K,Bi03. The direct dissolution of solid electrodes has also been used electrosynthetically. Halo and mixed-halo complexes of palladium(I1 and IV) were synthesized by the dissolution of a sacrificial palladium anode (HZ24). Cathodic dissolution of an AuTe2 electrode led to the formation of A ~ 3 T e 4 ~ - (HZ25).

Niyazymbetov and Evans (HZ26, HZ27) reported on the utility of carbanions and heteroatom anions in electroorganic synthesis. Biaryls and aromatic carboxylic acids were synthesized by palladium-catalyzed electrosynthesis using triflates (HZ28). Freshly metal coated electrodes were used to electrosynthesize 1,2-diketones by reduction of aromatic esters (HZ29). Gard et al. (H130) reported an efficient electrochemical method for the synthesis of nitrosobenzene from nitrobenzene. Momota et al. (HZ3Z) reported the electrochemical fluoridation of aromatic compounds in liquid R4NF.mHF. Wendt et al. (HZ32, HZ33) studied the anodic synthesis of benzaldehydes from the anodic oxidation of toluene. Amino acids were synthesized from a molybdenum nitride via nitrogen-carbon and carbon-carbon bond formation reactions involving imides and nitrogen ylides (H134). a- Nitrobenzylic acids were converted into oximes using mac- roscale electrolysis (HI 35). .The hydrodimerization of dimethyl maleate in methanol using an undivided cell was reported by Casanova et al. (HZ36). Franklin et al. (HZ37)

reported a method for the destruction of halogenated hydro- carbons accompanied by the generation of electricity.

Kunai et al. (HI 38) synthesized poly(disilany1ene)ethylenes by the electrolysis of bis(chlorosily1)ethanes. Chakravorti et al. (HZ39) reported the first electrosynthesis of transition metal peroxofluoro complexes (HZ 39). The selective electrosynthesis of (CH&C60 provided a novel method for the controlled functionalization of fullerenes (HZ40). Ferrate(V1) was prepared using an alternating current superimposed on the direct current (HZ4Z).

Micellar media can provide for some very interesting electrochemistry because of their ability to solubilize material in aqueous solutions. Nikitas (H142) reported a simple model for micellization and micelle transformations on electrode surfaces. Myers et al. (HZ43) studied solution microstructure and electrochemical reactivity. They examined the effect of probe partitioning on electrochemical formal potentials in microheterogeneous solutions. Abbott et al. (HZ44) studied electron transfer between amphiphilic ferrocenes and electrodes in cationic micellar solution, and the correlations between solvent polarity scales and electron-transfer kinetics, as applied to micellar media (HZ45). Gouniliet al. (HZ46) studied theinfluenceofmicelles and microemulsions on the one-electron reduction of 1 -alkyl- 4-carbomethoxypyridinium ions. The rate enhancement and control in electrochemical catalysis using a bicontinuous microemulsion was examined (HZ47), and this method was used to debrominate alkyl vicinal dibromides with neutral metal phthalocyanines (HZ48). An adsorbed film of cationic surfactant was used to dechlorinate 9-chloroanthracene (HZ49). Takisawa et al. (H150) reported on ultrasonic relaxation and electrochemical studies of the micellization of sodium decyl sulfate and decyltrimethylammonium bromide in glycerol/water mixtures. Phani et al. (HZ51) developed a microemulsion-based electrosynthesis of polyparaphenylene.

Micelles and Surfactants.

I . SPECTROELECTROCHEMISTRY The following survey is organized principally by technique.

While most spectroelectrochemical methods are well established, the cited articles either feature some experimental aspect of general interest or illustrate particularly well the versatility of a given technique.

On-line electrochemical mass spectroscopy, which is a powerful technique for the study of complex electrode reactions of small molecules, has been applied to a variety of problems. Included among these are studies of redox reactions of alcohols on Pt and Au (11-13) and on carbon-based electrodes (14). The working electrode of the latter study was made from PTFE-bonded carbon supporting Pt and Pt-Ru catalysts on Norit BRX. The working electrode of Munk and Skou was a microporous gold film on a commercial silicone rubber membrane (15). EC/MS has provided detailed mechanistic insight into the role of surface structure at single crystal electrodes during electrode reactions of unsaturated compounds (E152, E153, 16).

EC/MS studies have appeared on the oxidation of formaldehyde (Z7-110), acetonitrile (11 I), DMSO and sul- folane (Z12), and propylene carbonate (113,114). The latter article provides a good example of the use of isotopically labeled

Analytical Chemktry, Vol. 66, No. 12, June 15, 1994 407R

solvents (D2O and H2I80) to trace the origin of intermediates and products of the electrode reactions (114).

An on-line EC/MS study of 0 2 reduction under conditions of a methanol fuel cell allowed parallel reactions to be sorted out (115). Information on the reductive pathways for CH3- CC13 a t the Pt/H2S04 interface (116) and for nitrite at graphite-supported CuO electrodes (11 7) was obtained. A porous Ni-plated Teflon membrane allowed the electroless Ni-P deposition to be followed by mass spectroscopy (118). The oscillatory reaction involving bromate, malonic acid, and the Ce4+i3+ couple was followed by potentiometry and mass spectroscopy. The production of COz(,) tracked the potential oscillations in this system (119).

Several simplified designs of differential EC/MS interfaces have appeared (120, 121).

Articles continue to appear in which X-ray methods have been used to probe the electrode/solution interface. These techniques can give detailed specific information, i.e., bond lengths, in the best of circumstances, but require access to a synchrotron radiation source. Two new descriptions of cell designs for in situ X-ray spectroelectrochemistry were noted (122, 123). The latter employed transmission geometry through a drop of solution maintained on the electrode surface by capillary action.

Adlayer formation via UPD of metals are well-suited to study by X-ray methods. Recent systems examined include theUPDofPbandThonAu(l11) (124) ,CuUPDonPt( l I l ) (125) and Pt( 100) (126), Cu deposition on carbon-supported Pt (127), Ag UPD on Au( 11 1) (E234), and iodine adsorption on Pt single crystal electrodes (128). In the UPD study at Au( 11 l ) , it was found that the Au-Pb distance was potential dependent, while the Au-Th distance was not (124). In the surface EXAFS study of Cu UPD, chloride ion was shown to play an important role in the ordering of the adlayer (125).

In situ X-ray methods have been used to follow intercalation reactions of Moo3 (129), Li,CoOz (130), and V6OI3 (131) electrodes. In situ X-ray spectra demonstrated the conversion of cu-PbOz to the p-form on Pt substrates (132) and the formation of Cu20 layers by the reduction of Cu02’- in concentrated KOH (133). In situ XANES of Fe-26Cr stainless revealed peaks for Cr(V1) that could be correlated with the transpassive voltammetric wave (134). Near-edge EXAFS spectra demonstrated that disulfide bond scission occurred upon electroreduction of a sulfur polymer (135).

In situ X-ray methods have monitored surface roughness ofPt(l11) andAu(IOO)electrodes(Z36.137)andtheformation of oxides on dispersed Pt /C fuel cell electrodes (138).

Spectroelectrochemistry in the UV/visible region of the spectrum is routinely practiced in the characterization of inorganic, organic, and biological redox couples. On the theoretical side, Wei et al. have published several papers on spectroelectrochemistry under “long-path-length’’ conditions, i.e., with the light beam parallel to the working electrode (139-143). One of the papers contains theoretical expressions for derivative linear sweep and derivative cyclic voltabsorptometry, e.g., expressions for d(ABS)/dE],k, under thin-layer conditions (140). The case of semiinfinite linear diffusion was also addressed. The catalytic EC’ mechanism has also been treated under these conditions (144, 145). Zamponi et al. have presented derivative linear sweep voltabsorptometry

theory for surface waves and OTTLE cells (146). The relationship between the d(ABS)/dt vs E curve and the corresponding voltammetric parameter is one of equivalence in most situations.

A spectroelectrochemical sensor for Cl2 based on a planar optical waveguide was described (147). This novel device employed a thin Lu-biphthalocyanine film on IT0 that could be electrochemically reset to the reduced state. Oxidation of the film by dissolved chlorine, which was monitored at 950 nm, resulted in an integral signal that was linear in the 0-30 ppm range. The transmittance changes were detected using a transverse magnetically polarized evanescent wave. Wave- length modulation spectroscopy was used to obtain spectra of methylene blue and Co tetrasulfonated phthalocyanine couples on graphite electrodes (148). The instrument described had a resolution of ca. 0.002 absorbance unit.

Several papers on experimental aspects were noted. A simple procedure was given for the synthesis of SnO2 and the preparation of SnO2-coated I T 0 glass electrodes (149). An optically transparent carbon film electrode, with electrochemical properties similar to glassy carbon, was prepared by the pyrolysis of an aromatic anhydride on a quartz substrate (150). The general method of modifying I T 0 electrodes of Chen et al. deserves mention again (F88) . Salbeck has published two standard designs for thin-layer cells, in one of which only Teflon components contact the solution (151,152). Shimazu et al. performed simultaneous UV/visible spectroelectrochemistry and QCM (153). Optically transparent contacts to the quartz crystal were used in a transmission mode configuration.

Fluorescence spectroelectrochemistry was shown to be a sensitive method for the detection of intermediates and products of electrode reactions (154,155). These authors gave details of their flow cell, which was used with a commercial luminescence spectrometer. Littig and Nieman also obtained excellent sensitivity with an electrochemical FIA chemiluminescence method (156). Electrochemical reduction of 0 2 to H202 triggered the chemiluminescence of acridinium esters in a flow cell giving a LOD in the 10-fmol range. The sophisticated fluorescence imaging of electrode surfaces cited above can also be mentioned here (E115, E295).

Two simple cell designs for luminescence spectroelectrochemistry have appeared (157, 158).

Articles on ECL that were noted included a report that ultrasonic radiation markedly enhanced the ECL intensity in the R~(bpy)3~+/0xalate system (159) and the observation of the ECL of perylene in a room-temperature molten salt (160). A weak photoemission seen during the evolution of 0 2 a t Pt in water was assigned to the recombination of singlet oxygen molecules (161).

FT-IR spectroelectrochemical studies on adsorbed C O continue to give detailed information on the interfacial structure and electrode reactions. The spectra of Roth and Weaver indicated a terminal coordination of C O over a wide potential range at Pt/nonaqueous interfaces (162). Bands in the ATR-IR spectra of CO on Pt were assigned to a linearly bonded C O and possibly a multiply bonded species (163). FT-IR spectra of CO on Ni electrodes in KOH(,,) indicated oxidation via bridge-bonded C O to generate carbonate ions (164). Cation effects on the IR spectra of C O adsorbed on


Pt were interpreted in terms of an electrochemical Stark effect in which the cation altered the position of the outer Helmholtz plane (165). Quantum mechanical X, calculations, which assumed a Pt4 cluster as a model for the electrode surface, were used to calculate the potential dependence of uco at Pt electrodes (166).

C O coverages on Pt were obtained from FT-IR absorbance values after oxidation of C O to C02 in a thin-layer cell (E264).

Differences were noted between the in situ and the ex situ IR reflection absorption spectra of HSO4- adsorbed on P t ( l l1 ) (167). The in situ spectra indicated adsorption at positive potentials and a potential dependence of A,,,. Adsorption of CH3CN on gold was followed by subtractively normalized FT-IR spectroscopy which gave a picture of the double layer containing two types of CH3CN and H20 in the interfacial region (168).

In situ FT-IR spectroelectrochemistry was performed on cobalt electrodes in NaOH(,,, (169), Si single crystal wafer electrodes (170), and Ru electrodes in aqueous acid and alkaline solutions (171).

In several instances, in situ infrared spectroscopy has given information on the orientations of molecules at electrode surfaces. For example, anthraquinonedisulfonates adopted a flat orientation initially and then a more perpendicular configuration as the adsorption proceeded (172). Polarization modulation FT-IR spectra of thick phenazine and phenothiazine films indicated that most of the molecules were oriented either perpendicular (in one case) or parallel (in two cases) to the electrode surface (173). In situ reflectance IR spectra indicated that the very narrow CV wave seen for heptylviologen on Hg was due to a faradaic reaction (174).

While solution spectroelectrochemical studies have been generally omitted from this survey, attention will be called to the extensive set of data, including IR band assignments, for nine p-quinone molecules in five solvents (175). On the experimental side, a three-electrode IR optically

transparent thin-layer electrochemical cell was detailed that allowed minimal diffusionof 0 2 into thecell (176). Electrodes used in ATR spectroelectrochemical cells included a gold minigrid placed on the surface of a ZnSe element (177) and a BaF2 crystal coated with a 30-nm Au layer (178). A detailed description of the problems that arise in the use of Ge or GaAs crystals for ATR spectroelectrochemistry has appeared (179).

FT-IR external reflection spectroelectrochemistry has been carried out using a step-scanning, phase-modulated spectrometer and controlled-potential electrochemical modulation of the signal (180). Since Fourier frequencies due to movement of the interferometer mirror are reduced to zero in step- scanning spectrometers, cross-talk between the Fourier frequencies and modulation of the electrode potential is minimized. The feasibility of the technique was established for the surface oxidation of C O on Pt. For spectra obtained with more conventional instruments, simple trapezoidal integration of the EMIRS spectra led to improved spectra and more convincing peak assignments (181, 182).

In situ spectroelectrochemistry was performed using synchrotron radiation in the far-IR region, which is 100- 1000 times brighter than conventional black body radiation (183,184). The decomposition of C104- in an acid electrolyte

was indicated by the appearance of bands due to adsorbed chloride.

Real-time surface-enhanced Raman spectroscopy (SERS) of the electrooxidation of Pt, Rh, Ru, and Au surfaces was performed using a charge-coupled device detector. Raman bands in the 250-850-cm-l region were assigned to metal- oxygen vibrations; M-0 and M-OH vibrations were distinguished by the use of D20 solvent (185). SERS spectra acquired during the oxidation of CO at Au, Pt, and Rh films on gold substrates detailed the interrelations between C O and metal surface oxidation processes (186). In situ SERS of adsorbed oxygen on Ag was performed under a wide range of conditions on various supports, including YzO3-stabilized ZrO2 (187). SERS spectra were reported for oxide films at Ti and copper electrodes (188, 189).

Pemberton and co-workers have continued their studies of the orientation of adsorbed alcohol molecules at silver and gold electrodes (190-194). They deduced the orientations, which were generally potential dependent, from the relative intensities of the symmetric and the asymmetric C-H vibrations of the methyl and methylene groups in the adsorbates. Interestingly, their spectra indicated that the solvent structure and orientation were maintained upon emersion from butanol solvents (192).

SERS of adsorbed pyridine and related molecules continues to be a popular topic. Often perpendicular, or nearly perpendicular, orientations are reported (195-197), although SERS spectra of indole on roughened Ag were interpreted in terms of a parallel orientation (198). Articles appeared on SERS of pyridine adsorption on Cu and Ag (199), the effect of Pb UPD on pyridine adsorption on Cu electrodes (1100), and 4-mercaptopyridine adsorption at mechanically polished polycrystalline Pt (1101). A SERS study of coadsorbed nicotinic acid and 3-acetylpyridine on Ag featured detailed band assignments (1102).

The intensity of SERS spectra of pyridine on Ag, as activated in the usual fashion by redox cycling, was found to be related to the magnitude of the cathodic charge applied in the activation and was roughly independent of the anion (1103).

In situ SERS has been used to good effect to identify intermediates and products of electrode reactions. Systems studied recently include the oxidation of diphenylamine in CH3CN (1104, the oxidation of o-aminophenol(1105,1106), the surface redox chemistry of p-mercaptoaniline (1107), the oxidation of adsorbed sulfur on gold (1108), and the oxidation of pyrite in neutral solutions (1109). SERS spectra of the 43N'+ cation radical in CH3CN were obtained in a flow cell without interference from dimeric products (11 10). SERS of organic sulfides was carried out at a rotating silver electrode in order to eliminate experimental artifacts due to photo- reactions (11 11). Other SERS electrochemical studies included electrodeposition of Ag from a cyanide bath (1112), the Cu/CuSCN electrode (1113), and Ni electrodes in the presence of electrodeposited Ag (11 14).

Time-resolved SERS was impressively performed in a pulse mode at low power in order to detect intermediates of electrode reactions on the nanosecond time scale (11 15). Time-resolved SERS spectra for the reduction of heptylviologen on Ag indicated the existence of nucleation phenomena at short times (11 16).

Analytical Chemistry, Vol. 66, No. 12, June 15, 1994 409U

In situ Raman spectra of Zn-phthalocyanine films on Au and glassy carbon electrodes were obtained with a confocal spectrometer. A significant aspect of this study was that the irradiated spot on the electrode surface had a diameter of less than 1 ym (1117).

Simonet and co-workers have used spin traps to detect radical intermediates in the electrochemical reduction of several species (1118, 11 19). For the reduction of (C6Hs)dP+ in nonaqueous solvents, it appeared that the CsH5' radical was not an intermediate. ESR was also used to follow the intercalation of lithium into V2O5 cathodes (1120). The time frame accessible in the ESR-electrochemistry experiment was ca. 1 s in the study of Dunsch and Petr (1121).

13C NMR spectra were obtained for I3C-enriched CO on Pt-black surfaces under potential control (1122). Line narrowing and chemical shifts were seen associated with changes in the CO bonding at the surface. Another original spectroelectrochemical study was the in situ determination of atomic magnetic susceptibility using a nonspinning cell that operatedin the boreof a 400-MHzNMR spectrometer (1123). The test system for this study was a 0.1 M Fe(CN)63-/4COUpk in D20 solution.

Several applications of ellipsometry to electrochemistry have been described by Hamnett (11 24). Ellipsometric transients were followed during adsorption of thiols on gold, growth of metal oxide films, and growth and switching of polymer films. The time scale was relatively slow, on the order of seconds, but the author predicted advances in instrumentation that would allow measurements in the millisecond range, as well as spatial resolution of ca. 10" cm2. Chao et al. measured effective dielectric constants for the electrode/solution interface at single crystal electrodes using an ellipsometry method (1125).

Electrochemical quartz microbalance methodology has proved to be useful for the study of a variety of interfacial processes as evidenced by the many applications to surface electrochemistry and polymer film electrodes cited above. Several recent papers have addressed experimental artifacts that can arise with this technique. The problem of nonuniform mass sensitivity across a QCM electrode surface was treated authoritatively by Hillier and Ward (1126). Bacskai et al. have also considered the QCM response for uneven coatings of polymer films (1127). The effect of surface microstructure on the QCM response was analyzed, and the analysis applied to roughened Ag/AgCI surfaces (1128). Frequency shifts on the order of a few hertz (e20 Hz) were seen for EQCM experiments with nonadsorbing couples for 5-MHz AT-cut quartz crystals (11 29). These shifts were assigned to changes in the density and viscosity of the depletion layer at the electrode surface.

EQCM of poly(bithiophene) electrodes indicated that rigid films were electrodeposited from CH3CN up to 50 nmol/cm2 electroactive sites and that the Sauerbrey equation was valid (1130). For thicker films departure from rigidity was seen.

The dependence of the superficial energy of a QCM oscillator on elastic strain and stress predicted by the Lippmann equation was experimentally verified (1131). By use of a dual QCM oscillator, connected to the EQCM via a pressure chamber, the effects of mass and surface energy could be separated.

A fast EQCM apparatus was used to study ion-exchange reactions of poly(pyrro1e); a resolution of a few nanograms in a measuring time of 1 ms was achieved (1132). The EQCM experiment was performed with 30-MHz AT-cut quartz crystals that had been chemically milled to produce a thin disk surrounded by a thick quartz ring (1133). The resulting high-frequency operation afforded significantly increased sensitivity.

J. INSTRUMENTATION Circuit diagrams have been published for an instrument

that simultaneously measured the electrode potential and the resistance of an electrolyte solution ( J I ) and for several potentiostats (J2-J4). The single op amp potentiostat of Amatore and Lefrou allowed for ohmic drop compensation at sweep rates up to 300 kV/s. An instrument for digital ac voltammetry has also been described (J5).

A Fourier transform impedance spectrometer, which operated in the frequency range 10-3-105 Hz, was described in some detail (56). Schefold gave details of an instrument for intensity-modulated photocurrent spectroscopy that employed a red LED as the light source ( J 7 ) . It was used in a nice study of charge transfer at p-InP single crystal electrodes. A simple impedance instrument was described for measurement of double-layer capacities ( J 8 ) .

Several experimental apparatuses designed for operation under extreme conditions were noted. These include an automatic setup for impedance measurements on two-electrode cells over a frequency range from to lo7 Hz and a programmed temperature range from room temperature to 1100 K ( J9 ) . Pressure effects on electrochemical potentials were measured with a cell that withstood pressures up to 10 kbar (J10). The Ag/AgCl reference electrode potential was found to be relatively pressure insensitive in this study. The high-pressure cell of Sachinidis et al. operated at pressures up to 1.5 kbar ( J I 1) . Cyclic voltammograms of several metal/ metal oxide couples were obtained at 700-900 OC in an yttria- stabilized zirconia oxygen ion conducting electrolyte (J12). As noted above, low-temperature electrochemistry has been performed at superconducting UMEs; details of a cell design were given by Green et al. (E346) .

Several cleverly designed flow cells have been described including a RVC spectroelectrochemical detector for LCEC ( J 1 3 ) , a carbon fiber cell (514, and a flow reactor containing mosaics of ion-exchange membranes and bipolar metal electrodes (J15). In the latter device, electrons and ions were transported in the same or opposite directions by the driving forces of redox potential and concentration gradients.

A technique called "current spike polarography" was used to study aqueous/air interfaces and thin films of solution held in a silver ring (J16). In the latter situation, a small volume of solution (0.01 mL) was positioned just below a DME capillary and the i-E-t transients were measured as the Hg drop touched and fell through the solution. Comparison of the zero current potential with that of the bulk solution polarogram gave an estimate of the surface potential of the electrolyte solution.

Reference electrodes recommended for nonaqueous solvents included the 13-/1- couple in CH3CN (J17) , a cross-linked poly(ethy1eneimine) film electrode loaded with Fe(CN)63-/4


(JZ8) , and Mg(Hg) amalgam in DMF (J19) . An electrode, consisting of 6 Ag/AgCl wire embedded in PTFE/alumina/ KCl layers pressed into pellet form, performed nicely as a pressure-insensitive reference electrode for in situ natural water studies (J20). The standard potentials of glass electrodes with internal solutions of zwitterion buffers were reported to vary linearly with temperature over the range 5-50 OC (J2Z). Construction of a miniature, needle-type, working electrode/ reference electrode assembly, 0.5 mm in diameter, for sensing glucose was described (522). A dual-reference electrode consisting of a SCE and a Pt wire connected by a 0.1-pF capacitor was recommended on the basis of its high impedance response (523).

Tieman et al. employed a three-electrode sensor made by screen printing Pt onto a ceramic substrate (J24), and a very simple procedure for sealing gold into glass using glass soldering powder was reported (J25).

Experimental details were given for fitting DMEs with commercially available PTFE tips for use in media that attack glass capillaries (J26). The same group reported on a simple, automatic HDE, DME, SHDE apparatus (J27). A Hg film electrode covered by a cellulose membrane was used to quantify metal species directly on a TLC plate (J28).

Several interesting descriptions of porous electrodes have appeared. The gas-sensing electrodes of Tierney and Kim had fast response times due to the absence of a semipermeable membrane and the fact that the gas molecules came directly in contact with the working electrode (J29). They used two types of porous substrates: an alumina ceramic and a micromachined silicon wafer with an array of 10-pm holes. Microporous gold films, which replicated the structure of an anodic porous alumina template, had a narrow distribution of pore diameters around a value of 100 nm (J30) . Tang and Chan constructed gas diffusion electrodes by electrodeposition of Ag on commercially available Ni mesh (J31) . An open pore network Pt electrode was stabilized by a procedure that involved heating Pt and yttrium oxide powders a t T I 1500 “ C (J32). To drive home the reoccurring observation that little is new these days, a fascinating description of a French patent granted to P. L. Hulin in 1893 for a “flow-through porous electrode” is recommended reading (J33) .

A technique for iR, compensation involved measurement of the ac impedance at high frequency and adjustment of the applied potential under computer control by thevalue of Id&

( J 3 4 ) . The measurement and correction routine was com- pleted in ca. 2 ms using a 12-bit, 10-ps ADC and a 486 PC. Details of software packages for interfacing PAR 273 and 174 potentiostats have been published (535, J36).

Andrieux et al. found that digital and analog filtering of CV i-E data, while decreasing random error on peak potential measurements, resulted in increased systematic error (J37).

LITERATURE CITED

A. BOOKS AND REVIEWS

(A l ) (A2) (A3) (A4) (A5) (A6)

Ryan, M. D.; Chambers, J. Q. Anal. Chem. 1992, 64, 79R-116R. Fogg, A. Analyst 1992, 177, 1801. Zuman, P. Analyst 1992, 177, 1803-1809. Eccles, 0. N. Crlt. Rev. Anal. Chem. 1991, 22, 345-380. Osteryoung, J. Acc. Chem. Res. 1993, 26. 77-83. VanLeeuwen, H. P.; Buffle, J.; Lovric, M. Pure Appl. Chem. 1992, 64, 1015- 1028.

Koryta, J. Ions, Electrodes andMembranes, 2nd ed.; J. Wiley & Sons: New York, 1991. Kapoor, R. C.; Aggarwal, B. S. Principles ofPolarcQraphx Wlley: New York, 1991. Runo, J. R.; Peters, D. 0. J. Chem. Educ. 1993, 70, 708-713. Gileadi, E. Electrode Klnetlcs; VCH Publlshers, Inc.: New York, 1993. Bard, A. J.; Abrub, H. D.; Chldsey, C. E.; Faulkner, L. R.; Feldberg, S. W.: Itaya, K.: MaJda, M.; Melroy. 0.; Murray, R. W.; Porter, M. D.; Sorlaga, M. P.; Whlte. H. S. J. Phys. Chem. 1993, 97, 7147-7173. Bard, A. J. Pure Appl. Chem. 1992, 64. 185-192. Modem Aspects of Electrochemistry; Bockrls, J. O’M., Conway, 8. E., Whlte, R. E., Eds.; Plenum: New York, 1993; VoI. 25. Modern Aspects of Electrochemistry; Conway, B. E., Bockrls, J. O’M., Whlte, R. E., Eds.; Plenum: New York, 1992; Vol. 23. ModemAspects ofEktctroahemlstry; WMe. R. E., Conway, B. E., Bockris, J. OM., Eds.; Plenum: New York, 1993; Vol. 24. Electrochemlttyln Transitkn From the 2W, to the 2 7st Centwy; Murphy, 0. J., Srlnhrasan, S., Conway, B. E., Eds.; Plenum: New York, 1992. Advances In Electrochemlcl Sclence and Englneerlng, Gerlscher, H., Tobias, C. W., Eds.; VCH Publlshers: Welnhelm, 1992; Vol. 2. AdswptionofMoleculesatMetalElectrodes; Llpkowskl, J., Ross, P. N., Eds.; VCH, Inc.: New York, 1992. StructureofEfectrifled Interfaces; Lipkowskl, J., Ross, P. N., Eds.; VCH Publishers: New York, 1993. Comprehenslve Chemlcal Klnetlcs. Reactions at the Liquid-SolU Interface: Compton, R. G., Ed.; Elsevler: Amsterdam, 1989; Vol. 28. Electrlfied Interfaces h Physlcs, Chemism and Biology; Guldelll, R., Ed.; Kluwer Academlc Publlsher: Hlngham, MA, 1992. Weaver, M. J. Chem. Rev. 1992, 92, 463-480. Galus, Z. Pure Appl. Chem. 1991, 63, 1705-1714. Saveant, J.-M. Acc. Chem. Res. 1993, 25, 455-461. Trasattl, S. Electrochim. Acta 1992, 37, 2137-2144. Parsons, R.; Rltzoulls, 0. J. Electroanal. Chem. 1991. 378, 1-24. Soriaga, M. P. Frog. Surf. Sci. 1992, 39, 325-443. Appleby, A. J. J. Electroanal. Chem. 1993, 357, 117-179. Bockris, J. O M ; Khan, S. U. M. Surface Electrochemishy: A Molecular Level Approach; Plenum: New York, 1993. Koelle, U. New J. Chem. 1892, 76, 157-169. Pure Appl. Chem. 1991, 63, 1759-1779. Trasattl. S.; PeMi, 0. A. J. Electroanal. Chem. 1992, 327, 353-376. Techniques for Characterlzatlon of Electrodes and Electrochemical Processes; Varma. R.. Selman, J. R., Eds.; Wlley: New Yofk, 1991. Christensen, P. A. Chem. Soc. Rev. 1992. 27, 197-208. Buttry, D. A.; Ward, M. D. Chem. Rev. 1992, 92, 1355-1380. Hillman, A. R.; Loveday, D. C.; Swann, M. J.; Bruckenstein, S.; Wllde,

Volk, K. J.; Yost, R. A.; BraJter-Toth, A. Anal. Chem. 1992, 64, 21A- 33A. Ashley, K. Talanta 1991, 38, 1209-1218. Rajeshwar. K.; Lema, R. 0.; de Tacconl, N. R. Anal. Chem. 1992, 64,

C. P. Analyst 1992, 1251-1257.

429A-441A. E&troana!MzdChemishy, Bard, A. J., Ed.; Marcel Dekker: New York, 1993: Vol. 18. Inzen, G. Acta Chlm. Hung. 1992, 729, 365-382. Mcroekctrotlas: mory and Applications. Proceedings of NATO AdvancedSW Inst&&, A h , Portbgal, May 1426,1990; Montenego, M. I., Queiros, M. A,, Daschbach, J. L., Eds.; Kluwer Academic Publishers: Hingham, MA, 1991. Heinze, J. Angew. Chem., Int. Ed. Engl. 1993, 32, 1268-1288. MolecularDeslgn of Electrode Surfaces; Murray, R. W., Ed.; Techniques of Chemistry Series XXII; John Wlley & Sons: New York, 1992. Forster, R. J.; Vos, J. G. Compr. Anal. Chem. 1992, 27, 465-529. Zagal, J. H. Coord. Chem. Rev. 1992, 179, 89-138. Imisides, M. D.; John, R.; Riley, P. J.; Wallace, G. G. Electroanalysls

Labuda. J. Sel. Electrode Rev. 1992, 74, 33-86. Cox, J. A.; Jaworski, R. K.; Kulesza, P. J. Electroanalysis 1991, 3.

Electrwesponsive Mdecular 8nd Polymeric Systems; Skothelm, T. A., Ed.; Marcel Dekker, Inc.: New York, Basel and Hong Kong. 1991; Vol. 2. Mlrkln, C. A.; Ratner, M. A. I n Annual Review of Physical Chemistry; Strauss, H. L., Ed.; Annual Reviews: Palo Alto, CA, 1992; Vol. 43. McDevitt, J. T.; Riley, D. R.; Haupt, S. G. Anal. Chem. 1993, 65, 535A- 545A. Bruce, P. 0.; Vlncent, C. A. J. Chem. SOC., Faraday Trans. 1993, 89,

Lapkowskl, M. Mater. Scl. 1991, 77, 7-14. Curran, D.; Grimshaw, J.; Perera, S. D. Chem. Soc. Rev. 1991. 20,

Alvarez-Icaza, M.; Bllltewski, U. Anal. Chem. 1993, 65, 525A-533A. Heller, A. J. Phys. Chem. 1992, 96. 3579-3587. Bardelettl, 0.; Sechaud, F.; Coulet, P. R. Bloprocess Technol. 1991, 75, 7-45. Blosensws: A PractlcalApproach; Cass, A. E. 0.. Ed.; Oxford Unlverslty Press: New York, 1990. Alzawa, M. Anal. Chlm. Acta 1991, 250, 249-256. Wring, S. A.; Hart, J. P. Analyst 1992, 777, 1215-1229. Hlldkch, P. I.; Green, M. J. Analyst 1991, 716, 1217-1220. Ewlng. A. G.; Strein, T. 0.; Lau, Y. Y. Acc. Chem. Res. 1992, 25, 440-447. Smyth, W. F. Voltammetrlc Determination of Molecules of Biologlcal Slgnlflcance; Wiley: Chlchester, 1992. Casskfy, J. F. Compr. Anal. Chem. 1992, 27, 1-89. van den Berg, C. M. G. Anal. Chim. Acta 1991, 250, 265-276. Tur’yan, Y. I. J. Electroan81. Chem. 1992, 338, 1-30.

1991, 3, 878-889.

869-877.

3187-3203.

391-404.


Barisci, J. N.; Riley, P. J.; Wallace, G. G. Compr. Anal. Chem. 1992, 27, 71-113. Gosser, D. K., Jr. Cyclic Votfammerty: Simulation and Analysis of Reaction Mechanisms; VCH Publishers, Inc.: Deerfield Beach, FL, 1993. Organic Electrochemistry. An Zntroduction and a GuMe, 3rd ed.; Lund, H., Ed.; Marcel Dekker: New York, 1991. Electroorganic Synthesis. Festschrlff for ManuelM. Baizec Little, R. D., Weinberg, N. L., Eds.; Marcel Dekker: New York, 1991. Shono, T. Elechoorganic Synthesls: Academic Press, Ltd.: London, 1991. Niyazymbetov, M. E.; Evans, D. H. Tetrahedron 1993, 49, 9627-9688. Silvestri, G.; Gambino, S.; Filardo, G. Acta Chem. Scand. 1991, 45,

Electrochemical and Electrocafalytic Reduction of Carbon Dioxide; Sullivan, B. P., Ed.; Elsevier: Amsterdam, 1993. Karpinets, A. P.; Bezuglyi, V. D. Elektrokhimlya 1992, 28, 638-653. Watanabe, T.; Kobayashi, M. Chlorophylls 1991, 287-315. Wayner, D. D. M.; Parker, V. D. ACC. Chem. Res. 1993, 26, 287-294. Koval, C. A.; Howard, J. N. Chem. Rev. 1992, 92, 411-433. Gratzel, M. Coord. Chem. Rev. 1991, 111, 167-174. Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Muller, E.; Liska, P.; Vlachopoulos, N.; Gratzel, M. J. Am. Chem. SOC. 1993, 115,

Jung, K. H.; Shih, S.; Kwong, D. L. J. Electrochem. SOC. 1993, 140,

Brodsky, A. M. I n Excess Electrons in Dielectric Media; Ferradini, C., Jay-Gerin, J.-P., Eds.; CRC Press: Boca Raton, FL, 1991; pp 349-365. New Trends in Electrochemistry; Decker, F., Scrosati, B., Eds.; Electrochim. Acta 1993, 38, 1-157. J. Electroanal. Chem. 1993, 355, 1-20. J. Electroanal. Chem. 1993, 357, 1-46.

987-992.

6382-6390.

3048-3064.

B. MASS TRANSPORT

(BI) Mirkin, M. V.; Bard, A. J. Anal. Chem. 1992, 64, 2293-2302. (82) Lavagnini, I.; Pastore, P.; Magno, F. J. Elecfroanal. Chem. 1992, 333,

1-10, (B3) Fieischmann, M.; Pons, S.; Daschbach, J. J. Elechoanal. Chem. 1991,

317, 1-26. (84) Kalapathy, U.; Tallman, D. E.; Hagen, S. J. Elecfroanal. Chem. 1992,

325, 65-8 1. (85) Oldham, K. 8. J. Electroanal. Chem. 1992, 323, 53-76. (B6) Bender, M. A.; Stone, H. A. J. Elechoanal. Chem. 1993, 351, 29-55. (87) Mirkin, M. V.; Bard, A. J. J. Elechoanal. Chem. 1992, 323, 1-27. (BE) Mirkln, M. V.; Bard, A. J. J. Electroanal. Chem. 1992, 323, 29-51. (B9) Brodsky, A. M.; Burlatsky, S. F.; Reinhardt, W. P. J. Electroanal. Chem.

1993, 358, 1-20. (B10) Lavagnini, I.; Pastore, P.; Magno, F.; Amatore, C. A. J. Elechoanal.

Chem. 1991, 316, 37-47. (B11) Amatore, C. A.; Fosset, B. J. Electroanal. Chem. 1992, 328, 21-32. (812) Oldham, K. B. J. Electroanal. Chem. 1992, 337, 91-126. (813) Myland, J. C.; Oldham, K. B. J. Elechoanal. Chem. 1993, 347, 49-91. (814) Smith, C. P.; White, H. S. Anal. Chem. 1993, 65, 3343-3353. (815) Oldham, K. B. Anal. Chem. 1992, 64, 646-651. (B16) Che. G.: Dona. S. Electrochim. Acta 1992, 37, 2695-2699, 2701-

2705. Zhuang, Q.; Chen, H. J. Elecfroanal. Chem. 1993, 346, 29-51, 471- 475. Daasbjerg, K. Acta Chem. Scand. 1993, 47, 398-402. Lavagninl, I.: Pastore, P.; Magno, F. J. Elechoanal. Chem. 1993, 358, 193-201. Che, G.; Dong, S. Electrochim. Acta 1993, 38, 1345-1349. Yang, H.; Wipf, D. 0.: Bard, A. J. J. Elechoanal. Chem. 1992, 331,

Bond, A. M.; Feldberg, S. W.; Greenhill. H. B.; Mahon, P. J.; Coiton, R.; Whyte, T. Anal. Chem. 1992, 64, 1014-1021. Mesaros, S.; Rievaj, M.; Bustin, D. Collect. Czech. Chem. Commun. 1993, 58, 281-290. Wikiel, K.; Dos Santos, M. M.; Osteryoung, J. Electrochim. Acta 1993, 38, 1555-1558. Wikiel, K.; Osteryoung, J. Electrochim. Acta 1993, 38, 2291-2296. Borkowskl, M.; Stojek, Z. Elechoanalysis (N.Y.) 1992, 4, 615-621. Wiedemann, D. J.; Kawagoe, K. T.; Kennedy, R. T.; Clolkowski, E. L.; Wightman, R. M. Anal. Chem. 1991, 63, 2965-2970. Strein, T. G.; Ewing, A. G. Anal. Chem. 1992, 64. 1368-1373. Nyholm, L.; Wikmark, G. Anal. Chim. Acta 1992, 257, 7-13. Hsueh, C. C.; Brajter-Toth, A. Anal. Chem. 1993, 65, 1570-1574. Peng, T.; Lu, H.; Liu, G.; Cao, Y. Anal. Lett. 1992, 25, 795-805. Tabei, H.; Morita. M.; Niwa, 0.; Horiuchi, T. J. Electroanai. Chem. 1992, 334, 25-33. Frisbie, C. D.; Fritsch-Faules, I.; Wollman, E. W.; Wrighton, M. S. Thh Solid Films 1992, 21Ol211, 341-347. Wang, J.; Naser, N.; Renschler, C. L. Anal. Lett. 1993,26,1333-1346. Kuhr, W. G.; Barrett, V. L.; Gagnon, M. R.; Hopper, P.; Pantano. P. Anal. Chem. 1993, 65, 617-622. Pantano, P.; Kuhr, W. G. Anal. Chem. 1993, 65, 623-630. Kawagoe, J. L.: Niehaus, D. E.; Wightman, R. M. Anal. Chem. 1991,

Strein, T. G.; Ewing, A. G. Anal. Chem. 1993, 65, 1203-1209. Lau, Y. Y.; Wong, D. K. Y.; Luo, G.; Ewing, A. G. Electroanalysis 1992, 4, 865-869. Huang, W.; McCreery, R. J. Electroanal. Chem. 1992, 326, 1-12. Wu, H. P. Anal. Chem. 1993, 65, 1643-1646. Shimizu, Y.; Morita, K. J. Electrochem. SOC. 1992, 139, 1240-1243. Li, W.; Virtanen, J. A,; Penner, R. M. J. Phys. Chem. 1992, 96, 6529- 6532.

913-924.

63, 2961-2965.

Brumlik, C. J.; Martin, C. R.; Tokuda, K. Anal. Chem. 1992, 64, 1201- 1203. Foss, C. A., Jr.; Hornyak, G. L.; Stockert. J. A,; Martin, C. R. J. Phys. Chem. 1992, 96, 7497-7499. Foss, C. A., Jr.; Tierney, M. J.; Martin, C. R. J. Phys. Chem. 1992, 96,

Klein, J. D.; Herrlck, R. D., 11; Palmer, D.; Sailor, M. J.; Brumiik, C. J.; Martin, C. R. Chem. Mater. 1993, 5, 902-904. Kounaves, S. P.; Deng, W. Anal. Chem. 1993, 65, 375-379. Krasinski, P.; Galus, 2. J. Elechoanal. Chem. 1993, 346, 135-146. Oldham, K. 8. J. Elechoanal. Chem. 1988, 250, I . Drew, S. M.; Wightman, R. M.; Amatore, C. A. J. Elechoanal. Chem.

Cooper, J. B.; Bond, A. M.; Oldham, K. B. J. Electroanal. Chem. 1992,

Lee, C.; Anson, F. C. J. Electroanal. Chem. 1992, 323, 381-389. Norton, J. D.; White, H. S. J. Elecfroanal. Chem. 1992, 325, 341-350. Cooper, J. B.; Bond, A. M. Anal. Chem. 1993, 65, 2724-2730. Norton, J. D.; Anderson, S. A.; White, H. S. J. Phys. Chem. 1992, 96,

Bento, M. F.; Medeiros, M. J.; Montenegro, M. I.; Beriot, C.; Pletcher, D. J. Elecfroanal. Chem. 1993, 345, 273-286. Ciszkowska, M.; Stojek, 2. J. Electroanal. Chem. 1993, 344, 135-143. Bard, A. J.; Garcia, E.; Kukharenko, S.; Strelets, V. V. Znorg. Chem.

Safford. L. K.; Weaver, M. J. J. Electroanal. Chem. 1992, 331, 857- 876. Wooster, T. T.; Longmire, M. L.; Zhang, H.; Watanabe, M.; Murray, R. W. Anal. Chem. 1992, 64, 1132-1140. Bond, A. M.; Pfund, V. B. J. Elechoanal. Chem. 1992, 335, 281-295. Vuki, M.; Kalaji, M.; Nyholm, L.; Peter, L. M. J. Electroanal. Chem. 1992, 332, 315-323. Golas, J.; Drickamer, H. G.; Faulkner, L. R. J. Phys. Chem. 1991, 95, 10191-10197. Golas, J.; Drlckamer, H. G.; Faulkner, L. R. Acta Chim. Hung. 1992, 129, 497-518. Dressman, S. F.; Garguilo, M. G.; Sullenberger, E. F.; Michael, A. C. J. Am. Chem. SOC. 1993, 175, 7541-7542. Ciszkowska, M.; Stojek, Z.; Morris, S. E.; Osteryoung, J. G. Anal. Chem

Morris, S. E.; Ciszkowska, M.; Osteryoung, J. G. J. Phys. Chem. 1993,

Feinberg, J. S.; Bowyer, W. J. Mlcrochem. J. 1993, 47, 72-78. Baldo, M. A.; Danieie, A.; Mazzocchin, G. A. Anal. Chlm. Acta 1993, 272, 151-159. Daniele, S.; Mazzocchin, G. A. Anal. Chim. Acta 1993, 273, 3-1 1. Gorski, W.; Cox, J. A. J. Elechoanal. Chem. 1992, 323, 163-178. Unwin, P. R.; Bard, A. J. Anal. Chem. 1992, 64, 113-119. Bowyer, W. J.; Clark, M. E.; Ingram, J. L. Anal. Chem. 1992, 64.459- 462. Wipf, D. 0.; Bard, A. J. Anal. Chem. 1992, 64, 1362-1367. Mirkin, M. V.; Fan, F.-R. F.; Bard, A. J. J. Electroanai. Chem. 1992,328, 47-62. Bard, A. J.; Mirkin, M. V.; Unwin, P. R.; Wipf, D. 0. J. Phys. Chem. 1992, 96, 1861-1868. Mirkin, M. V.; Richards, T. C.; Bard, A. J. J. Phys. Chem. 1993, 97, 7672-7677.

9001-9007.

1991, 317, 117-124.

331, 877-895.

3-6.

1993, 32, 3528-3531.

1992, 64, 2372-2377.

97, 10453-10457.

. . - . . . .

(879) Mirkin. M. V.; Buihhs, L. 0. S.; Bard, A. J. J. Am. Chem. SOC. 1993, 715. 201-204.

(B80) Zhou, F.; UnwhP. R.; Bard, A. J. J. Phys. Chem. 1992,96,4917-4924. (B81) Pierce, D. T.; Unwin, P. R.; Bard, A. J. Anal. Chem. 1992, 64, 1795-

1804. (882) Horrocks, 8. R.; Mirkin, M. V.; Pierce, D. T.; Bard, A. J.; Nagy, G.: Toth.

K. Anal. Chem. 1993, 65, 1213-1224. (883) Mirkin, M. V.; Arca, M.; Bard, A. J. J. Phys. Chem. 1993, 97, 10790-

10795. (884) Scott, E. R.; White, H. S.; Phipps, J. 8. Anal. Chem. 1993, 65, 1537-

1545. (B85) Frank, M. H. T.; DenuauR, G. J. Electroanal. Chem. 1993, 354, 331-

339. (B86) Kwak, J.; Anson, F. C. Anal. Chem. 1992, 64, 250-256. (887) Mirkin, M. V.; Fan, F. R.; Bard, A. J. Science 1992, 257, 364-369. (B88) Unwin, P. R.; Bard, A. J. J. Phys. Chem. 1992, 96, 5035-5045. (889) Ciolkowski, E. L.; Cooper, B. R.; Jankowski, J. A.; Jorgenson, J. W.;

Wightman, R. M. J. Am. Chem. SOC. 1992, 114, 2815-2821. (B90) Schroeder. T. J.; Jankowski, J. A.; Kawagoe, K. T.; Wightman, R. M.;

Lefrou, C.; Amatore, C. Anal. Chem. 1992, 64, 3077-3083. (B91) Chen, T. K.; Lau, Y. Y.: Wong, D. K. Y.; Ewing, A. G. Anal. Chem. 1992,

(892) Lau, Y. Y.; Abe, T.; Ewing, A. G. Anal. Chem. 1992, 64, 1702-1705. (893) Tanaka, K.; Kobayashi, F.; Isogai, Y.; Iizuka, T. Bioelechochem.

Bioenergetlcs 1991, 26, 413-421. (894) Matsue, T.; Koike, S.; Abe, T.; Itabashi, T.; Uchida. I. Biochim. Siophys.

Acta 1992, 1101, 69-72. (895) Malinski, T.; Taha. 2. Nature 1992, 358, 676-678. (896) Renner, K. J.; Pazos, L.; Adams, R. N. Brain Res. 1992, 577, 49-56. (897) Cammack, J.; Ghasemzadeh, B.; Adams. R. N. Brah Res. 1991, 565,

17-22. (B98) Ghosh, P. M.; Keese, C. R.; Glaever. I. Blophys. J. 1993, 64, 1602-

1609. (B99) Amatore, C.; Fosset, E.; Maness, K. M.; Wightman. R. M. Anal. Chem.

(8100) Morita, M.; Horluchi, T.; Tabei, H. J. Electroanal. Chem. 1992, 322, 191-201.

(8101) Niwa, 0.; Xu, Y.; Halsall, H. B.; Hieneman, W. R. Anal. Chem. 1993, 65, 1559-1563.

64, 1264-1268.

1993, 65, 2311-2316.


(8102) Horiuchi, T.; Niwa, 0.; Morka, M.; Tabei, H. Anal. Chem. 1992, 64,

(8103) Nishihara. H.; Dalton, F.; Murray, R. W. Anal. Chem. 1981, 63, 2955-

(8104) Nishizawa, M.; Sawaguchi, T.; Matsue, T.; Uchida, I. Synfh. Met. 1091,

(8105) Ju, H.; Chen, H.; Gao, H. J. flectroanal. Chem. I W 2 , 347, 35-46. (8106) Peng. W.; Wang. E. Anal. Chem. Wg3, 65, 2719-2723. (8107) Peng, W.; Li, P.; Zhou. X. J. flecfroanal. Chem. 1993, 347, 1-14. (8108) Coiiinson, M. M.; Wightman. R. M. Anal. Chem. 1993,65,2576-2562. (8109) Bartelt, J. E.; Drew, S. M.; Wightman, R. M. J. fktrochem. Soc. I W 2 ,

(8110) Verbrugge. M. W. J. fleckochem. SOC. 1892, 739, 3529-3535. (8111) Vleil, E. J. flectroanal. Chem. lggl , 378, 61-68. (8112) Verbrugge, M. W.; Baker, D. R. J. Phys. Chem. 1992, 96,4572-4560. (81 13) Bartlett, P. N.: Eastwick-Field, V. J. Chem. Soc., Faraday Trans. I W 3 ,

(8114) VHt, J. E.; Johnson, D. C.; Tailman, D. E. Anal. Chem. 1993, 65, 231-

(8115) Blauch, D. N.; Anson, F. C. J. Electroanal. Chem. 1989, 259, 1. (8116) Van der Linden, 8.; Vereecken, J. J. Electroanal. Chem. 1093, 356,

3206-3206.

2960.

45, 241-248.

739, 70-74.

89, 213-216.

237.

13-24. (8117) V k J . E.; Johnson, D. C. J. Electrochem. SOC. 1992, 739, 774-778. (8118) Engelhardt, G.; Schaepers, D.; Strehbiow, H.-H. J. Electrochem. SOC.

1092. 739. 2171-2175. (8119) Engelhardt; G.; Jabs, T.; Strehblow, H.-H. J. Electrochem. SOC. 1892,

(8120) Engeihardt, G.; Jabs, T.: Schaepers, D.; Strehbiow, H. H. Acta Chim.

(8121) Schwartz, D. T. J. Electrochem. SOC. 1993, 740, 452-458. (8122) Deslouis, C.; Triboilet, 8. flektrokhimiya 1993, 29, 84-88. (8123) Engeiman, E. E.; Evans, D. H. J. flecffoanal. Chem. 1993, 349, 141-

(8124) Kokkinidis, G.; Hasiotis, C.; Papanastasiou, G. J. Electroanal. Chem.

(8125) Chen, Y.; Zhang, H.; Wu, 8. J. Electroanel. Chem. 1992, 335,321-326. (8126) Lei, H.; Wu, 8.; Cha, C. J. flectroanal. Chem. 1992, 332, 257-264. (8127) Hofseth, C. S.; Chapman, T. W. J. flectrochem. SOC. 1902, 739,2525-

(8128) Baislev, H.; Britz, D. Acta Chem. Scand. 1992, 46, 949-955. (8129) Mount, A. R.; Appieton, M. S.; Albery, W. J.; Clark, D.; Hahn, C. E. W.

(8130) Jiang, R.; Anson, F. C. J. Phys. Chem. l W 2 , 96, 452-458. (8131) Van der Linden, 8.; De Keyzer, R.; Vereecken, J. J. flectroanal. Chem.

(8132) Aibery, W. J.; Clark, D.; Drummond, H. J. J.; Coombs, A. J. M.; Young,

(8133) Compton, R. G.; Brown, C. A. J. Colloid Interface Sci. 1993, 758,

(8134) Desiouis, C.; Ezzidi, A.; Triboiiet, 8. J. Appl. Electrochem. 1991, 27,

(8135) Gabrielli, C.; Huet, F.; Sahar, A.; Vaientln, 0. J. Appl. Electrochem.

(8136) Janssen, L. J. J. J. Appl. Electrochem. 1982, 22, 1091-1094. (8137) Krysa, J.; Wragg, A. A. J. Appl. flectrochem. 1892, 22, 429-436. (8138) Zdunek, A. D.; Seiman, J. R. J. Electrochem. SOC. 1992, 739, 2549-

2551. (8139) Yen, S.-C.; Wang, J.-S.; Chapman, T. W. J. flectrochem. SOC. 1992,

739, 2231-2238. (8140) Fisher, A. C.; Compton, R. 0.; Brett, C. M. A.; Oliveira-Brett, A. M. C.

F. J. flectroanal. Chem. 1091, 378, 53-59. (8141) Compton, R. G.; Fisher, A. C.; Latham, M. H.; Brett, C. M. A.; Oliveira-

Brett, A. M. C. F. J. Appl. Electrochem. 1092, 22, 1011-1016. (8142) Brett, C. M. A.; Oliveira Brett, A. M. C. F.; Fisher, A. C.; Compton, R.

G. J. flecffoanal. Chem. 1992, 334, 57-64. (8143) Compton, R. G.; Fisher, A. C.; Latham, M. H.; Brett, C. M. A,; Oiiveira-

Brett, A. M. C. F. J. Phys. Chem. 1992, 96, 8363-8367. (8144) Compton, R. G.; Fisher, A. C.; Latham, M. H.; Wellington, R. G.; Brett,

C. M. A.; Oliveira Brett, A. M. C. F. J. Appl. Electrochem. 1993, 23,

(8145) Compton, R. G.; Wellington, R. 0. Electroanalysis 1902, 4, 695-700. (8146) Compton, R. G.; Fisher, A. C.; Wellington, R. G.; Dobson, P. J.; Leigh,

(8147) TaA,R.J.;Burv,P.C.:Finnin,B.C.;Reed,B.L.;Bond,A.M.J.flectroanal.

739, 2176-2181.

Hung. 1992, 729, 551-556.

158.

1993, 350, 235-249.

2529.

J. flectroanal. Chem. 1992, 340, 287-300.

1993, 349, 311-324.

W. K.; Hahn, C. E. W. J. flecffoanal. Chem. 1992, 340, 99-110.

243-246.

1081-1066.

1992, 22, 801-809.

98-102.

P. A. J. Phys. Chem. 1993, 97, 10410-10415. . .

Chem. 1993,-356, 25-42. (8148) Compton, R. G.; Fisher, A. C. Electroana/ysis 1992, 4, 167-182. (8149) Chen, Q.: Wang, J.; Rayson, G.; Tian, 8.; Lin, Y. Anal. Chem. lW3 ,65 ,

251-254. (8150) FieMen, P. R.; McCreedy, T. Anal. Chim. Acta 1993, 273, 111-121. (8151) Stojanovic, R. S.; Bond, A. M.; Butler, E. C. V. flectroanalysis 1992,

(8152) Digua, K.; Kauffmann, J. N.; Ghanem, G.; Patriarche, G. J. J. Llq. Chromatogr. 1902, 75, 3295-3313.

(8153) Mattusch, J.; Weisch, T.: Werner, 0. J. Prakt. Chem. lgB2.334.49-52. (8154) Cooper, 8. R.; Jankowski, J. A.; Leszczyszyn, D. J.; Wightman, R. M.;

Jorgenson, J. W. Anal. Chem. 1992, 64, 691-694. (8155) Sloss, S.; Ewing, A. G. Anal. Chem. 1993, 65, 577-581. (8156) O'Shea, T. J.; Greenhagen, R. D.; Lunte, S. M.; Lunte, C. E.; Smyth,

M. R.; Radzik, D. M.; Watanabe, N. J. Chromatcgr. 1992, 593, 305- 312.

(8157) O'Shea, T. J.; Lunte, S. M. Anal. Chem. 1993. 65, 247-250. (8158) Lu, W.; Cassidy, R. M. Anal. Chem. 1993, 65, 1649-1653. (8159) Lu, W.; CassMy, R. M. Anal. Chem. 1983, 65, 2678-2881. (8160) Mahoney, L. A.; O'Dea, J.; Osteryoung, J. G. Anal. Chlm. Acta 1993,

4, 453-461.

267. 25-33.

(8161) TaA, R. J.; Bury, P. C.; Finnin, 8. C.; Reed, 8. L.; Bond, A. M. Anal. Chem. 1993. 65. 3252-3257. . -. -, . - . . -. - . -.

(8162) Sparks, T. C.; Geng, C. Anal. Bbchem. 1992, 205, 319-325. (8163) Aoki, A.; Matsue, T.: Uchida, I. Anal. Chem. 1092, 64, 44-49. (8164) Takahashi, M.; Mcflta, M.; Niwa, 0.; Tabei, H. J. flecffoanal. Chem.

(8165) Brown,G. N.; Birks, J. W.;Kovai.C.A. Anal. Chem. 1992.64,427-434. (8166) Wang. Y.; Yeung, E. S. Anal. Chlm. Acta 1092, 266, 295-300. (8167) Barisci, J. N.; Wallace, G. G. J. flecffoanal. Chem. 1892, 328, 195-

(8168) Dohertv, A. P.; Forster, R. J.; Smyth, M. R.; Vos. J. G. Anal. Chem.

1992, 335, 253-263.

208. . .

1992, 64, 572-575. (8169) Malone, 1259-1 263. M. M.; Dohem, A. P.; Smyth, M. R.; Vos, J. 0. Analyst 1992,

. - - - . - - -. (8170) Wang, J.; Wu, H.; Angnes, L. Anal. Chem. Wg3, 65, 1893-1696. (8171) Qalal, A.; AM, N. F.: Rubinson, J. F.; Zimmer, H.; Mark, H. 8.. Jr. Anal.

(8172) Wang. E.; Liu, A. Anal. Chlm. Acta 1091, 252, 53-57. (8173) Vandeberg, P. J.; Johnson, D. C. Anal. Chem. 1993, 65, 2713-2716. (8174) McLaughlin, L. G.; Henlon, J. D. J. Chromatogr. 1092, 59, 195-206. (8175) Wagner, H. P.; McGarrity, M. J. J. Am. Soc. Brew. Chem. 1992. 50,

(8176) Martens. D. A.: Frankenberaer, W. T., Jr. J. Lia. Chromatwra~hy 1992.

Lett 1993, 26, 1361-1381.

1-3. . .

75, 423-439. (8177) LaCourse. W. R.; Johnson, D. C. Anal. Chem. l W 3 , 65, 50-55. (8178) Vandeberg, P. J.; Kowagoe, J. L.; Johnson, D. C. Anal. Chlm. Acta . .

1982, 266, 1-11.

869-672. (8179) Soucaze-Gulllous, 8.: Kutner, W.; Kadish, K. M. Anal. Chem. 1993, 65,

- - - - . -. (8180) Luo, P.; Baldwin. R. P. Electroanalysis 1992, 4. 393-401. (8161) Salto, H.; Mural, S.: Abe, E.; Masuda, Y.; Itoh, T. Pharmacol. Biochem.

(8182) Zhu, C.; Curran, D. J. Electroanalysis WPl, 3, 511-518. (8183) Lu, J.; Tian, C. J. Elecfroanal. Chem. 1993, 345, 27-42.

C. ANALYTICAL VOLTAMMETRY

Behav. l W 2 , 42, 351-356.

(C1) (C2) (C3)

(C4)

(C5)

Barker. G. C.; Jenkins, I . L. Analyst 1992, 777, R1-R11. Barker, 0. C.; Gardner, A. W. Analyst 1992, 777. 1811-1828. Chin, K. Y.; Prasad, S.; O'Dea, J. J.; Osteryoung, J. Anal. Chim. Acta

Lovric, M.; Pizeta, I.; Komorskylovric, S. flecfroanalysis 1892, 4,

Komorskvlovric, S.; Lovric. M.; Branica. M. J. Electroanel. Cham. 1992.

1992, 264, 197-204.

327-337. . .

335, 29f-308. Kounaves, S. P. Anal. Chem. 1992, 64, 2998-3003. Brainina, K. 2.; Viichinskaya, E. A.; Khanina, R. M.; Kalnishevskaya, L. N. flectroanalyss I W 2 , 4, 549-554. Jin, W. R.; Hou, Y.C.; Yan, C. T.; Wang, J. Y.; Sun, C. L. Electroanalysis

(C6) (C7)

(C8) 1992. 4. 233-237.

. .

. - - -, . , - - . .

Li, C. A.; James, 8. D.; Magee, R. J. Electroanalysis 1992,4, 585-587. Puy, J.; Mas, F.; DlazCrur, J. M.; Esteban, M.; Casassas, E. Anal. Chlm. Acta 1982, 268, 261-274. Mas, F.; Puy, J.; DiazCruz, J. M.; Esteban, M.; Casassas, E. Anal. Chlm.

Puy, J.; Salvador, J.; Galceran, J.; Esteban, M.; Diaz-Cruz, J. M.; Mas, F. J. flectroanal. Chem. 1993. 360, 1-25. Jin. W. R.; Cui, H.; Wang, S. R. Anal. Chim. Acta 1992, 268,301-306. Sugawara, K.; Tanaka, S.; Taga, M. Fresenius J. Anal. Chem. 1892.

Aleixo. L. M.; Souza, M. D. 8.; Gcdinho, 0. E. S.; Neto, G. D.; Gushikem, Y.; Moreira, J. C. Anal. Chim. Acta I W 3 , 277, 143-148. Cai, X.; Kaicher. K.; Diewakl, W.; NeuhoM, C.; Magee, R. J. Fresenius J. Anal. Chem. 1993. 345, 25-31. Diewald, W.; Kalcher, K.; Neuhold, C.; Cai, X.; Magee, R. J. Anal. Chim. Acta 1993, 273, 237-244. Paniagua, A. R.; Vazquez, M. D.; Tascon, M. L.; Batanero, P. S. Electroanalysis 1993, 5, 155-163. Peng, T. 2.; Li, H. P.; Wang, S. W. Analyst l W 3 , 778, 1321-1324. Cai. X. H.: Kalcher, K.: Neuhoid. C.; Diewald. W.: Magee, R. J. Analvst

Acta 1993, 273, 297-304.

342, 65-69.

l W 3 , 778, 53-57. Egashira, N.; Iwanaga, H.; Okabe, K.; Ohga, K. Anal. Sci. 1882, 8, 71-15-707 . - - . - . . Ramos, J. A.; Bermejo, E.; Zapardiei, A.; Perez, J. A.; Hernandez, L. Anal. Chlm. Acta 1993, 273, 219-227. Aivarez, E.; Sevilla, M. T.; Piniila, J. M.; Hernandez, L. Anal. Chlm. Acta

Macias, J. M. P.; Hernandez, L. H.; Sobrino, J. M. M.; Escribano, M. T. S. Electfoanalysls 1993, 5, 79-63. Barrio. R. J.: Debaluaera. 2. G.: Goicolea. M. A. Anal. Chim. Acta 1993.

1992, 260. 19-23.

- 273, 93-99. Hernandez, P.; Garcia, S.; Hernandez, L. Anal. Chlm. Acta 1992, 259, 325-331. Cookeas. E. 0.; Efstathiou, C. E. Analyst 1902. 777, 1329-1334. Liu, K. 2.; Wu, Q. G. flecfroanalysls 1992, 4, 569-573. Gorski, W.; Cox, J. A. Anal. Chem. 1992, 64, 2706-2710. Turyan, I.; Mandler, D. Anal. Chem. 1893, 65, 2089-2092. Sun. c. G.: Wana, J. Y.; Hu, W.; Xie. T. Y.; Jin, W. R. Anal. Chim. Acta 1992, 259, 319-323. Zhao, J. 2.; Sun, D. 2.; Jin, W. R. Anal. Chim. Acta 1092,268,293-299. Wang, J.; Lu, J. M.; Setiadjl, R. Tabnta 1903, 40, 351-354. Wang, J.; Setiadji, R. Anal. Chlm. Acta 1982, 264, 205-211. Farias. P. A. M.: Takase. I . flectroanalvsis W92. 4. 823-828. Stryjewska, E.; Rubel. S.f Kusmierczyk, U. Chem. Anal. 1992, 37,43- 49.


Ertas, F. N.; Fogg, A. G.; Moreira, J. C.; Barek, J. Talanta 1993, 40, I AR 1- l 4 R R . . - . . . - - . Fogg, A. G.; Ertas, F. N.; Moreira, J. C.; Barek, J. Anal. Chim. Acta 1993. 278. 41-51. Quentel, F.'; Elleouet, C.; Madec, C. Electroanalysis 1992, 4, 707-71 1. Viliar, J. C. C ; Garcia, A. C.; Blanco, P. T Anal. Chim. Acta 1992, 256,

Debozo, J. A.; Garcia, A. C.; Ordieres, A. J. M.; Blanco, P. T. 23 1-236.

€lectroanalysis 1992, 4, 87-92. Malone, M. A.; Garcia, A. C.; Blanco, P. T.; Smyth, M. R. Analyst 1993, 118. 649-655. . , . . . . . Deipozo, J. A.; Garcia, A. C.; Blanco, P. T. Anal. Chim. Acta 1993, 273, 101-109. Bermejo, E.; Zapardiel, A,; Perez, J. A.; Huerta. A,; Hernandez, L. Talanta 1993, 40, 1649-1656. ARlnoz, S.; Ozer, D.; Temizer, A,; Bayraktar, Y. Anal. Lett. 1992, 25, 11 1-118. Wang. 2. H.; Zhou, H. X.; Zhou, S. P. Talanta 1993, 40, 1073-1075. Peng, T. 2.; Li, H. P.; Lu, R. S. Electroanalysis 1993, 5, 177-181. Hu, S. S.; Chen, 2. L.; Zhang, T. Fresenius J. Anal. Chem. 1993, 346, 1008- 10 10. Villamii, M. J. F.; Ordieres, A. J. M.; Garcia, A. C.; Blanco, P. T. Anal. Chim. Acta 1993, 273, 377-382. Economou, A.; Fielden, P. R. Analyst 1993, 778, 47-51. Economou, A.; Fielden, P. R. Analyst 1993, 778, 1399-1404. Komorsky-Lovric, S.; Lovric, M.; Bond, A. M. Anal. Chim. Acta 1992,

Schoiz, F.; Rabi, F.; Muller, W. D. €lectroanalysis 1992, 4, 339-346. Lange, B.; Scholz, F.; Bautsch. H. J.; Damaschun, F.; Wappier, G. Phys. Chem. Miner. 1993, 79, 486-491. Zhi. W.; Galai, A.; Zimmer, H.; Mark, H. 8. Electroanalysis 1992, 4, 77-85. Wallace, G. G.; Imisides, M. D. Electroanalysis 1992, 4, 97-105. Wang, J.; Brennsteiner, A,; Angnes, L.; Sylwester, A,; Lagasse, R. R.; Bitsch, N. Anal. Chem. 1992, 64, 151-155. Wang, J.; Angnes, L.; Tobias, H.; Roesner, R. A,; Hong, K. C.; Glass, R. S.: Kong, F. M.; Pekala, R. W. Anal. Chem. 1993, 65, 2300-2303. Wang, J.; Tian, B. M. Anal. Chem. 1992, 64, 1706-1709. Frenzel, W. Anal. Chim. Acta 1993, 273, 123-137. Peng, J. X.; Jin, W. R. Anal. Chim. Acta 1992, 264, 213-219. Rievaj, M.; Bustin, D. Analyst 1992, 777, 1471-1472. Rievaj, M.; Mesaros, S.; Bustin, D. An. Quim. 1993, 89, 347-350. Rievaj, M.; Mesaros, S.; Bustin, D. Chem. Pap-Chem. Zvesti. 1993, 47, 31-33. McLaughlin, K.; Boyd, D.; Hua, C.; Smyth, M. R. Electroanalysis 1992, 4, 689-693. Nyholm, L.; Wikmark, G. Anal. Chim. Acta 1993, 273, 41-51. Daniele. S.; Mazzocchin, G. A. Anal. Chim. Acta 1993, 273, 3-1 1, Kounaves, S. P.; Deng, W. Anal. Chem. 1993, 65, 375-379. Opydo, J. Talanta 1992, 39, 229-234. Cofre, P.; Brinck, K. Talanfa 1992, 39, 127-136. Opydo, J. Anal. Chim. Acta 1992, 262, 117-122. Barisci, J. N.; Wallace, G. G. Electroanalysis 1992, 4, 323-326. Daniel, L. Y.; Zakharova, E. A,; Goloskokova, N. B.; Shelkovnikov, V. V. Zh. Anal. Khim. 1992, 47, 448-455. Fernando, A. R.; Plambeck, J. A. Analyst 1992, 7 77, 39-42. Diaz-Cruz, J. M.; Esteban, M.; van den Hoop, M. A. G. T.; van Leeuwen, H. P. Anal. Chem. 1992, 64, 1769-1776. Saito, S.; Osteryoung, J. Anal. Chim. Acta 1992, 258, 289-297. Peng, T. H.; Li, H. P.; Lu, R. S. Anal. Chim. Acta 1992, 257, 15-19. Mikac, N.; Branica, M. Anal. Chim. Acta 1992, 264, 249-258. Voulgaropoulos, A.; Tzivanakis, N. Electroanalysis 1992, 4, 647-65 1. Wong, G. T. F.; Zhang, L. S. Talanta 1992, 39, 355-360. Vonwandruszka, R.; Yuan, X.; Morra, M. J. Talanta 1993, 40, 37-42. Wang, J.; Lu, J. M. Anal. Chim. Acta 1993, 274, 219-224. McLaughlin, K.; Rodriguez, J. R. B.; Garcia, A. C.; Blanco, P. T.; Smyth, M. R. Electroanalysis 1993, 5, 455-460. Smyth, W. F.; Jan, M. R. Fresenius J. Anal. Chem. 1993,346,947-95 1. Kotoucek, M.; Vasicova, J.; Ruzicka, J. Mlkrochim. Acta 1993, 7 7 7 , 55-62. Jin, W. R.: Zhao, X.; Du, Q. L.; Wana F. N.; Gao, 2. Q. Anal. Lett. 1992,

258, 299-305.

25, 2209-2223. Ciszewski, A.; Wang, J. Analyst 1992, 777, 985-988. Zanoni, M. V. B.; Fogg, A. G. Analyst 1993, 778, 1163-1166. Legall, A. C.; van den Berg, C. M. G. Analysf 1993, 778, 1411-1415. Kuver. A.: Vielstich. W.: Kltzelmann. D. J. Electroanal. Chem. 1993. , . 353, 255-263.~ Wang, J.; Tian, B. Anal. Chem. 1993, 65, 1529-1532. Zie, Y . Q.; Huber, C. 0. Anal. Chim. Acta 1992, 263, 63-70. Ostapczuk, P. Clin. Chem. 1992, 38, 1995-2001. Jagner, D.; Sahlin, E.; Axelsson. B.; Ratanaohpas, R. Anal. Chim. Acta 1993, 278, 237-242. Zhang, Y. L.; Jiao, K.; Liu, C. F.; Liu, X. B. Anal. Chim. Acta 1993, 282, 125-132. Komorsky-Lovric, S.; Branica, M. Anal. Chim. Acta 1993, 276, 361- 366. Aldstadt, J. H.; Dewald, H. D. Anal. Chem. 1993, 65, 922-926. Wang, J.; Lu, J. M.; Olsen, K. Analyst 1992, 777, 1913-1917. Jiao, K.; Jin, W.; Metzner. H. Anal. Chim. Acta 1992, 260, 35-43. Setiadji, R.; Wang, J.; Santanarios, G. Talanta 1993, 40, 845-849. Wang, J.; Lu, J. M.; Taha. 2. Analyst 1992, 177, 35-37. Yokoi, K.; van den Berg, C. M. G. Anal. Chim. Acta 1992, 257, 293-

Yokoi, K.; van den Berg, C. M. G. Electroanalysis 1992, 4. 65-69. Bobrowski, A.; Bond, A. M. Electroanalysis 1992, 4, 975-979. Hsieh, A. K.; Ong, T. H. Anal. Chim. Acta 1992, 256, 237-241.

299.

(C106) Jiang, 2. L.; Qin, H. C.; Wu, D. Q. Talanra 1992, 39, 1239-1244. (C107) Chan, W. H.; Lee, A. W. M.; Cai, P. X. Analyst 1992, 777, 185-188. (C108) Chan, W. H.; Lee, A. W. M.; Cal, P. X. Analyst1992. 777, 1509-1512. (C109) Chan, W. H.; Lee, A. W. M.; Ng, S. L.; Liu, W. L. Analyst 1992, 777,

(Cl lO) Shiu, K. K.; Chan. W. H.; Lee, A. W.; Wong, W. C. Analyst 1993, 778,

(C111) Rodrigues, J. A.; Barros, A. A. Anal. Chim. Acta 1993, 273, 531-537. (C112) Barros, A. A.; Rodrigues, J. A.; Almeida, P. J. Anal. Chim. Acta 1993,

(C113) Somer, G.; Kocak, A. Analyst 1993, 778, 657-659. (C114) Harbin, A. M.; van den Berg, C. M. G. Anal. Chem. 1993, 65, 3411-

(C115) Lyle, S. J.; Yassin, S. S. Anal. Chim. Acta 1993, 274, 225-230. (C116) Reviejo, A. J.; Sampron. A.; Pingarron, J. M.; Polo, L. M. Elechosnalysis

1909-19 12.

869-872.

273, 539-543.

3416.

1992. 4. 11 1-120. , (C117) Reviejo, A. J.; &nzalez, A,; Pingarron, J. M.; Polo, L. M. Anal. Chim.

Acta 1992. 264. 141-147. (C l l8 ) Gaivez, R.: Pedrero, M.; Devillena, F. J. M.; Pingarron, J. M.; Polo, L.

(C119) Acuna, J. A.; de la Fuente, C.; Vazquez, M. D.; Tascon, M. L.; Sanchez-

(C120) Garcia-Antbn, J.; Grima, R. Fresenius J. Anal. Chem. 1992, 343,905-

(C121) Ciszkowska. M.; Stojek. 2.; Morris, S. E.; Osteryoung, J. G. Anal. Chem.

(C122) Morris, S. E.; Ciszkowska, M.; Osteryoung. J. G. J. Phys. Chem. 1993,

M. Anal. Chim. Acta 1993, 273, 343-349.

Batanero, P. Talanta 1993, 40, 1637-1642.

906.

1992, 64, 2372-2377.

97. 10453-10457 . ... . .

(C123) Baido, M. A.; Daniele, S.; Mazzocchin, G. A. Anal. Chim. Acta 1993, 272. 151-159. ~ ~. ~

(C124) Perdicakis, M.; Piatnicki, C.; Sadik, M.; Pasturaud, R.; Benzakour, B.;

(C125) Kuiesza, P. J.; Faulkner, L. R. J. Am. Chem. Soc. 1993, 775, 11878-

(C126) Batina, N.; Ciglenecki. I.; Cosovic, B. Anal. Chlm. Acta 1992, 267,

(C127) Diaz, T. G.; Cabaniilas, A. G.; Martinez, L. L.; Salinas, F. Anal. Chlm.

(C128) Sturm, J. C.; Nunezvergara. L. J.; Squella, J. A. Talanta 1992, 39,

(C129) Corbini, G.; Biondi, C.; Proietti, D.; Dreassi, E.; Corti, P. Analyst 1993,

((2130) Szczepaniak, W.; Ren, M. Anal. Chim. Acta 1993, 273, 335-338. (C131) Szczepaniak, W.; Ren, M. Anal. Chim. Acta 1993, 273, 339-342. (C132) Boutakhrit, K.: Elkasmi. A.; Kauffmann, J. M.; Deltour, R.; Mehbod, M.;

(C133) Lafage, B.; Taxil, P. J. Electrochem. Soc. 1993, 740, 3089-3093. (C134) Rammohan, V.; Yadav, R. B.; Ramamurty, C. K.; Syamsundar, S. Anal.

(C135) Dempsey, E.; Smyth. M. R.; Richardson, D. H. S. Analyst 1992, 777,

(C136) Ni, Y. N.; Selby, M.; Kokot, S.; Hodgkinson, M. Analyst 1993, 778,

('2137) Matysik, F. M.; Nagy, G.; Pungor, E. Anal. Chim. Acta 1992, 264, 177-

Bessiere, J. Anal. Chim. Acta 1993, 273, 81-91.

11884.

157- 164.

Acta 1993, 273, 351-359.

1149-1 154.

718, 183-187.

Marvin, C. A. Electroanalysis 1993, 5, 877-882.

Chim. Acta 1992, 264, 149-152.

1467-1470.

1049-1053.

184. - .

(C138) Engbiom, S.; Bobacka, J.; Ivaska, A.; Nagy. G.; Sarkany, P.; Pungor,

(C139) Dos Santos, M. M. C.; Goncalves, M. L. S. Electrochim. Acta 1992, 37, E. Talanta 1992, 39, 819-824.

14 13- 141 6. (C140) Wikiel, K.; dos Santos, M. M.; Osteryoung, J. Electrochim. Acta 1993,

(C141) Iyer, V. N.; Sarin, R. Anal. Lett 1992, 25, 1915-1927. (C142) Bianchi, A.; Domenech, A.; Garcia Espana, E.; Luis, S. V. Anal. Chem.

(C143) Esteban, M.; Diaz-Cruz, J. M. Anal. Chim. Acta 1993, 287, 271-280. (C144) Zelic, M.; Branica, M. Anal. Chim. Acta 1992, 268, 275-284. (C145) Van den Berg, C. M. G.; Donat, J. R. Anal. Chim. Acta 1992, 257,

(C146) Van den Berg, C. M. G. Analyst 1992, 777, 589-593. (C147) Navratiiova, 2.; Kula, P. Anal. Chim. Acta 1993, 273, 305-311. (C148) Chakrabarti. C. L.; Lu, Y. J.; Cheng, J. G.; Back, M. H.; Schroeder, W.

(C149) Agraz, R.; Sevilla, M. T.; Hernandez, L. Anal. Chim. Acta 1993, 283,

(C150) Scarano. G.; Bramanti, E.; Zirlno, A. Anal. Chim. Acta 1992, 264, 153-

(C151) Fukushima, M.; Hasebe, K.; Taga, M. Anal. Chim. Acta 1992, 270,

(C152) Allus, M. A.; Brereton, R. G. Analyst 1992, 777, 1075-1084. (C153) Ni. Y. N.; Kokot, S.; Selby, M.; Hodgkinson, M. Electroanalysis 1992,

(C154) Esteban, M.; Ruisanchez, 1.; Larrechi, M. S.; Rius, F. X. Anal. Chim.

(C155) Esteban. M.; Ruisanchez, I.; Larrechi, M. S.; Rius, F. X. Anal. Chim.

38, 1555-1558.

1993, 65, 3137-3142.

281-291.

H. Anal. Chim. Acta 1993, 276, 47-64.

650-656.

162.

153-159.

4, 713-718.

Acta 1992, 268, 95-105.

Acta 1992, 268, 107-114.

D. HETEROGENEOUS/HOMOGENEOUS KINETICS

(Dl) (D2) (D3)

(D4) (05)

Fawcett, W. R.; Opallo, M. J. Phys. Chem. 1992, 96, 2920-2924. Fawcett, W. R.; Opallo, M. J. Electroanal. Chem. 1993, 349, 273-284. Phelps, D. K.; Ramm, M. T.; Wang. Y .; Nelsen, S. F.; Weaver, M. J. J. Phys. Chem. 1993, 97, 181-188. Fawcett. W. R.; Fedurco, M. J. Phys. Chem. 1993, 97, 7075-7080. Fawcett, W. R.; Fedurco, M.; Opallo, M. J. Phys. Chem. 1992, 96, 9959-9964.

414R Analytical Chemistry, Voi. 66, No. 12, June 15, 1994

Cruanes, M. T.; Drickamer, H. G.; Fauikner, L. R. J. Phys. Chem. 1992,

Fawcett, W. R.; Opailo, M.; Fedurco, M.; Lee, J. W. J. Electroanel. Chem. 1993, 344, 375-381. McDermott, C. A.; Kneten, K. R.; McCreery, R. L. J. Electrochem. SOC.

Straus, J. 6.; Voth, 0. A. J. Phys. Chem. 1993, 97, 7388-7391. Berhan, J.; Geilardo, I . ; Moreno, M.; Saveant, J. M. J. Am. Chem. SOC.

96, 9888-9892.

1993, 740, 2593-2599.

1992, 7 74. 9576-9583. Saveant, J. M. J. Am. Chem. SOC. 1992, 774, 10595-10602. Andrieux, C. P.; Legorande, A.; Saveant. J. M. J. Am. Chem. Soc. 1992. 7 74. 6892-6904. Jaworski,J. S.; Leszczynski, P.; Kaiinowski. M. K. J. Electroanal. Chem. 1993, 358, 203-219. Cariln, R. T.; Sullivan, T.; Sherman, J. W.; Aspinwali, C. A. Electrochim. Acta 1993, 38, 927-934. Karpinski, 2. J.; Osteryoung, R. A. J. Elechoanal. Chem. 1993, 349,

Safford, L. K.; Weaver, M. J. J. Electroanal. Chem. 1992, 337, 857- 876. Lavagnlni, 1.; Pastore, P.; Magno, F. J. Electroanal. Chem. 1992, 333, 1-10. Birke, R. L.; Huang, 2. P. Anal. Chem. 1992, 64, 1513-1520. Mirkln. M. V.; Bard, A. J. Anal. Chem. 1992, 64, 2293-2302. Klm, M. H.; Smkh, V. P.; Hong, T. K. J. Electrochem. SOC. 1993, 740,

Munoz, E.; Rodriguez Amaro, R.; Camacho, L.; Lopez, V. J. Electroanal. Chem. 1992, 333, 153-164. Engstrom, R. C.; Small, B.; Kattan, L. Anal. Chem. 1992,134,241-244, Cassldy, J.; Breen. W.; McGee, A.; McCormacx, T.; Lyons, M. E. G. J. Electroanel. Chem. 1992, 333, 313-318. Mirkin, M. V.; Rlchards, T. C.; Bard, A. J. J. Phys. Chem. 1993, 97, 7673-7677

285-297.

712-721.

. - .- . - . . . Andrieux, C. P.; Delgado, G.; Saveant, J. M.; Su, K. B. J. Electroanel. Chem. 1993, 348, 107-121. Smith, C. P.; White, H. S. Anal. Chem. 1993, 65, 3343-3353. Eichhorn, E.; Rieker, A.; Spelser, B. Anal. Chlm. Acta 1992, 256, 243- 249. Hsueh, C. C.; Brajter-Toth, A. Anal. Chem. 1993, 85, 1570-1575. Bieniasz, L. K. J. Electroanel. Chem. 1993, 360, 119-138. Horno, J.; Garcla Hernandez, M. T.; Gonzaiez Fernandez, C. F. J. Electroanal. Chem. 1993, 352, 83-97. Rudolph, M.. J. Electroanal. Chem. 1992, 338, 85-98. Brltz, D. J. Electroanal. Chem. 1993, 352, 17-28. Storzbach, M.; Helnze, J. J. Electroanal. Chem. 1993, 346, 1-27. Bieniasz, L. K.; Britz, D. Anal. Chim. Acta 1993. 278, 59-70. BbniaSZ, L. K.; Britz, D. Acta Chem. Scand. 1993, 47, 757-767. Bieniasz, L. K. J. Elechoanal. Chem. 1993, 345, 13-25. Mirkin. M. V.; Bard, A. J. J. Electroanal. Chem. 1992, 323, 1-27. Mirkin, M. V.; Bard, A. J. J. Electroanal. Chem. 1992, 323. 29-51. Zhou, F. M.; Unwin, P. R.; Bard, A. J. J. Phys. Chem. 1992, 96, 4917- 4924. Dong, S. J.; Che, G. L. Electrochim. Acta 1992, 37, 2587-2589. Che, 0. L.; Dong, S. J. Electrochim. Acta 1992, 37, 2695-2699. Che, 0. L.; Dong, S. J. Electrochlm. Acts 1992, 37, 2701-2705. Lavagnini, I.; Pastore, P.; Magno. F. J. Electroanal. Chem. 1993, 358,

Evans, D. H. J. Electroanal. Chem. 1992, 324, 387-395. Andrieux, C. P.; Haplot. P.; Saveant, J. M. J. Electroanel. Chem. 1993,

Maestre, M. S.; Munoz, E.; Avila, J. L.; Camacho, L. Electrochim. Act8 1992, 37, 1129-1 134. Meiiado, J. M. R.; Montoya, M. R.; Gaivin, R. M. Electroanalysis 1992.

Laviron, E.; Meunier-Prest, R. J. Electroanal. Chem. 1992, 324, 1-18. Vincent, M. L.; Peters, D. G. J. Electroanel. Chem. 1993, 344, 25-44. Kumar, V. T.; Blrke, R. L. Anal. Chem. 1993, 65, 2428-2436. Bieniasz, L. K. Comput. Chem. 1993, 77, 355-368. Bbniasz, L. K. J. Electroanal. Chem. 1992, 340, 19-34. Palvs. M. J.: 60s. M.; van der Linden, W. E. Anal. Chlm. Acta 1993,283,

193-201.

349, 299-309.

4, 217-221.

. . 81 i-829.

(D54) Compton, R. G.; Wellington, R. G. Electroanalysis 1992, 4, 695-700. (D55) Fisher, A. C.; Compton, R. G. Electroanalysis 1992, 4, 311-315. (D56) Compton, R. G.; Fisher, A. C.; Spackman, R. A. Electroanalysls 1992,

(D57) Compton, R. G.; Fisher, A. C.; Latham, M. H.; Wellington, R. G.; Brett, C. M. A.; Brett, A. M. C. F. 0. J. Appl. Electrochem. 1993,23,98-102.

(D58) Benderskii, Y. V.; Malranovskii, V. 0. Elektrokhimlye 1992, 28, 835- 841.

(D59) Daasbjerg, K. Acta Chem. Scad. 1993. 47, 398-402. (D60) Murphy, W. D.; Manzanares, J. A.; Mafe, S.; Relss, H. J. Phys. Chem.

(D61) Karasevskii. A. I.: Krls. R. E.: Panov, E. V.: Gorodvskii. A. V. J. Electrasnal.

4, 167-182.

1992, 96, 9983-9991, . .

Chem. 1992. 325, 45-63. (D62) Damaskin, 8. 6.; Safonov, V. A. J. Electroanel. Chem. 1992, 329,

139-1 58. (D63) IzotOviV. Y.; Kuznetsov, A. M. Elektfokhlmly8 1992,28, 1109-1117. (D64) Hsu, J. P.; KUO, Y. C. J. Chem. Soc., Faraday Trans. 1993. 89, 1229-

1233. (D65) Daghetti, A.; Romeo, S.; Usueiii. M.; Trasatti, S. J. Chem. Soc., Faraday

Trans. 1993, 89, 187-193. (D66) Hamelin, A.; Foresti, M. L.; Guidelii, R. J. Electroanal. Chem. 1993,346,

(D67) Fawcett, W. R.; Rocha, R. C. J. Chem. Soc., Faraday Trans. 1992, 86, 1 143-1 148.

251-259.

(D68) Fawcett, W. R.; Kovacova, 2.; Motheo. A. J.; Foss, C. A. J. Electroanal. . . Chem. 1992, 326, 91-103.

(D69) Wandlowski, T.; DeLevie, R. J. Electroanel. Chem. 1992, 329, 103- 127. Wandlowski, T.; DeLevie, R. J. Electroanal. Chem. 1993, 345, 413- 432. Wandlowski, T.; DeLevie, R. J. Electroanal. Chem. 1993, 352, 279- 294. Swietiow, A.; Skoog, M.; Johansson, 0. Electroana&sls 1992,4,921- 928. Conway, B. E.; Liu, J. 6.; Qian, S. Y. J. Electroanel. Chem. 1992, 329. 201-223. Bagotskaya, I . A.; Kazarlnov, V. E. J. Electroanal. Chem. 1992, 329,

Perez, M.; Barrera. M.; Andreu, R.; Moiero, M. J. Electroanal. Chem.

Bai, L.; Gao, L.; Conway, B. E. J. Chem. SOC., Faraday Trans. 1993.

Jaworski, R. K.; McCreery, R. L. J. Electrochem. Soc. 1993, 740,1360- 1365. Halsey, T. C.; Leibig, M. Ann. Phys. (MY.) 1992, 279, 109-147. Leibig, M.; Halsey, T. C. Electrochim. Acta 1993, 38, 1985-1988. Unwin, P. R.; Bard, A. J. Anal. Chem. 1992, 64, 113-119. Unwin. P. R.; Bard, A. J. J. Phys. Chem. 1992, 96, 5035-5045. Papadopoulos. N.; Sotiropoulos, S.; Nikitas. P. J. Electroanal. Chem.

Gu, P.; Bai, L.; Gao, L.; Brousseau, R.; Conway, B. E. Electrochlm. Acta

Blankenborg, S. G. J.; Sluyters-Rehbach, M.; Sluyters, J. H. J. Electroanal. Chem. 1993, 349, 255-272. Avaca, L. A.; Kaufmann, S.; Kontturi, K.; Mwtomaki, L.; Schlffrin, D. J. Ber. Bunsenges. Phys. Chem. 1993, 97, 70-76. Tilak, B. V.; Conway, B. E. Electrochim. Acta 1992, 37, 51-61. Song, S. Y.; Jin, W. R.; Wang, S. R.; He, P. X. J. Electroanel. Chem.

225-236.

1993, 367, 239-249.

89, 235-242.

1992. 324, 375-385.

1992, 37, 2145-2154.

1992. 338. 61-72. . . - -. . - -, . . . -.

(D88) Jin, W. R.; Song, S. Y.; Wang, S. R.; He, P. X. J. Electroanel. Chem.

(D89) Jin. W. R.; Cui. H.; Zhu, L. X.; Wang, S. R. J. Elechoanal. Chem. 1992, 340. 315-324.

1992, 338, 73-84.

(D90) O'Dea, J. J.; Ribes, A.; Osteryoung, J. G. J. Electroanal. Chem. 1993,

(D91) ODea, J. J.; Osteryoung, J. G. Anal. Chem. 1993, 65. 3090-3097. (D92) Rouquette Sanchez, S.; Picard, G. Electrochim. Acta 1993, 38, 487-

493. (D93) McDermott. M. T.; Kneten, K.; McCreew, R. L. J. Phys. Chem. 1992,

345, 287-30 1.

96, 3124-3130. (D94) Engelman, E. E.; Evans, D. H. J. Electroanal. Chem. 1992, 337, 739-

749 (D95) Schulz, C.; Speiser, 8. J. Electroanel. Chem. 1993, 354, 255-271. (D96) Lukaszewski, 2.; Tomaszewski, K.; Mendyk, W. J. Electroanel. Chem.

(D97) Freund, M. S.; Brajter-Toth, A. J. Phys. Chem. 1992, 96, 9400-9406. (D98) Dana, S. M.; Jablonski, M. E.; Anderson, M. R. Anal. Chem. 1993, 65,

1 120-1 122.

1993, 344, 13-24.

E. SURFACE ELECTROCHEMISTRY

(El) Leiva, E. P. M. Chem. Phys. Lett. 1991, 787, 143-148. (E2) Trasatti, S. J. Electroanel. Chem. 1992, 329, 237-246. (E3) Wandlowski. T.; de Levie, R. J. Elechoanal. Chem. 1993, 352, 279-

294. (E4) Schrettenbrunner, M.; Chaiyasith, P.; Baumg&el, H. Ber. Bunsenges.

Phys. Chem. 1993, 97, 843-847, 847-459. (E5) Nikitas, P. J. Electroanel. Chem. 1993, 348, 59-80. (€6) Kurtyka, 8.; Kalsheva, M.; de Levie, R. J. Electroanal. Chem. 1992,347,

(€7) De Levle, R.; Vogt, A. J. Electroanel. Chem. 1992, 347, 353-360. (E%) Nikltas, P. J. Electroanal. Chem. 1991, 376, 23-35. (E91 Nikitas, P.; Anastopoulos, A.; Papanastasiou, G. J. Electroanal. Chem.

1991, 377, 43-76. (E10) Nlkitas, P. Electrochlm. Acta 1993, 38, 1441-1451. (E l l ) Nikitas, P. Electrochlm. Acta 1992, 37, 81-90. (€12) Nikitas. P. Langmulr 1993, 9, 2737-2747. (€13) Nikitas. P. Electrochlm. Acta 1992, 37, 1919-1925. (E14) Matsul,T.; Jorwnsen, W.L. J.Am. Chem. Soc. 1992, 774,3220-3226. (E15) Marshall, S. L.; Conway, B. E. J. Electroanel. Chem. 1992, 337, 19-43,

(E16) Tilak. B. V.;Chen, C.-P.; Rangarajan, S. K. J. Electroanel. Chem. 1992,

(E171 Diard, J.-P.; Le Gorrec, B.; Montella, C.; Montero-Ocampo, C. J. Ebctroanal. Chem. 1993, 352, 1-15.

(€18) Harrington, D. A. J. Electroanel. Chem. 1993, 355, 21-35. (E19) Scott, K. J. Electroanel. Chem. 1992, 325, 1-22. (E20) Tilak, B. V.; Conway. B. E. Electrochim. Acta 1992, 37, 51-61. (E21) Mlshra, A. K.; Bhattacharjee, 6.; Rangarajan, S. K. J. Elecbpanal. Chem.

1992, 337, 801-813. (E22) Rouquette, S.; Picard, 0. Electrochlm. Acta 1993, 38. 487-493. (E23) O'Dea, J. J.; Osteryoung, J. 0. Anal. Chem. 1993, 65, 3090-3097. (E241 O'Dea. J. J.; Ribes, A.; Osteryoung, J. G. J. Elechoanal. Chem. 1993.

345, 287-301. (E251 Reeves, J. H.; Song, S.; Bowden, E. F. Anal. Chem. 1993.65,683-688. (€26) Lovric, M.; Komorsky-Lovric, S.; Bond, A. M. J. Electroanal. Chem.

1991, 379, 1-18. (E27) Jaworskl, A.; Stojek, 2.; Scholz, F. J. Electroanal. Chem. 1993, 354,

1-9.

343-35 1.

45-66.

324. 405-414.


Lovric, M.; Pizeta, I.; Komorsky-Lovric, S. Electroanalysis 1992, 4,

Freund, M. S.; BraJter-Toth, A. J. Phys. Chem. 1992, 96, 9400-9406. Dana. S. M.: Jablonski. M. E.: Anderson, M. R. Anal. Chem. 1993, 65,

327-337.

1120-1122. Kano, K.; Uno, B. Anal. Chem. 1993, 65, 1088-1093. Schulz, C.; Spelser, B. J. Electroanal. Chem. 1993, 354, 255-271. Leverenz, A.; Speiser, B. J. Electroanal. Chem. 1991, 378, 69-89. Song, S.; Jln, W.; Wang, S.; He, P. J. Electroanal. Chem. 1992, 338, 61-72. Jin, W.; Song, S.; Wang, S.; He, P. J. Electroanal. Chem. 1992, 338, 73-84. Jin. W.; Cui, H.; Wang, S. Anal. Chim. Acta 1992, 268, 301-306. Engelman, E. E.; Evans, D. H. J. Elechoanal. Cbem. 1992, 337, 739- 749. Molina, A.; Lopez-Tenes. M.; Serna, C.; Albaladejo, J. Bull. SOC. Chim. Belg. 1991, 700, 703-716. Rouquette-Sanchez, S.; Picard, G. Electrochim. Acta 1993, 38, 487- 493. Verbrugge, M. W.; Baker, D. R.; Newman, J. Elechochlm. Acta 1993, 38, 1649-1859. Leibig, M.; Halsey, T. C. J. Electroanal. Chem. 1993, 358, 77-109. Zalis, S.; Posplsil, L.; Fanelli, N. J. Electroanal. Chem. 1993, 349, 443- 452. OCOn, P.; Herrasti, P.; Vazquez, L.; Salvarezza, R. C.; Vara. J. M.; ANia, A. J. J. Electroanal. Chem. 1991, 379, 101-110. Louch, D. S.; Pritzker, M. D. J. Electroanal. Chem. 1991, 379, 33-53. Gaunitz. U.; Lorenz, W. Z. Phys. Chem. 1992, 776, 121-126. Fawcett, W. R.; Filho, R. C. R. J. Chem. Soc., Faraday Trans. 1992, 88, 1143-1148. Schirmer, H.; Baumgartel, H. J. Electroanal. Chem. 1991, 376, 235- 253. Fontanesi, C. J. Chem. SOC., Faraday Trans. 1992, 88, 3043-3046. Wandlowski, T.; de Levie, R. J. Electroanal. Cbem. 1993, 349, 15-30, Stenina, E. V.; Damaskin, B. B. J. Electroanal. Chem. 1993, 349, 31- 40. Hurwitz, H. D.; Jenard, A.; Bicamumpaka, 6.; Schmickler, W. J. flectroanal. Cbem. 1993, 349, 49-72. Thomas, F. G. J. Elechoanal. Chem. 1993, 349, 81-92. Zutlc, V.; Kovac, S.; Tomaic, J.; Svetlicic, V. J. Electroanal. Chem. 1993, 349, 173-186. Wandlowski. Th.; Chaiyasith, P.; Baumgartl, H. J. Electroanal. Chem. 1993, 346, 271-279. Buess-Herman, C.; Franck, C.; Gierst, L. J. Electroanal. Chem. 1992, 329, 91-102. Wandlowski, T.; delevie, R. J. Electroanal. Chem. 1992,329, 103-127. Benedetti. L.; Gavioli, G. 6.; Fontanesi, C. J. Chem. Soc., Faraday Trans.

Nikitas, P.; Pappa-Louisi, A. Electrochim. Acta 1993, 38, 1573-1584. Pama-Loulsi, A.: Nikitas. P.: Andonwlou, P. Electrochim. Acta 1993,

1992, 88, 843-847.

38: '1585-1590. Thomas, F. G.; Buess-Herman, C. J. Electroanal. Chem. 1991, 378, 399-405.

37, 2663-2672. Wandlowski, T.; Heyrovsky. M.; Novotny, L. Electrochim. Acta 1992,

Jurkiewicz-Herbich, M. J. Electroanal. Chem. 1992, 332, 265-278. Werner, L.; Marlow, F.: Hill, W.; Retter, U. Chem. Phys. Lett. 1992, 794, 39-44. Demoz, A.; Harrison, D. J. Langmuir 1993, 9, 1046-1050. Parsons, R.; Payme, R. J. Electroanal. Chem. 1993, 357, 327-338. Parsons, R.; Peat, R. J. Chem. Soc.. Faraday Trans. 1993, 89, 181- 186. Ribes, A. J.; Osteryoung, J. J. Electroanal. Chem. 1991, 779,311-330. Garrido, J. A.; Robriguez, R. M.; Bastida, R. M.; Brlllas, E. J. Electroanal. Chem. 1992, 324, 19-32. Wandlowski, T.; de Levie, R. J. Elechoanal. Chem. 1993, 345, 413- 432. Wandlowski, Th. J. Electroanal. Chem. 1992, 333, 77-91. Wandlowski. T.: de Levie. R. Collect. Czech. Chem. Commun. 1993, 58, 29-40. Papadopoulos, N.; Sotiropoulos, S.; Niktas, P. J. Elecfroanal. Chem.

Tomaic, J.; Legovic, T.; Zutic, V. J. Electroanal. Chem. 1992, 322, 1992, 324, 375-385.

79-92

58, 29-40. PaDadODOUlOS, N.; Sotiropoulos, S.; Niktas, P. J. Elecfroanal. Chem. 1902, 324, 375-385. Tomaic, J.; Legovic, T.; Zutic, V. J. Electroanal. Chem. 1992, 322, 79-92. . -

Baiazs, G. 6.; Anson, F. C. J. Electroanal. Chem. 1992, 335, 75-82. Balazs, G. B.; Anson, F. C. J. Electroanal. Chem. 1992, 322,325-345. Jaworski, J. S.; Kebede, 2.; Malik, M. J. Elechoanal. Chem. 1992, 333, 371-378. Pizeta, I.; Lovric. M.: Zelic, M.: Branica, M. J. Electroanal. Cbem. 1991,

Anastopoulos, A.; Kaisheva, M. J. Electroanal. Chem. 1991,377, 279- 284. Philipp, R.; Retter. U. Thin Sol@ Films 1992, 207, 42-50. Mattsson, G.; Nyholm, L.; Peter, L. M. J. Electroanal. Chem. 1993, 347, 303-326. Kikuchi, K.; Murayama, T. Bull. Chem. SOC. Jpn. 1993, 66, 437-443. Kruiit. W. S.: Sluvters-Rehbach. M.: Sluvters. J. H. J. flectroanal. Chem.

378, 25-38.

1993, 357, 115-135. Kneten, K. R.; McCreery, R. L. Anal. Chem. 1992, 64, 2518-2524. McDermott, M. T.; Kneten, K.: McCreery, R. L. J. Phys. Chem. 1992, 96. 3124-3130. Alsmeyer, D. C.; McCreery, R. L. Anal. Chem. 1992, 64, 1528-1533. McDermott, C. A.; Kneten, K. R.: McCreew, R. L. J. Electrochem. SOC. 1993, 740, 2593-2599. Alsmeyer. Y. W.; McCreery, R. L. Langmuir 1991, 7, 2370-2375. Sagara, T.; Niki, K. Langmuir 1993, 9, 831-838.

(E88) Goss, C. A.; Brumfield, J. C.; Irene, E. A,; Murray, R. W. Anal. Chem.

(E89) Hendrlcks. S. A.: Kim. Y.-T.: Bard, A. J. J. Electrochem. SOC. 1992, 1993, 65, 1378-1389.

739, 2818-2824. McCarley, R. L.; Hendricks, S. A.; Bard, A. J. J. Phys. Chem. 1992, 96, 10089-10092 . - - - . . - - - . Zubimendl, J. L.; Vazquez, L.; Ocon, P.; Vara, J. M.; Triaca, W. E.; Salvarezza, R. C.; A ~ i a , A. J. J. Phys. Chem. 1993, 97, 5095-5102. Srlnivasan, R.; Gopalan, P. J. Phys. Chem. 1993, 97, 8770-8775. Keita, B.; Nadjo, L. J. Electroanal. Chem. 1993, 354, 295-296. Pocard, N. L.; Alsmeyer, D. C.; McCreecy, R. L.; Neeman, T. X.; Callstrom, M. R. J. Mater. Chem. 1992, 2, 771-784. Pontlkos. N. M.; McCreery, R. L. J. Electroanal. Chem. 1992, 324, 229-242. McDermott, M. T.; McDermott, C. A,; McCreery, R. L. Anal. Chem.

Jaworski, R. K.; McCreery, R. L. J. Electrochem. SOC. 1993, 140, 1360- 1365. Zhang, H.; Coury, L. A., Jr. Anal. Chem. 1993, 65, 1552-1558. Firouzi, A.; Atanasoski, R. T.; Smyrl, W. H. J. Electroanal. Chem. 1992,

Barbero, C.; Kotz, R. J. Electrochem. SOC. 1993, 140, 1-6. Marsh, J. H.; Orchard, S. W. Carbon 1992, 30, 895-901. Pocard, N. L.; Alsmeyer, D. C.; McCreery, R. L.; Neenan, T. X.; Callstrom, M. R. J. Am. Chem. Soc. 1992, 114, 769-771. Hutton, H. D.; Huang, W.; Alsmeyer, D. C.; Kometanl, J.; McCreery, R. L.: Neenan. T. X.: Calistrom. M.R. Chem. Mater. 1993. 5. 1110-1117.

1993, 65, 937-944.

330, 369-380.

(E104) Tateishi, N:: Nishimura, K.; Yahikozawa, K.; Nakagawa,'M.; Yamada, M.; Takasu, Y. J. Electroanal. Chem. 1993, 352, 343-352.

(E105) Ragoisha, G. A.; Jovanovic, V. M.; Aramov-Ivic, M. A.; Atanasoskl, R. T.; Smyrl, W. H. J. Electroanal. Chem. 1991, 379, 373-379.

(E106) Casella, I. G.; Cataldi, T. R. I.; Saki, A. M.; Desimoni, E. Anal. Chem. 1993, 65, 3145-3150.

(E107) Kulesza, P. J.; Lu, W.; Faulkner, L. R. J. Electroanal. Chem. 1992, 336, 35-44.

(E108) Grinberg, V. A.: Kanevskii, L. S.; Cheblakova, E. G.; Mazln, V. M.; Dribinskii, A. V.; Cherstov, V.; Sterlln, S. R.; Vassll'ev, Yu. B. ElektYokhim

(E109) Dribinskii, A. V.; Grinberg, V. A.; Kanevskii, L. S.; Avdalyan, M. 6.; Yakushev, V. V. Elektrokhimlya 1992, 28, 1718-1722.

(El 10) Kaplan, G. I.; Potapova, G. F.; Smlrnov, V. A. Elektrokhmlya 1993,29, 276-278.

(El 11) Chandrasekaran, M.; Noel, M.; Krishnan, V. Collect. Czech. Chem.

(El 12) Chandrasekaran, M.; Noel, M.; Krlshnan, V. J. Appl. Electrochem. 1992,

(E113) Delamar. M.; Hitmi, R.; Pinson, J.; Saveant, J.-M. J. Am. Chem. SOC.

(El 14) Bourdillon, C.; Delamar, M.; Demallle, C.; Hitmi, R.; Molroux, J.; Pinson,

(El 15) Pantano, P.; Kuhr, W. G. Anal. Chem. 1993, 65, 2452-2458. (El 16) Kawagoe, K. T.; Garris, P. A.; Wightman. R. M. J. Electroanal. Chem.

(E117) Self, T. J.; Cresplt, F. J. Mater. Sci.: Mater. Med. 1992, 3, 418-425. (E118) Chun, B. W.; Davls, R. C.; He, Q.; Gustafson, R. R. Carbon 1992, 30,

(El 19) Swain, G. M.; Kuwana, T. Anal. Chem. 1992, 64, 565-568. (E120) Thecdoridou, E.; Jannakoudakis, A. D.; Jannakoudakis, P. D.; Antoniadou,

(E121) Antonladou, S.; Jannakoudakis, A. D.; Jannakoudakis, P. D.; Theodoridou,

(E122) Potje-Kamloth, K.; Josowicz, M. Ber. Bunsenges. Phys. Chem. 1992,

(E123) Nakahara. M.; Shlmizu, K. J. Mater. Sci. 1992, 27, 1207-1211. (E124) Milhn, K. M.; Mikkelsen, S. R. Anal. Chem. 1993, 65, 2317-2323. (E125) McFadden, C. F.; Russell, L. L.; Melaragno, P. R.; David, J. A. Anal.

(E126) Seeliger, W.; Hamnett, A. Ekctrochim. Acta 1992, 37, 763-765. (E127) Kashiwagi, Y.; Ono, H.; Osa, T. Chem. Lett. 1993, 257-260. (E 128) Wang, J.: Angnes, L.; Tobias, H.; Roesner, R. A.; Hong, K. C.; Glass,

R. S.; Kong, F. M.; Pekala, R. W. Anal. Chem. 1993, 65, 2300-2303. (E129) Swain, G. M.; Ramesham, R. Anal. Chem. 1993, 65, 345-351. (E130) Tenne, R.; Patel, K.; Hashlmoto, K.; Fujishima, A. J. Electroanal. Chem.

1993, 347, 409-415. (E131) Wring, S. A.; Hart, J. P. Analyst 1992, 1281-1286. (E132) Gilmartin, M. A. T.; Hart, J. P.; Birch, 8. Analyst 1992, 1299-1303. (E133) Zhao, S.; Korell, U.; Cuccia, L.; Lennox, R. B. J. Phys. Chem. 1992, 96,

(E134) Wang. J.; Naser, N.: Angnes, L.; Wu, H.; Chen, L. Anal. Chem. 1992,

(E135) Kulesza, P. J.; Bandoch, M. J. Elecfroanal. Chem. 1992,323,131-147. (E136) Wdelov. A.: Larsson, R. Electrochlm. Acta 1992, 37, 187-197. (E137) Kobayaski, N.; Janda, P.; Lever, A. B. P. Inorg. Chem. 1992,37,5172-

1992, 28, 864-869.

Commun. 1991, 56, 2055-2066.

22, 1072-1076.

1992, 7 74, 5883-5884.

J. J. Electroanal. Chem. 1992, 336, 113-123.

1993, 359, 193-207.

177-178.

S. Can. J. Chem. 1992, 69, 1881-1885.

E. J. Appl. Electrochem. 1992, 22, 1060-1064.

96, 1004-1017.

Chem. 1992, 64, 1521-1527.

5641 -5652.

64, 1285-1288.

5177 (E138) Atoguchi, T.; Aramata, A.; Kazusaka, A,; Enyo, M. J. Electroanal. Chem.

1991. 378. 309-320. (E139) Zhang, J.; 'Anson, F. C. flectrochim. Acta 1993, 38, 2423-2429. (E140) Zhang. J.; Anson, F. C. J. Elecfmanal. Chem. 1992, 347, 323-341. (E141) Zhang, J.; Anson, F. C. J. ElectroaMl. Chem. 1993, 348, 81-97. (E142) Zhang, J.: Anson, F. C. J. Electroanal. Chem. 1993, 353, 265-280. (E143) Tse, Y.-H.; Seymour, P.; Kobayashi, N.; Lam, H.; Leznoff, C. C.; Lever,

A. B. P. Inorg. Chem. 1991, 30, 4453-4459. (E144) Bond, A. M.; Scholz, F. Langmuir 1991, 7, 3197-3204. (E 145) Bond, A. M.; Colton, R.; Danlels, F.; Fernando, D. R.; Marken, F.; Nagaosa,

Y.; Van Steveninck, R. F. M.; Walter, J. N. J. Am. Chem. SOC. 1993, 7 75, 9556-9562.


(E146) Llorca, M. J.; Feliu, J. M.; Aklaz, A.;Claviller, J.; Rodes, A. J. Elechoanal.

(E1471 Albalat, R.; Claret, J.; Orts, J. M.; Fellu, J. M. J. Elechoanal. Chem. Chem. 1001, 376, 175-197.

1002, 334, 291-307.

Chem. 1902, 340, 213-226. (E1481 Sun, S.4. ; Chen, A.C.; Huang, T.S.; Lln, JA. ; Tlan, 2. W. J. Electroanal.

(E149) Avramoc-Ivlc, M.; Leger, J.-M.; Beden, 6.; Hahn, F.; Lamy, C. J.

(E150) Popovlc, K. 0.; Tripkovic, A. V.; Adzic, R. R. J. Elechoanal. Chem.

(E151) Orts, J. M.; Fellu, J. M.; Aldaz, A. J. Elecfroanal. Chem. 1003, 347,

(E152) Baltruschat, H.; Schmiemann, U. Ber. Bunsenges. Phys. Chem. 1003,

(E153) Schmiemann, U.; Baltruschat, H. J. Elechoanal. Chem. 1902, 340,

(E154) Markovic, N.; Ross, P. N., Jr. J. Phys. Chem. 1003, 97, 9771-9778. (E155) Elswlrth, M.; Lubke, M.; Krlscher, K.; Wolf. W.; Hudson, J. L.; Ertl, G.

(E156) Ye, S.; Klta, H. J. Elechoanal. Chem. 1003, 346, 489-495. (E157) Rodes. A.; Gomez, R.; Orts, J. M.; Feliu, J. M.; AMaz, A. J. Electroanel.

(E158) Ye, S.; Hattori, H.; Klta, H. Ber. Bunsenges. Phys. Chem. 1002, 96,

(E159) Gomez, R.; Orts, J. M.; Rodes, A.; Feliu, J. M.; Aldaz, A. J. Electroanal.

(E160) Nlshlhara, C.; Rasplni, I. A.; Kondoh, H.; Shlndo, H.; Kalse, M.; Nozoye,

(E161) Gamboa-Akleco, M. E.; Herrero, E.; Zelenay, P. S.; Wieckowskl, A. J.

(E162) Faguy, P. W.; Markovlc, N.; Ross, P. N., Jr. J. Electrochem. Soc. 1003,

(E163) Nart, F. C.; Iwaslta, T.; Weber, M. Ber. Bunsenges. Phys. Chem. 1003,

(E164) Marinkovlc, N. S.; Markovic, N. M.; Adzlc, R. R. J. Elechoanal. Chem.

fE165) Llorca. M. J.: Feliu. J. M.: Aldaz. A,: Clavilier, J. J. Electroanal. Chem.

Elechoanal. Chem. 1003, 357, 285-297.

1002, 339. 227-245.

355-370.

97, 452-460.

357-363.

Chem. Phys. Lett. 1992, 792, 254-258.

Chem. 1003, 359, 315-323.

1884- 1885.

Chem. 1903, 358, 267-305.

H. J. Electroanel. Chem. 1002, 338, 299-316.

Elechoanal. Chem. 1093, 348. 451-457.

740, 1638- 164 1.

97, 737-738.

1002, 330, 433-452. , I

1003, '357, 299-319. (E166) Conwav, B. E.; Jerklewicz, G. J. Elechoanal. Chem. 1002, 339, 123- . .

146. (E167) Lang, P.; Claviller, J. Synth. Met. 1001, 45, 297-308. (E168) Upadhyay, D. N.; Kolb, D. M. J. Elechoanal. Chem. 1003, 358, 317-

(E169) Rodes, A.; Claviller, J. J. Electroanal. Chem. 1003, 344, 269-288. (E170) Morallon, E.; Vazquez, J. L.; AMaz, A.; Clavilier, J. J. Elechoanal. Chem.

(E171) Cllment. M. A.: VaHs. M. J.: Feliu, J. M.: Alder, A.;ClavllIer, J. J.Ekfroana/.

325.

1001, 376, 263-274.

(E 172)

(E173) (E174) (E175) (E176)

(E177)

(E178) (E179)

(E180)

(E181)

(E182)

(E183)

(E184)

(E185) (E 186)

(E187) (E188) (E189) (E190) (E191)

(E192)

(E193) (E194) (€195)

(E 196)

(E197)

(E198)

(E199)

(E200)

Chem. 1002, 326, 113-127. Rodes, A.; Clavllier, J.; Orts, J. M.; Feliu, J. M.; Aldaz, A. J. Electroanal. Chem. 1002, 338, 317-338. Sumlno, M. P.; Shibata, S. J. Elechoanal. Chem. 1002,322,391-397. Sumino, M. P.; Shlbata, S. J. Elechoanal. Chem. 1002,336,329-348. Clavilier, J.; Rodes, A. J. Electroanel. Chem. 1003, 348, 247-264. Weaver, M. J.; Chang, S.-C.; Leung, L.-W. H.; Jiang, X.; Rubel, M.; Szklarczvk. M.: Zurawskl. D.: Wlechowski. A. J. E/echoana/. Chem. 1002, 327,' 247-260. Orts, J. M.; Fernandez-Vega, A,; Feilu, J. M.; Aldaz, A.; Clavilier, J. J. Electroanel. Chem. 1002, 327, 261-278. Hamelin, A. J. Elechoanal. Chem. 1002. 329, 247-258. Clavlller, J.; Albaiat, R.; Gomez, R.; Orts, J. M.; Feliu, J. M. J. Electroanal. Chem. 1003, 360, 325-335. Klta, H.; Naruml, H.; Ye, H.; Naohara, H. J. Appl. Electrochem. 1003, 23, 589-596. Clavlller, J.; Albaiat, R.; Gomez, R.; Orts, J. M.; Fellu, J. M.; Aldaz, A. J. Elechoanal. Chem. 1002, 330, 489-497. Morallon, E.; Vazquez, J. L.; Perez, J. M.; Beden, 6.; Hahn, F.; Leger, J. M.; Lamy, C. J. Elecfroanal. Chem. 1003, 344, 289-302. Orts. J. M.; Fellu, J. M.; AMaz, A. J. Electroanal. Chem. 1002, 323,

Franaszczuk, K.; Herrero, E.; Zelenay, P.; Wleckowski, A.; Wang, J.; Masel, R. I. J. Phys. Chem. 1002, 96. 8509-8516. Malta, G. N.; Hubbard, A. T. Cafal. Today 1002, 72, 465-479. Gul, J. Y.; Stern, D. A.; Lln, C. H.; Gao, P.; Hubbard, A. T. Langmuir

Gomez, R.; Clavllier, J. J. Elechoanal. Chem. 1993, 354, 189-208. Zurawski, D.; Wleckowski, A. Langmuir 1092, 8, 2317-2323. Lynch, M. L.; Corn, R. M. J. Elechoanal. Chem. 1001, 378, 379-386. Chang, S. C.; Ho, Y.; Weaver, M. J. Surf. Scl. 1002, 265, 81-94. Campbell, S. A.; Parsons, R. J. Chem. Soc., Faraday Trans. 1002, 88, a33-a41

303-3 18.

1001, 7, 3183-3189.

- - - - . . . Jlang, X.; Chang, S.-C.; Weaver, M. J. J. Chem. Soc., Faraday Trans. 1993. 89. 223-228. . ~~~ ~~~ ..., ~.

Evans, R. W.; Attard, G. A. J. Electroanal. Chem. 1093, 345,337-350. Markovic, N.; Ross, P. N. Langmuir 1003, 9, 580-590. Michaelis, R.; Zel. M. S.: Zhai, R. S.; Kolb, D. M. J. Elechoanal. Chem. 1002, 339. 299-310. Dakkourl. A. S.; Batina, N.; Koib, D. M. Elecfrochlm. Acta 1003, 38, 2407-2472. shaft, D. P.; Twomey, T.; Plleth, W.; Schumacher, R.; Meyer, H. J. Elechoanal. Chem. 1002, 322, 279-268. Adzlc, R. R.; Feddrlx, F.; Nikolic, B. 2.; Yeager, E. J. Electroanal. Chem. 1002, 347, 287-306. Varga, K.; Zelenay, P.; Horlnyi, G.; Wieckowski, A. J. Elechoanal. Chem. 1002, 327, 291-306. Varga, K.; Zelenay, P.; Wieckowski, A. J. Elecfroanal. Chem. 1002, 330, 453-467.

(E201) Michaelis. R.; Kolb, D. M. J. Elechoanal. Chem. 1092, 329, 341-346. (E202) Sashikata, 361-368. K.; Furuya. N.; Itaya, K. J. Elechoanal. Chem. 1001, 376,

(E203) Leung, L. W.; Gregg, T. W.; Goodman, D. W. Langmulr 1001, 7,3205-

(E2041 Leung, L. W.; Oregg, T. W.; Goodman. D. W. Chem. Phys. Lett. 1002,

(E205) Gibson, N. C.; Savllle. P. M.; Harrlngton, D. A. J. Elechoanal. Chei.

(E206) Zelenay, P.; Gamboa-Aldeco, M.; Horanyl, G.; Wieckowskl, A. J.

(E207) Rodrlquez, J. F.; Taylor, D. L.; Abruh, H. D. Elechochlm. Acta 1003,

(E208) Inukal, J.; Ito, M. J. Elechoanal. Chem. 1003, 358, 307-315. (E209) Gomez, R.; Llorca. M. J.; Feliu, J. M.; Aldaz, A. J. Elechoanal. Chem.

(E210) Ross, P. N.; D'Agostlno, A. T. Ektrochlm. Acta 1002, 37, 615-623. (E211) Sholuda, P.; Kolb, D. M. Surf. Sci. 1002, 260, 229-234. (E212) Gao, X.; Weaver, M. J. J. Phys. Chem. 1003, 978685-8689. (E213) McCarley, R. L.; Bard, A. J. J. Phys. Chem. 1001, 95, 9618-9620. (E214) Tao, N. J.; Lindsay, S. M. J. Phys. Chem. 1092, 96, 5213-5217. (E215) Tao, N. J.; Lindsay, S. M. Surf. Scl. Lett. 1002, 274, L546-L553. (E216) Hamelin, A.; Gao, X.; Weaver, M. J. J. Elecfroanal. Chem. 1902, 323,

(E217) Gao, X.; Hamelin, A.; Weaver, M. J. Phys. Rev. B. 1002, 46, 7096. (E218) Skoluda, P.; Ha", U. W.; Kolb, D. M. J. Elechoanal. Chem. 1003,354,

(E219) Sun,S.G.;Yang,D.-F.;Wu,S.J.;Oclepa, J.;Lipkowski. J. J.E/ectroanel.

(E220) Ha". U. W.; Kolb, D. M. J. Elechoanal. Chem. 1002, 332,339-347. (E221) Kim, Y.-T.; McCatley, R. L.; Bard, A. J. J. Phys. Chem. 1002, 96,7416-

(E222) Skoluda, P.; Holzle, M.; Llpkowskl, J.; Kolb, D. M. J. Elechoanal. Chem.

(E223) McCarley, R. L.; Bard, A. J. J. Phys. Chem. 1002, 96, 7410-4716. (E224) McCartey. R. L.; Kim, Y.-T.; Bard, A. J. J. Phys. Chem. 1003, 97, 211-

(E225) Nichols, R. J.; Beckmann, W.; Meyer, H.; Batina, N.; Kolb, D. M. J.

(E226) Batina, N.; Kolb, D. M.; Nichols. R. J. Langmulr 1002, 8, 2572-2576. (E227) Gao, X.; Weaver, M. J. J. Am. Chem. SOC. 1002, 774, 9544-9551. (E228) Pettlnger, 8.; Lipkowskl, J.; Mirwald, S.; Friedrich, A. Surf. Scl. 1002,

(E229) Pettlnger, 6.; Lipkowski, J.; Mirwald, S.; Friedrich, A. J. Elechoanal.

(E230) Koas, D. A.; Richmond, G. L. J. Phys. Chem. 1092, 96, 3770-3775. (E231) Ullmann, R.; Will, T.; Kolb, D. M. Chem. Phys. Lett. 1993,209,238-242. (E2321 Tao, N. J.; Pan, J.; LI, Y.; Oden, P. I.; DeRose, J. A.; Lindsay, S. M.

(E233) Chen, C.; Gewlrth. A. A. Phys. Rev. Lett. 1002, 68, 1571. (E234) Samant, M. G.; Borges, 0.; Melroy, 0. R. J. Elechochem. Soc. 1003,

(E235) Suglta, S.; Abe. T.; Itaya. K. J. Phys. Chem. 1003, 97, 8780-8785. (E236) Chen, C.; Vesecky, S. M.; Gewlrth, A. A. J. Am. Chem. SOC. 1002, 7 74,

(E237) Chen, C.; Washburn, N.; Gewlrth, A. A. J. Phys. Chem. 1003, 97.9754-

(E238) Chen, C.; Gewlrth. A. A. J. Am. Chem. Soc. 1002, 774, 5439-5440. (E239) Chen, C.; Kepler, K. D.; Gewlrth, A. A.; Ocko, B. M.; Wang, J. J. Phys.

(E240) Villegas, I.; Stlckney, J. L. J. Electrochem. SOC. 1002. 739. 686-694. (E241) Vlliegas, I.; Stlckney, J. L. J. Vac. Sci. Techno/., A 1002, 70, 3032-

(E242) Golan, Y.; Margulls, L.; Rubenstein, I.; nodes, 0. Langmulr 1002, 8,

(E243) Skoluda, P.; Dutkiewlcz, E. J. Electroanal. Chem. 1092,329, 279-287. (E244) Richer, J.; Iannelli, A.; Lipkowski, J. J. Electroanal. Chem. 1002, 324,

(E245) Stolberg, L.; Lipkowski, J.; Irish, D. E. J. Electroanal. Chem. 1002, 322,

(E2461 Yang, D. F.; Stolberg, L.; Lipkowskl, J.; Irish, D. E. J. Elechoanal. Chem.

(E247) Tao, N. J.; DeRose, J. A.; Lindsay, S. M. J. Phys. Chem. 1903, 97.910. (E248) No& J. J.; Blzzotto, D.; Llpkowski, J. J. Elechoanal. Chem. 1003, 344,

(E249) Lecoeur, J.; Bellier, J. P.; Koehler. C. J. Elechoanal. Chem. 1092, 337,

(E250) Xing, X.; Shao, M.; Hslao, M. W.; Adzlc, R. R.; Llu, C . C . J. Elechoanal.

(E251) Hamelln. A.; Forestl, M. L.; Guldelii, R. J. Elechoanal. Chem. 1003,346,

(E252) ForesB, M. L.; GuMelll, R.; Hamelln. A. J. Electroenal. Chem. 1003.346,

(E253) Jovic, V. D.; Parsons, R.; Jovic. B. M. J. Elechoanal. Chem. 1002, 339.

(E2541 Doubova. L. M.; Hamelln, A.; Stoicoviciu, L.; Trasatti, S. J. Elechoanal.

(E2551 CaO, E. Y.; -0. P.; Gul, J. Y.; Lu, F.; Stern, D. A,; Hubbard, A. T. J.

(E256) Stalkov, G.; Budevski, E.; Obretenov, W.; Lorenz, W. J. J. Elechoanal.

(E257) Mao, B. W.; Tian. 2. Q.; Fieischmann. M. Elechochlm. Acta 1002. 37, 1767-1770.

(E258) Lorenz, W. J.; Gassa, L. M.; Schmldt, U.; Obretenov, W.; Staikov, 0.; Bostanov, V.; Budevski, E. Elechochlm. Acta 1002, 37, 2173-2178.

3210.

188, 467-470.

1001. 378, 271-282.

Elechoanal. Chem. 1903, 357, 307-326.

38, 235-244.

1002, 340, 3490-355.

361-367.

289-294.

Chem. 1003, 349, 211-222.

7421.

1003. 358, 343-349.

215.

Elechoanal. Chem. 1002, 330, 381-394.

269-270, 377-382.

Chem. 1002, 329, 289-31 1.

Surf. Sc;. Lett 1002, 277, L338-L344.

740, 421-425.

451-458.

9760.

Chem. 1003, 97, 7290-7294.

3038.

749-752.

339-358.

357-372.

1992, 329, 259-278.

343-354.

197-216.

Chem. 1002. 339, 211-225.

251-259.

73-83.

327-337.

Chem. 1002, 325, 197-205.

Elechoanal. Chem. 1002, 339, 31 1-325.

Chem. 1003, 349, 355-363.


(E259) McBride, J. R.; Schlmpf, J. A.; Soriaga, M. P. J. Am. Chem. SOC. 1002,

(E260) Berry, G. M.; McBride, J. R.; Schimpf, J. A,; Soriaga, M. P. J. Electroanal.

(E261) McBride. J. R.: SChlmDf, J. A,; Soriaaa. M. P. J. Electroanal. Chem.

774, 10950-10952.

Chem. 1003, 353, 281-287. . ,

1003, 350, 317-320. ' (E262) Lenz, P.; Solomun, T. J. Electroanai. Chem. 1003, 353, 131-145. (E263) Baldauf, M.; Kolb, D. M. Electrochim. Acta 1003, 38, 2145-2153. (E264) Chang, S . 4 . ; Ho, Y.; Weaver, M. J. J. Electrochem. SOC. 1002, 739,

147-152. (E265) Zelenay, P.; Wieckowski, A. J. Electrochem. SOC. 1002, 739, 2552-

(E266) Ahmadi, A.; Evans, R. W.; Attard, G. J. Electroanal. Chem. 1093, 350,

(E267) Cao, E. Y.; Stern, D. A,; Gui, J. Y.; Hubbard, A. T. J. Electroanal. Chem.

2558.

279-295.

1003, 354, 71-86.

10108-10111. (E268) Wang, K.; Chottlner, G. S.; Scherson, D. A. J. Phys. Chem. 1003, 97,

. - . - - . - . . . . (E269) Borges, G. L.; Samant, M. G.; Ashley, K. J. Electrochem. SOC. 1002,

(E270) Cruickshank, B. J.; Sneddon, D. D.; Gewlrth, A. A. Surf. Sci. Lett. 1003,

(E271) Yau. S.-L.: Fan. F.-R. F.; Bard, A. J. J. Electrochem. SOC. 1002, 739,

739, 1585-1568.

28 7, L308-L314. . .

2825-2829. (E272) Vqel, R.; Kamphausen, I.; Baltruschat, H. Ber. Bunsenges. Phys. Chem.

(E273) Gao, X.: Weaver, M. J. Ber. Bunsenges. Phys. Chem. 1003, 97,507- 1902, 96, 525-530.

516. (E274) Schmlckler, W.; WMrig, C. J. Electroanal. Chem. 1002, 336, 213-221. (E275) Henderson, D.; Chan, K.-Y. J. Electroanal. Chem. 1002,330,395-406. (E276) Fotino, M. Rev. Sci. Instrum. 1003, 64, 159-167. (E277) Hocket, L. A.; Creager, S. E. Rev. Scl. Instrum. 1003, 64, 263-264. (E278) Roblnson, R. S.; Wdrig, C. A. Langmulr 1002, 8, 2311-2316. (E279) Bach, C. E.; Nichols, R. J.; Bechmann, W.; Meyer, H.; Schulte, A,;

Besenhard, J. 0.; Jannakoudakis, P. D. J. Electrochem. SOC. 1003, 740, 1281-1283.

8. 2810-2817. (E280) Brumfield, J. C.; Goss, C. A.: Irene, E. A.; Murray, R. W. LangmulrlOO2,

. , -. . -. (E281) Yang, H.; Fan, F A . F.; Yau, S.-L.; Bard, A. J. J. Electrochem. SOC.

1002. 739. 2182-2185. (E282) G0ss;C. A:; Brumfield, J. C.; Irene, E. A,; Murray, R. W. LangmuirlOOP,

(E283) Creager, S. E. J. Phys. Chem. 1002, 96, 2371-2375. (E284) Suglmoto, H.; Shimo, N.; Kltamura, N.; Masuhara, H.; Itaya, K. J.

(€285) Engstrom, R. C.; Small, 6.; Kattan, L. Anal. Chem. 1002, 64, 241-244. (E266) Wlpf, D. 0.; Bard, A. J.; Tallman, D. E. Anal. Chem. 1003, 65, 1373-

(E287) Oppenheim, I. C.; Trevor, D. J.; Chdsey, C. E. D.; Trevor, P. L.; Sieradzki,

(E268) Cruickshank, B. J.; Gewlrth, A. A,; Rynders, R. M.; Alkire, R. C. J.

(E289) Pontifex, G. H.; Zhang, P.; Wang, 2.; Haslett, T. L.; AIMawlawi, D.;

(E290) Li, S.; White, H. S.; Ward, M. D. Chem. Mater. 1002, 4, 1082-1091. (E291) Chen, J.-S.; Devlne, T. M.: Ogletree, D. F.; Salmeron, M. Surf. S d

(E292) Gomez-Rodrlquez, J. M.; Baro, A. M.; Vazquez, L.; Salvarezza. R. C.; Vara, J. M.; A ~ l a , A. J. J. Phys. Chem. 1002, 96, 347-350.

(E293) Lindsay, S. M.; Tao, N. J.; De Rose, J. A.; Oden, P. I.; Lyubchenko, Y. L.; Harrington, R. E.; Shlyakhtenko, L. Biophys. J. 1002, 67, 1570- 1584.

(E294) Allison, D. P.; Bottomley, L. R.; Thundat, T.; Brown, G. M.; Woychik, R. P.; Schrlck, J. J.; Jacobson, K. 6.; Warmack, R. J. Proc. Natl. Acad.

(E295) Engstrom, R. C.; Ghaffarl, S.; Qu, H. Anal. Chem. 1002, 64, 2525- 2529.

(E296) Miller, C. J.; McCord, P.; Bard, A. J. Langmuir 1001, 7, 2781-2787. (E297) Llllard, R. S.; Moran, P. J.; Isaacs, H. S. J. Electrochem. SOC. 1002,

(E298) Llpkowski, J.; Stolberg, L.; Morin, S.; Irish, D. E.; Zelenay, P.; Gamboa,

(E299) Bockrls, J. O'M.; Gamboa-Aldeco, M.; Szklarczyk, M. J. Electroanal.

(E300) Bockrls, J. O M ; Jeng, K.T. J. Eiectroanai. Chem. 1002,330,541-581. (E301) Dicklnson, K. M.: Hanson, K. E.; Fredlein, R. A. Electrochim. Acta 1002,

(E302) Borkowska, 2.; Jarzabek, G. J. Elechoanal. Chem. 1003, 353, 1-17 (E303) Aramata, A.: Toyoshima, I . ; Enyo, M. Electrochim. Acta l W 2 . 37,

(E304) Franaszczuk, K.; Sobkowski, J. J. Electroanai. Chem. 1002, 327, 235-

(E305) Wang, S.-R.; Fedkiw, P. S. J. Electrochem. SOC. 1002, 739, 2519-

(E306) Gasteiger, H. A.; Markovlc, N.; Ross, P. N., Jr.; Cairns, E. J. J. Phys.

(E307) Kunugl, Y.; Nanaku, T.; Chong, Y.-6.; Watanabe, N. J. Electroanai.

(E308) Iwasita, T.; Nart, F. C. J. Eiectroanal. Chem. 1001, 377, 291-298. (E309) Zhang, Y.; Weaver, M. J. Langmuir 1W3, 9, 1397-1403. (E310) Zapien, D. C.; Gul, J. Y.; Stern, D. A.; Hubbard, A. T. J. Eiectroanal.

(E311) Chang, S . 4 . ; Ho, Y.; Weaver, M. J. J. Am. Chem. SOC. 1001, 773,

(E312) Hlavaty. J.; Volke, J. Collect. Czech. Chem. Common. 1002, 57, 429-

8, 1459-1463.

Electroanal. Chem. 1003, 346, 147-160.

1377.

K. Sclence 1001, 254, 687-689.

Eiectrochem. SOC. 1002, 739, 2829-2832.

Moskovlts, M. J. Phys. Chem. 1001, 95, 9989-9993.

1001, 258, 346-356.

SCi. U.S.A. 1002, 89, 10129-10133.

739, 1007-1012.

M.; Wieckowski, A. J. Eiectroanal. Chem. 1903, 355, 147-163.

Chem. 1002, 339, 355-400.

37, 139-141.

13 17-1320.

245.

2525.

Chem. 1003, 97, 12020-12029.

Chem. 1003, 353, 209-215.

Chem. 1002, 330, 469-467.

9506-95 13.

438.

(E313) (E314)

(E315)

(E316) (E317)

(€318) (E319)

(E320)

(E321)

(E322) (E323) (E324) (E325) (E326) (E327) (E328)

(E329) (E330)

(E331)

(E332)

(E333) (E334) (E335) (E336)

(E337)

(E338) (E339)

(E340) (E341) (E342)

(E343) (E344)

(E345)

(E346)

(€347) (E346)

(E349)

(E350)

(E35 1)

(E352)

(E353)

(E354)

(E355) (E356)

Gattrell, M.; Kirk, D. W. J. Electrochem. SOC. 1003. 740, 1534-1540. Rhodes, A.; Perez, J. M.: Orts, J. M.; Fellu, J. M.; Aldaz, A. J. Electroanal. Chem. 1003, 352, 345-352. Weisshaar, D. E.; Walczak, M. M.; Porter, M. D. Langmulr 1003, 9.

Claviller, J.; Svetllcic, V. J. Electroanal. Chem. 1002, 322, 405-409. Svetlicic, V.; Clavllier, J.; Zutlc, V.; Chevalet, J.; Elachi, K. J. Electroanel. Chem. 1093, 344, 145-160. Shu, 2. X.; Bruckenstein, S. J. Electroanai. Chem. 1001,3 77,263-277. Michelhaugh, S. L.: Carrasquillo, A,, Jr.; Sorlaga, M. P. J. Electroanal. Chem. 1001, 7 79, 387-394. Hsiao, Y.-L.; V i , J. E.; Johnson, D. C. J. Electrochem. SOC. 1002, 739,

Brevett, C. A. S.; Johnson, D. C. J. Electrochem. SOC. 1002, 739, 131 4- 13 19. Wllllams, D. G.; Johnson, D. C. Anal. Chem. 1002, 64, 1785-1789. Conway, B. E.; Gu, P. J. Electroanel. Chem. 1003, 349, 233-254. Nakabayashi, S.; Klra, A. J. Phys. Chem. 1002, 96, 1021. Okamoto, H.; Tanaka, N. Electrochim. Acta 1003, 38, 503-509. Okamoto, H.; Tanaka, N. Electrochim. Acta 1003, 38, 503-509. Okamoto, H. Electrochim. Acta 1002, 37, 37-42. Wolf, W.; Ye, J.; Purgand, M.; EiswCth, M.; Doblhofer, K. Ber. Bunsenges. Phys. Chem. 1002, 96, 1797-1804. InzeR, G.; Kertesz, V. Electrochim. Acta 1003, 38, 2385-2386. Schneider, F. W.; Hauser, M. J. B.; Reislng, J. Ber. Bunsenges. Phys. Chem. 1003, 97, 55-58. Birss, V. I.; Chang, M.; Segal. J. J. Electroanel. Chem. 1003, 355, 181-191. Birss, V. I.; Goledzlnowski, M. J. Electroanel. Chem. 1003, 357, 227- 243. Burke, L. D.; Casey, J. K. Electrochim. Acte 1002, 37, 1617-1829. Burke, L. D.; O'Dwyer, K. J. Electrochim. Acta 1002, 37, 43-50. Heyd, D. V.: Harrington, D. A. J. Electroanel. Chem. 1002,335, 19-31. Schumacher, R.; Helblg, W.; Hass, I.; Wunsche, M.; Meyer, H. J. Electroanai. Chem. 1003, 354. 59-70. Bourkane, S.; Gabrlelli, C.; Keddam, M. Electrochim. Acta 1903, 38,

Burke, L. D.; O'Sullivan, J. F. Electrochim. Acta 1002, 37, 585-594. Burke, L. D.; Cunnane, V. J.; Lee, B. H. J. Electrochem. SOC. 1002, 739,

Roberts, R.; Johnson, D. C. Electroanalysis (N. Y.) 1092, 4, 741-749. Bolzan, A. E.; AN^, A. J. J. Electroanal. Chem. 1003, 354, 243-253. Creus. A. H.; Carro, P.; Gonzalez, S.; Salvarezza, R. C.; ANia, A. J. J. Electrochem. SOC. 1002, 739, 1064-1070. Burstein, G. T.; Clnderey, R. J. Corros. Scl. 1901, 32, 1195-121 1. Peck, S. R.; Curtin, L. S.; McDevitt, J. T.; Murray, R. W.; Collman, J. P.; Little, W. A.; Zetterer, T.; Duan, H. M.; Dong, C.; Hermann, A. M. J. Am. Chem. SOC. 1002, 774, 6771-6775. Engelhardt, 1.; Speck, R.; Inche, J.; Khalil, H. S.; Ebert, M.; Lorenz, W. J.; Saemann-Ischenko, G.; Breiter, M. W. Electrochim. Acta 1002, 37,

323-329.

377-380.

1827-1835.

399-406.

21 29-2136.

114 9702-9704 (;reen, S. J.; Rosselnsky, D. R.; Toohey, M. J. J. Am. Chem. SOC. 1002,

. . , - . - - - . - . . Kuznetsov, A. M. Electrochim. Acta 1002, 37, 2123-2128. Rosamilia, J. M.; Glarum, S. H.; Cava, R. J.; Batlogg, B.; Miller, B. Physica C 1901, 182, 285-290. Bhattacharya, R. N.; Parilla, P. A.; Noufi, R.; Arendt, P.; Elllott, N. J. Electrochem. Soc. 1002, 739, 67-69. Morikawa, Y.; Satoh, K.; Ozawa, S.; Nakamura, K.; Yamamoto, H.; Tanaka, M. Physics C (Amsterdam) 1001, 785- 789, 431-432. Izakovlch, E. N.; Geskin, V. M.: Stepanov, S. V. Synth. Met. 1002, 46, 71-77. Haupt, S. G.; Riley, D. R.; Jones, C. T.; Zhao, J.; McDevitt, J. T. J. Am. Chem. Soc. 1003, 715, 1196-1196. Scheurell, S.: Scholz, F.; Olesch, T.; Kemink, E. Smcond. Sd. Techno/.

Ma, S. M.; Chang, Y. S.; Yang, F. L.; Li, C. S.; Huang, Y. T.; Lee, W. H. J. Electrochem. SOC. 1002, 139, 1951-1955. Nakabayashi, S.; Klra, A. J. Electroanel. Chem. 1001, 779, 381-385. Graves, J. E.: Pletchec, D.; Clarke, R. L.; Walsh, F. C. J. Appl. Electrochem.

1002, 5, 303-305.

lQ92. 22. 200-203. . . . -. --. -. . -. . . (E357) Graves, J. E.; Pletcher, D.;Clarke,R. L.; Walsh, F.C. J. Appl. Ektrochem.

1001. 27. 848-857. (E358) B a c i , R:; Ravindranathan, P.: Dougherty, J. P. J. Mater. Res. 1002,

7, 423-428.

F. MODIFIED ELECTRODES

Frksch-Faules, I.; Faulkner, L. R. J. Electroanai. Chem. 1002, 331,

FrRsch-Faules, 1.; Faulkner, L. R. Anal. Chem. 1002, 64, 11 18-1 127. Fritsch-Faules, I.; Faulkner, L. R. Anal. Chem. 1002. 64, 1127-1131. Larsson, H.; Lindholm, B.; Sharp, M. J. Electroanai. Chem. 1002, 336, 263-279. Blauch, E. N.; Saveant, J . 4 . J. Am. Chem. Soc. 1002, 774, 3323- 3332. Blauch, D. N.; Saveant, J . 4 . J. Phys. Chem. 1003, 97, 6444-6448. Mohan, L. S.; Sangaranarayanan, M. V. J. Electroanal. Chem. 1002,

Delss, E.; Haas, 0.: Daul, C. J. Electroanai. Chem. 1002,337,299-324. Ren. X.: Pickup. P. G. J. Electrochem. Soc. 1002, 739, 2097-2105. Ren, X.; Pickup, P. G. J. Phys. Chem. 1003, 97, 5356-5362. Ren, X.; Pickup, P. G. J. Chem. SOC., Faraday Trans. 1003, 89, 321- 326. Fletcher, S. J. Chem. Soc., Faraday Trans. 1003, 89, 311-320. Fletcher, S. J. Electroanal. Chem. 1002, 337, 127-145.

997-1014.

323, 375-379.

418R Analytical Chemistty, Vol, 66, No. 12, June 15, 1994

Albery, W. J.; Mount, A. R. J. Chem. SOC., Faraday Trans. 1993, 89,

Albery, W. J.; Mount, A. R. J. Chem. Soc., Faraday Trans. 1993, 89,

Mathias, M. F.; Haas, 0. J. Phys. Chem. 1992, 96, 3174-3182. Mathias, M. F.; Haas, 0. J. Phys. Chem. 1993, 97, 9217-9225. Ren. X.; Pickup, P. G. J. Phys. Chem. 1983, 97, 3941-3943. Albery, W. J.; Elliott, C. M.; Mount, A. R. J. Electroanal. Chem. 1990,

Cai, 2.; Marin, C. R. Synth. Met. 1992, 46, 165-179. Sharp, M.; Llndholm-Sethson, B.; Lind, E.-L. J. Electroanel. Chem. 1993,

Forster, R. J.; Vos, J. G. Electrochim. Acta 1992, 37, 159-167. Forster, R. J.; Vos, J. G. J. Electrochem. SOC. 1992, 739, 1503-1509. Lee, C.; Anson, F. C. Anal. Chem. 1992, 64, 528-533. Mao, H.; Pickup, P. 0. Chem. Meter. 1992. 4, 842-645. Aoki, A.; Helier, A. J. Phys. Chem. 1993, 97, 11014-11019. Kelly, A. J.; Oyama, N. J. Phys. Chem. 1991, 95, 9579-9584. Hillman, A. R.; Hughes, N. A.; Bruckenstein, S. J. Electrochem. SOC.

Inzelt, G.; Bacskai, J. Electrochlm. Acta 1992, 37, 647-654. Clarke, A. P.; Vos, J. 0.; Hillman, A. R. J. Electroanal. Chem. 1993,356,

327-331.

2487-2497.

288, 15-34.

345, 223-242.

1992, 139, 74-77.

287-293. Miras,M:C.; Barbero, C.; K&, R.; Haas, 0.; Schmidt, V. M. J. fktroanal. Chem. 1992. 338. 279-297. Kulesza, P. J.; caius, Z. J. E/ectroana/. cbm. 1992, 323, 261-274. Lang, G.; Bacskal, J.; Inzelt, G. Electrochim. Acta 1993,38,773-760. Mlcka, K. flectrochim. Acta 1993, 38, 1433-1439. Amemiya, T.; Hashimoto, K.; Fujishima, A. J. Phys. Chem. 1993, 97,

Amemiya, T.; Hashimoto, K.; Fujishima, A. J. Phys. Chem. 1993, 97,

Hillman, A. R.; Bruckenstein, S. J. Chem. Soc., Faraday Trans. 1993,

Bruckenstein, S.; Wiide, C. P.; Hillman, A. R. J. Phys. Chem. 1993, 97,

Bruckenstein, S.; Hillman, A. R. J. Phys. Chem. 1991, 7997, 10748- 10752. Takehara, K.; Ide, Y. Bioelectrochem. Bloenerg. 1991, 26, 297-305. Tatistcheff, H. 6.; Frltsch-Fauies, I.; Wrighton, M. S. J. Phys. Chem. 1993, 97, 2732-2739. Lyons, M. E. G.; Bartiett, P. N. J. Electroanel. Chem. 1991, 316. 1-22. Lyons, M. E. G.; Lyons, C. H.; Mlchas, A.; Bartlett, P. N. Analyst 1992, 1271-1280. Xie, Y.; Anson, F. C. J. Electroanel. Chem. 1993, 344, 405-411. Xle, Y.; Anson, F. C. J. flectroanal. Chem. 1993, 349, 325-340. Sabatani, E.; Anson, F. C. J. Phys. Chem. 1993, 97, 10158-10165. Shi, C.; Anson, F. C. J. Am. Chem. SOC. 1991. 773, 9564-9570. Zeng, 2. Y.; Gupta, S. L.; Huang, H.; Yeager, E. B. J. Appl. flectrochem.

Kawashima, M.; Sato, Y.; Niushima, K.; Sato, M.; Sakaguchi, M. J. Electroanal. Chem. 1991, 376, 293-304. El Hourch, A.; Belcadi, S.; Moisy, P.; Crouigneau, P.; Leger, J.-M.; Lamy, C. J. Electroanal. Chem. 1992, 339, 1-12. Yoshida, T.; Iida, T.; Shirasagi, T.; Lin, R.J.; Kaneko, M. J. Electroanal. Chem. 1993, 344, 355-362. Ogura, K.; Mine, K.; Yano, J.; Suglhara, H. J. Chem. Soc., Chem. Commun. 1993, 20-2 1. Doherty, A. P.; Vos, J. G. J. Chem. Soc., Faraday Trans. 1992, 88.

Dohertv. A. P.; Forster, R. J.; Smyth, M. R.; Vos, J. G. Anal. Chlm. Acta

4192-41 95.

9736-9740.

89, 339-348.

6853-6858.

1991, 27, 973-981.

2903-2907.

1991, 255, 45-52. Younathan, J. N.; Wood, K. S.; Meyer, T. J. Inorg. Chem. 1992, 37, 3280-3265. Wang, B.; Song, F.; Dong, S. J. €lec?roanal. Chem. 1993, 353,43-55. Dong, S.; Jin, W. J. Electroanel. Chem. 1993, 354, 87-97. Wei, C.; German, S.; Basak, S.; Rajeshwar. K. J. Electrochem. SOC. 1093. 140. L60-L62. . . . -, . . . , -. . -. -. Arai, 0.; Sugaya, T.; Sakamoto, M.; Yasumori, I. Bull. Chem. SOC. Jpn. 1992. 65. 594-596. Furbee, J: W., Jr.; Thomas, C. R.; Kelly, R. S.; Malachowski, M. R. Anal. Chem. 1993, 65, 1654-1657. Deronzier, A.; Moutet, J.4.; Salnt-Aman, E. J. flectroanal. Chem. 1992,

Chardon-Noblat, S.; Cosnler, S.; Deronzier, A,; Vlachopoulos, N. J. Electroanal. Chem. 1993, 352, 213-228. Miaw, C.-L.; Hu, N.; Bobbw, J. M.; Ma, 2.; Ahmadi, M. F.; Rushing, J. F. Langmuir 1993, 9, 315-322. Ohsaka, T.; Tanaka, K.; Tokuda, K. J. Chem. SOC., Chem. Commun.

Kashiwagi, Y.; Osa, T. Chem. Le??. 1993, 677-680. Hale, P. D.; Lee, H A . ; Okamoto, Y. Anal. Le??. 1993, 26, 1073-1085. Cauquls, G.; Cosnier, S.; Deronzier, A.; Galland, 6.; Llmosln, D.; Moutet, J.C.; Bizot, J.; Deprez, D.; Pullcanl, J.-P. J. flectroanal. Chem. 1093,

Wong. K.-Y.; Yam, V. W.-W.; Lee, W. W.4. flectrochlm. Acta 1982,

DeGiovani, W. F.; Deronzier, A. J. flectroanal. Chem. 1992,337,285- 298. Fish, J. R.; Kubaszewskl, E.; Peat, A.; Malinski, T.; Kaczor, J.; Kus, P.; Czuchajowski, L. Chem. Meter. 1992, 4, 795-803. Kubaszewskl, E.; Bennett, J.; Tomboulian, P.; Maiinski, T.; Czuchajowski, L.; Kiechle, F. Appl. Surt Scl. 1993, 65-66, 355-361. Hamnett, A.; Stevens, P. S.; Wingate, R. D. J. Appl. Electrochem. 1991,

327, 147-158.

1993, 222-224.

352, 181-195.

37, 2645-2650.

27. 982-985.

(F73) Ye, L.; Mmmerle, M.; Olsthoorn, A. J. J.; Schuhmann, W.; Schmidt, HA.; Duine, J. A.; Heller, A. Anal. Chem. 1993, 65, 238-241.

(F74) Yon-Hin, B. F. Y.; Smoiander, M.; Crompton, T.; Lowe, C. R. Anal. Chem. 1993, 65. 2067-2071.

(F75) Bartlett, P. N.; Birkin, P. R. Anal. Chem. 1993. 65, 1118-1119. (F76) Anzai. J.; Hoshi, T.; Osa, T. Chem. Le??. 1993, 1231-1234. (F77) Arai, 0.; Hayashi, M.; Noma, T.; Yasumoti, I . Chem. Le??. 1993, 1081-

1064. (F78) Khan, 0. F.; Kobetake, E.; Ikarlyama, Y.; Aizawa, M. Anal. Chlm. Acta

(F79) Wang, D. L.; Helkr, A. Anal. Chem. 1993, 65, 1069-1073. (F60) Vreeke, M.; Malden, R.; Helkr, A. Anal. Chem. 1992, 64.3084-3090. (F81) Tatsuma, T.; Gondalra, M.; Watanabe, T. Anal. Chem. 1922,64, 1183-

1187. (F82) Shl, C.; Anson, F. C. Inorg. Chem. 1992, 37, 5078-5083. (F83) Steiger, B.; Shi, C.; Anson, F. C. Znorg, Chem. 1993, 32, 2107-2113. (F84) Arifuku, F.; Mori, K.; Muratani, T.; Kurihara, H. Bull. Chem. Soc. Jpn.

(F85) Nobayaski, N.; Janda, P.; Lever, A. B. P. Inorg. Chem. 1992,3 1,5172-

1893, 287, 527-533.

1992, 65, 1491-1495.

5177. (F86) Aklba, U.; Nakamura, Y.; Suga, K.; Fujlhira, M. Thln SolMFilms 1992.

(F87) Roslonek, G.; Taraszewska, J. J. Electroanal. Chem. 1992, 325.285- 300.

2 101 2 7 1, 38 1-383.

(F88) Chen, K.; Herr, 8. R.; Singewald, E. T.; Merkin, C. A. Langmuir 1992,

(F89) Verbrugge, M. W.; SchneMer, E. W.; Coneli, R. S.; Hill, R. F. J. Electrochem. Soc. 1992. 739. 3421-3428.

(F90) Zawodzinski, T. A., Jr.; Derouin, C.; Radzinski, S.; Sherman, R. J.; Smith, V. T.; Springer. T. E.; Gottesfeld, S. J. Electrochem. Soc. 1993, 740, 1041-1047.

(F91) Porat, 2.; Rubinstein. I.; Zinger, B. J. Electrochem. Soc. 1993, 740,

(F92) Lin, R.J.; Onikubo, T.; Nagai, K.; Kaneko, M. J. Electroanel. Chem. 1993, 348, 189-199.

(F93) Cha, C. S.; Chen, J.; Liu, P. F. J. flectroanal. Chem. 1993, 345, 463- 467.

(F94) Parthasarathy, A.; Dave, 6.; Srlnivasan, S.; Appiey, A. J.; Martin, C. R. J. Electrochem. SOC. 1992, 139, 1834-1641.

(F95) Parthasarathy, A.; Srinivasan, S.; Appleby, A. J.; Martin, C. R. J. Electrochem. SOC. 1992, 739, 2530-2537.

(F96) Parthasarathy, A.; Srlnivasan, S.; Appleby, A. J.; Martin, C. R. J. Electroanal. Chem. 1992, 339, 101-121.

(F97) Urlbe, F. A.; SDringer. T. E.; Gottesfeid, S. J. Electrochem. Soc. 1992.

8, 2565-2587.

2501-2507.

139, 765-773. - (F98) Amadeili, R.; DeBattisti, A.; Enea, 0. J. Electroanel. Chem. 1992, 339,

85-100.

15-23. (F99) Liu, R.; Her, W.-H.; Fedkiw, P. S. J. Electrochem. Soc. 1982, 739,

(F100) Liu, R.; Fedkiw, P. S. J. Electrochem. Soc. 1982, 739, 3514-3523. (F101) Meli,G.;Leger, J.-M.; Lamy, C.; Durand, R. J. Appl. Electrochem. 1993,

(F102) Inaba, M.; Hlnatsu, J. T.; Oeuml, 2.; Takehara. 2. J. Electrochem. SOC. 234, 197-202.

1993, 740, 706-711.

325 351-357 (F103) Van Ryswyk, H.; Kim, C. H.; Staley, T. A. J. Electroanal. Chem. 1992,

- - -, - - . - - . . (F104) Ugo, P.; Ballarin, B.; Danieie, S.; Mazzocchin, G. A. J. Elechoanal.

(F105) Audebert, P.; Divisia-Blohorn, B.; Aldebert, P.; Michalak, F. J. Eleciraanal.

(F 106) Toniolo, R.; BontemDeili. G.; Schiavon. G.; Zotti, G. J. Electroanel. Chem.

Chem. 1992, 324. 145-159.

Chem. 1992, 322, 301-309.

1993, 356, 67-80.’ (F107) Schiavon, G.; Zotti, G.; Toniolo, R.; Bontempelli, G. Anal. Chim. Acta

(F108) Xu, M.; Horsthemke, W.; Schell, M. Electrochim. Acta 1983, 38, 919- 1892, 264, 221-228.

925. (F109) diCastro-Martins, S.; Khouzani, S.; Tuel, A.; Taarit, Y. B.; El Murr, N.;

(F1 IO) Bedloui, F.; DeBoysson, E.; Devynck, J.; Balkus, K. J., Jr. J. Chem. SOC.,

(F111) Baker, M. D.; Senaratne, C.; Zhang, J. J. Chem. Soc., Faraday Trans.

Sellami, A. J. Electroanel. Chem. 1993, 350, 15-28.

Faraday Trans. 1991, 87, 3831-3834.

1892, 88, 3167-3192.

3533 (F I 12) Petridis, D.; Falaras, P.; Plnnavaia. T. J. Inorg. Chem. 1992, 37,3530-

(F113) Brahlmi, B.; Labbe, P.; Reverdy. G. Langmuir 1982, 8, 1908-1918. (F114) Fitch, A.; Lee, S. A. J. Elechoanal. Chem. 1993, 344, 45-59. (F115) Kaviratna, P. Des.; Pinnavaia, T. J. J. Electroanal. Chem. 1992, 332,

(F116) Rong, D.; Mallouk, T. E. Inorg. Chem. 1993, 32, 1454-1459. (F117) Kutner, W. flectrochlm. Acta 1992, 37, 1109-1117. (F118) Kutner, W.; Dobihofer, K. J. Electroanal. Chem. 1992, 326, 139-160. (F119) Lepretre, J.-C.; Salnt-Aman, E.; Utilie, J.-P. J. Electroanal. Chem. 1993,

(F120) Limoges, B.; Degrand, C.; Brossier, P.; Blankespoor, R. L. Anal. Chem. 1993, 65, 1054-1060.

(F121) La Salle, A. L. G.; Limoges, B.; Anizon, J. Y.; Degrand. C.; Brossier, P. J. flectroanal. Chem. 1893, 350, 329-335.

(F122) Wang, E.; Liu, A. Microchem. J. 1991, 44, 327-334. (F123) Gorskl, W.; Cox, J. A. Anal. Chem. 1992. 64, 2706-2710. (F124) Lorenzo, E.; AbruRa, H. D. J. flectroanal. Chem. 1992, 328, 111-125. (F125) Tleman, R. S.; Heineman, W. R. Anal. Le??. 1992, 25, 807-819. (F126) Huang, J.; Wrighton, M. S. Anal. Chem. 1993, 65. 2740-2746. (F127) Mao, H.; Pickup, P. G. J. Phys. Chem. 1992, 96, 5604-5610. (F128) ai, 2.; Pickup, P. G. J. Electroanal. Chem. 1993, 355. 133-146. (F129) Basak, S.; Bose, C. S. C.; Rajeshwar, K. Anal. Chem. 1992, 64, 1613-

135-145.

347, 465-470.

1818.


(F130)

(F131)

(F132)

(F133)

(F134)

(F135)

(F136)

(F137) (F138)

(F139) (F140) (F141)

(F142)

(F143)

(F144)

(F145)

(F146) (F147)

(F148)

(F149)

(F150)

(F151) (F152) (F153) (F154) (F155) (F156)

(F157) (F158)

(F159)

Yano, J.; Shimoyama, A.; Ogura, K. J. Chem. Soc., Faraday Trans. 1992. 88. 2523-2527. ~~, ~

Bose, C. S. C.; Basak. S.; Rajeshwar, K. J. Phys. Chem. 1992, 96, 9899-9906. Chesher, D. A,; Christensen, P. A,; Hamnett, A. J. Chem. Soc.. Faraday Trans. 1993, 89, 303-309. Pyo, M.; Reynolds, J. R . J. Chem. Soc., Chem. Commun. 1993, 158- 260. Yue, J.; Epstein, A. J. J. Chem. Soc., Chem. Commun. 1992, 1540- 1542. Duffitt, G. L.; Pickup, P. G. J. Chem. Soc., Faraday Trans. 1992, 88, 14 17- 1423. Schmidt, V. M.; Barbero, C.; Kotz, R. J. Electroanal. Chem. 1993, 352, 30 1-307. Novak, P.; Kotz, R.; Haas, 0. J. Electrochem. SOC. 1993, 140, 37-40. Barbero, C.; Miras, M. C.; Kotz. R. flectrochlm. Acta 1992, 37, 429- 437. Chen, C. C.; Wei, C.; Rajeshwar, K. Anal. Chem. 1993,65,2437-2442. Li, Y.; Dong, S. J. Chem. Soc., Chem. Commun. 1992, 827-828. Hepel, M.; Seymour, E.; Yogev, D.; Fendier, J. H. Chem. Mater. 1992, 4, 209-216. Deronizier, A.; Marques, M.J. J. Electroanal. Chem. 1992, 334, 247- 261. Wooster, T. T.; Watanabe, M.; Murray, R. W. J. Phys. Chem. 1992, 96, 5886-5893. Watanabe, M.; Nagasaka, H.; Sanui, K.; Ogata, N.; Murray, R. W. Electrochim. Acta 1992, 37, 1521-1523. Baril, D.; Chabre, Y.; Armand, M. 9. J. Electrochem. SOC. 1993, 140, 2687-2690. Che, G.; Dong, S. Electrochim. Acta 1993, 38, 2315-2319. Third International Symposium on Polymer flectrolytes; Armand, M., Gandini, A., Eds. Electrochim. Acta 1992, 37, 1469-1745. Nishihara. H.: Ohta, M.; Aramaki. K. J. Chem. SOC., Faraday Trans. 1992, 88, 627-831. Shi, G.: Xue, G.; Wu, Z.; Shen, 8. J. Electroanal. Chem. 1992, 338, 352-257. Velazquez, C. S.; Hutchison. J. E.; Murray, R. W. J. Am. Chem. SOC. 1993, 115, 7896-7897. Sullenberger, E. F.; Michael, A. C. Anal. Chem. 1993, 65, 2304-2310. Turyan, I.; Mandler, D. Nature 1993, 362, 703-704. Saiamon, Z.; Tollin, G. J. flectroanal. Chem. 1992, 342, 381-391. Nelson, A. J. Electroanal. Chem. 1992, 335, 327-343. Rojas, M. T.; Han, M.; Kalfer, A. E. Langmulr 1992, 8, 1627-1632. Doyle, M.; Fuller, T. F.; Newman, J. J. Electrochem. SOC. 1993, 140, 1526-1533. Nahir, T. M.; Buck, R. P. J. Electroanal. Chem. 1992, 341, 1-14. Albagli, D.; Bazan, G.; Wrighton M. S.; Schrock, R. R . J. Am. Chem. SOC. 1992, 114, 4150-4158. Nauven. M. T.: Diaz, A. F.; Dement'ev. V. V.; Pannell, K. H. Chem. Miter. 1993, 5, 1369-1394.

(F160) Ikeda, S.; Oyama, N. Anal. Chem. 1993, 65, 1910-1915. (F161) Oyama,N.;Tatsuma,T.;Takahashi.K. J. Phys.Chem. 1993,97,10504-

10508.

1992, 784-786.

Chem. 1992, 324, 325-337.

J.-P. J. Am. Chem. SOC. 1992, 114, 5966-5994.

(F162) Segawa, H.; Nakayama, N.; Shimidzu, T. J. Chem. Soc., Chem. Commun.

(F163) Deronzier, A,; Devaux, R.; Limosin, D.; Latour. J.-M. J. Electroanal.

a-Blohorn, 9.; Lapkowski, M.; Kern, J.-M.; Sauvage,

(F165) Pickett, C. J.; Ryder. K. S.; Moutet, J.4. J. Chem. SOC., Chem. Commun.

(F166) Bommarito, S. L.; Lowery-Bretz, S. P.; Abruiia. H. D. Inorg. Chem.

(F167) Bommarito, S . L.; Lowery-Bretz, S. P.; Abrufia, H. D. Inorg. Chem.

(F168) Subramanian, P.; Zhang, H.-T.; Hupp, J. T. Inorg. Chem. 1992, 31,

(F169) Hable, C. T.; Crooks. R. M.; Valentine, J. R.; Giasson, R.; Wrighton, M.

(F170) Hatozaki. 0.: Ohsaka, T.; Oyama, N. J. Phys. Chem. 1992, 96, 10492-

(F 17 1) Katz, E.; delacey, A. L.; Fierro, J. L. G.; Palacios, J. M.; Fernandez,

(F172) Katz, E.; delacey, A. L; Fernandez, V. M. J. Electroanal. Chem. 1993,

(F173) Huang. S.; Song, X.; Lin, H.; Yu, R. Mlkrochim. Acta 1992, 107, 27-36. (F174) Gache, Y.; Simonet, J. J. Chlm. Phys. Phys.-Chlm. Blol. 1992,89, 1027-

(F175) Horak, V.; Weeks, G. Bloorg. Chem. 1993, 21, 24-33. (F176) Bartlett, P. N.; Dawson. D. H.; Farrington, J. J. Chem. Soc., Faraday

(F177) Thobie-Gautier, C.; Gorgues, A.; Jubauit, M.; Roncali, J. Macromolecules

(F178) Fourmigue, M.; Johannsen, I.; Boubekeur, K.; Nelson, C.; Batail, P. J.

(F179) Katz, E. Y.; Borovkov, V. V.; Evstigneera, R. P. J. flectroanal. Chem.

(F180) Albagli, D.; Bazan, G. C.; Schrock, R. R.; Wrighton. M. S. J. Am. Chem.

(F181) Stilwell, D. E.; Park, K. H.; Miles, M. H. J. Appl. Electrochem. 1992, 22,

(F182) Moon, S. 6.; Xidis, A.; Neff. V. D. J. Phys. Chem. 1993, 97, 1634-1638. (F183) Kuiesza, P. J.; Chelmecki. G.; Gaiadyk, B. J. flectroanai. Chem. 1993,

(F184) Jiang, M.; Wang, M.; Zhou, X. Chem. Lett. 1992, 1709-1712.

1992, 694-697.

1992, 31, 502-507.

1992, 31, 495-502.

1540- 1542.

S. J. Phys. Chem. 1993, 97, 6060-6065.

10497.

V. M. J. Electroanal. Chem. 1993, 358, 247-259.

358, 261-272.

1035.

Trans. 1992, 88, 2685-2695.

1993, 26, 4094-4099.

Am. Chem. SOC. 1993, 115, 3752-3759.

1992, 326, 197-212.

SOC. 1993, 115, 7326-7334.

325-331,

34% 417-423.

(F185) Luangdilok, C. H.; Arent, D. J.; Bocarsly, A. 9.; Wood, R. Langmulr 1992. 8. 650-657.

(F186) Zhou, J.; Wang, E. J. Electroanal. Chem. 1992, 331, 1029-1043. (F187) Pllchon, V.; Besbes, S. flectrochim. Acta 1992, 37, 501-506. (F188) Xidis, A.; Neff, V. D. J. Electrochem. SOC. 1991, 138, 3637-3642. (F189) Kondratev,V. V.;Vlnokurov, I.A.;Bertsev,V.V.;Khakin. S.Y.;Zelenina,

(F190) Yoneyama. H.; Takahashi. N.; Kuwabata, S. J. Chem. SOC., Chem.

(F191) Kuwabata. S.; Takahashi, N.; Hirao, S.; Yoneyama. H. Chem. Mater.

0. M. Elektrokhlmiya 1992, 28, 74-80.

Commun. 1992, 716-717.

1993. 5 437-441. ._, -. . (F192) Collomb-Dunand-Sauthier. M.-N.; Deronzier, A.; Zlessel, R. J. Phys.

(F193) Kuwabata, S.; Mitsui, K.; Yoneyama, H. J. Electrochem. SOC. 1992, Chem. 1993, 97, 5973-5979.

139. 1824-1630. (F194) Argiis. P.; Srinivas, R. A.; Carls, J. C.; Heller, A. J. flectrochem. SOC.

(F195) GouM, S.; Gray, K. H.; Linton, R. W.; Meyer, T. J. Inorg. Chem. 1992,

(F196) Sawai, T.; Yamazaki, S.; Ishigami, Y.; Ikariyama, Y.; Alzawa, M. J.

(F197) Miyasaka, T.; Koyama, K.; Itoh, I. Science 1992, 255, 342. (F198) Wollman, E. W.; Frisbie, C. D.; Wrighton, M. S. Langmulr 1993, 9.

(F199) Nishizawa, M.; Miwa, Y.; Matsue, T.; Uchida, I. J. Electrochem. SOC.

(F200) Nishizawa, M.; Shibuya, M.; Sawaguchl, T.; Matsue. T.; Uchida, I. J.

(F201) Fuiii. M.: Arii. K.: Yoshino. K. J. Electrochem. SOC. 1993. 140. 1838-

1992, 139, 2889-2894.

31, 5521-5525.

Electroanal. Chem. 1992, 322, 1-7.

15 17- 1520.

1993, 140, 1650-1655.

Phys. Chem. 1991, 95, 9042-9044.

(F202) (F203)

(F204)

(F205)

(F206)

(F207) (F208)

(F209)

(F210)

(F211)

(F212) (F213) (F214)

(F215)

(F216)

(F217)

(F218) (F219)

(F220) (F221)

(F222)

(F223)

(F224)

(F225) (F226) (F227) (F228)

(F229) (F230) (F231) (F232)

(F233)

(F234) (F235)

(F236)

(F237)

(F238) (F239) (F240)

(F241) (F242)

. . 1842. Jin, J.-Y.; Teramae. N.: Haraguchi, H. Chem. Left. 1993, 101-104. Rodriguez-Mendez. M. L.: Aroca, R.; DeSaja, J. A. Chem. Mater. 1992, 4, 1017-1020. Toshima, N.; Kawamura, S.; Tominaga, T. Chem. Len. 1993, 1299- 1302. Saika, T.; Iyoda. T.; Shimidzu. T. Bull. Chem. SOC. Jpn. 1993, 66, 2054-2060. Nawa, K.; Miyawaki, K.; Imae, I.; Noma, N.; Shirota, Y. J. Mater. Chem.

Kanbara, T.; Yamamoto, T. Macromolecules 1993, 26, 1975-1979. Shen, P. K.; Huang. H. T.; Tseung, A. C. C. J. Electrochem. SOC. 1992, 139, 1840-1845. Yoneyama, H.; Hirao, S.; Kuwabata, S. J. flectrochem. SOC. 1992, 139, 3141-3146. Read, D. C.; Christensen. P. A.; Hamnett, A. J. Electroanal. Chem.

Siekierski, M.; Plocharski, J.; Catellanl, M.; Destri, S. Springer Ser. Solic%State Scl. 1992, 107, 341-345. Leventis, N.; Chung. Y. C. Chem. Mater. 1992, 4, 1415-1422. Bradley, D. D. C. Synth. Met. 1993, 54, 401-415. Karg, S.; Riess, W.; Dyakonov, V.; Schwoerer, M. Synth. Met. 1993, 54, 427-433. Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavetter, F.; Colaneri, N.; Heeger, A. J. Nature 1992, 357, 477-479. Greenham, N. C.; Morattl, S. C.; Bradley, D. D. C.; Friend, R. H.; Holmes, A. 9. Nature 1993, 365, 628-630. Yamamoto, T.; Wakayama, H.; Fukuda, T.; Kanbara, T. J. Phys. Chem.

Xu, 8.; Holdcroft, S. Macromolecules 1993, 26, 4457-4460. Andrieux, C. P.; Audebert, P.; Hapolt, P.; Saveant, J.-M. J. phys. Chem.

Hoier, S. N.; Park, S.-M. J. Electrochem. SOC. 1993, 140, 2454-2463. Raymond, D. E.; Harrison, D. J. J. Electroanal. Chem. 1993, 355, 115- 131. Qiu, Y.J.; Reynolds, J. R. J. Polym. Sci. Part A: Polym. Chem. 1992, 30, 1315. Mendes Viegas, M. F.; Genies, E. M.; Fouletier, M.; Vieil, E. flectrochim. Acta 1992, 37, 513-522. Lukkari, J.; Aianko, M.; Heikkila, L.; Laiho, R.; Kankare, J. Chem. Mater. 1993, 5, 289-296. Tuomala, R.; Ristimaki, S.; Kankare, J. Synth. Met. 1992, 47,217-231. Li, F.; Albery, W. J. €/8ctrochim. Acta 1992, 37, 393-401. Li. F. 6.; Albery, W. J. Langmulr 1992, 8, 1645-1653. Jeon, D.; Kim, J.; Gallagher, M. C.; Willis, R. F. Science 1992, 256, 1662- 1663. Wei, Y.; Tian, J. Macromolecules 1993, 26, 457-463. Genies, E. M.; N d l , P. Synth. Met. 1992, 46, 285-292. Liang, W.; Lei. J.; Martin. C. R. Synth. Met. 1992, 52, 227-239. Kankare, J.; Vuorinen. V.; Alanko, M.; Lukkari, J. J. Chem. SOC., Chem. Commun. 1993, 241-242. Kim, Y.-T.; Yang, H.; Bard, A. J. J. Electrochem. SOC. 1991, 738, L71- L74. Yang, H.; Bard, A. J. J. Nectroanal. Chem. 1992, 339, 423-449. Sabatani, E.; Redondo. A.; Rishpon, J.; Rudge. A,; Rubinstein, I.; Gottesfeld, S. J. Chem. Soc.. Faraday Trans. 1993, 89, 267-294. Michaelson, J. C.; McEvoy, A. J.; Kuramoto, N. React. Polym. 1992, 17, 197-206. Osawa. S.; Ito, M.; Tanaka, K.; Kuwano, J. J, Polym. Scl., Pt. B: Polym. Phys. 1992, 30, 19-24. Osaka, T.; Momma. T.; Kanagawa, H. Chem. Left. 1993, 649-652. Witkowski, A.; Brajther-Toth, A. Anal. Chem. 1992, 64, 635-641. Park, D.-S.; Shlm, Y.-B.; Park, S.-M. J. Electrochem. SOC. 19g3, 140,

Qi, Z.; Pickup. P. G. J. Chem. Soc.. Chem. Commun. 1992,1675-1676. Beck, F.; Oberst, M. J. Appl. Electrochem. 1992, 22, 332-340.

1993, 3, 113-1 14.

1993, 354, 325-329.

1992, 96. 8677-6679.

1991, 95, 10158-10164.

2749-2752.

42QR Analytical Chemistry, Vol. 66, No. 12, June 15, 1994

(F243) Cienles. E. M.; MarchesbHo, M.; Bidan, G. Electrochlm. Acta 1992,37.

(F244) LI, S.; Macosko, C. W.; White, H. S. Sclence 1993. 259, 957-960. (F245) Li, S.; White, H. S. J. Electrochem. Soc. 1993, 740, 2473-2476. (F246) Trlvedi, D. C.; Dhawan, S. K. J. Chem. Mater. 1992, 1091-1096. (F247) Torres, W.; Fox, M. A. Chem. Meter. 1992, 4, 583-588. (F248) Yamamoto, K.; Park, Y. S.; Takeoka, S.; Tsuchida, E. J. Electroanel.

(F249) Park, Y.; Yamamoto. K.; Takeoka, S.; Tsuchida, E. Bull. Chem. SOC.

(F250) Park, Y .6 ; Ohta, T.; Takeoka, S.; Yamamoto, K.; Tsuchida. E. Bull.

(F251) Miller, L. L.; Zhong, C.J.; Kasai, P. J. Am. Chem. Soc. 1983, 115,

(F252) Fabre, B.; Bidan, G.; Fichou, D. J. Chlm. Phys. Phys.-Chlm. Bbl. 1992,

(F253) Mattoso, L. H. C.; Buihoes, L. 0. S. Synth. Met. 1992, 52, 171-181. (F254) Ocon, P.; Herrasti, P. New J. Chem. 1992, 76, 501-504. (F255) Levi. M. D.; Piserevskaya, E. Y.; Moiodkina, E. B.; Daniiov, A. I . J.

(F258) Kobryanskii, V. M.; Arnautov, S. A. Mekromol. Chem. 1992, 193,453-

(F257) Shimura, T.; Funaki, H.; Nishihara, H.; Aramaki, K.; Ohsawa, T.; Yoshino,

(F258) Morita, M.; Komaguchi, K.; Tsutsumi, H.; Matsuda, Y. Electrochim. Acta

(F259) Goklenberg, L. M.; Aeiyach, S.; Lacaze, P. C. J. Electfoanal. Chem.

(F260) Goldenberg, L. M.; Aeiyach, S.; Lacaze, P. C. J. Electroanel. Chem.

(F261) Froyer, 0.; Olilvier, G.; Chevrot, C.; Slove, A. J. Electroanel. Chem.

(F262) Phani, K. L. N.; Pitchumani, S.; Ravichandran, S.; Selvan, S.T.; Bharathey,

(F263) Jehouiet, C.; Obeng, Y. S.; Kim, Y-T.; Zhou, F.; Bard, A. J. J. Am. Chem.

(F264) Koh, W.; Dubois, D.; Kutner, W.; Jones, M. T.; Kadish, K. M. J. Phys.

(F265) Zhou, F.; Yen, S.-L.; Jehoulet, C.; Laude, D. A., Jr.; Guan, 2.; Bard, A.

(F266) Hili, M. G.; Mann, K. R.; Miller, L. L.; Penneau, J.-F. J. Am. Chem. Soc.

(F267) Hill. M. 0.; Penneau, J.-F.; Zinger, B.; Mann, K. R.; Miller, L. L. Chem.

1015-1020.

Chem. 1991, 378, 171-181.

Jpn. 1992, 65, 1860-1865.

Chem. SOC. Jpn. 1993, 66, 2449-2451.

5982-5990.

89, 1053-1062.

Chem. Soc., Chem. Commun. 1992, 149-151.

463.

K. Chem. Lett. 1992, 457-460.

1992. 37, 1093-1099.

1992, 327, 173-184.

1992, 335, 151-161.

1992, 327, 159-171.

S. J. Chem. Soc., Chem. Commun. 1933, 179-161.

SOC. 1992, 114, 4237-4247.

Chem. 1992, 96, 4163-4165.

J. J. Phys. Chem. 1992, 96, 4160-4162.

1992, 114, 2728-2730.

Meter. 1992, 4, 1106-1113. (F268) Bliuerle, P.; Segeibacher, U.; Maier, A.; Mehring, M. J. Am. Chem. Soc.

(F269) Zotti, G.; Schiavon, G.; Berlin, A.; Pagani, G. Chem. Mater. 1993, 5, 1893, 115, 10217-10223.

620-624. (F270) Biiuerie, P.; Segeibacher, U.; Gaudl, K.4.; Hutlenlocher, D.; Mehring.

(F271) Xu, 2.4.; Horowitz, G. J. Elechoanal. Chem. 1992, 335, 123-134. (F272) Quay. J.; Diaz, A.; Wu, R.; Tour, J. M.; Dao, L. H. Chem. Mater. 1992.

(F273) Guay,J.;Kasai.P.;Diaz,A.;Wu,R.;Tour,J.M.;Dao,L.H.Chem.Mater.

(F274) Guay, J.; Dlaz, A.; Wu, R.; Tour, J. M. J. Am. Chem. Soc. 1993, 715.

(F275) Jozefiak, T. H.; Ginsburg, E. J.; Gorman, C. B.; Grubbs, R. H.; Lewis,

(F276) Duffm, G. L.; Pickup, P. G. J. Phys. Chem. 1991, 95, 9634-9635 (F277) Son, Y.; Rajeshwar, K. J. Chem. Soc., Faraday Trans. 1992, 88, 605-

(F278) Van Dyke, L. S.; Kuwabata, S.; Martin, C. R. J. Electrochem. Soc. 1993,

(F279) Hoier, S. N.; Park, S.-M. J. Phys. Chem. 1992, 96, 5188-5193. (F280) Tolbert, L. M. Acc. Chem. Res. 1992, 25, 561-566. (F281) Cain, S. R.; Gale, D. C.; Gaudieiio, J. G. J. Phys. Chem. 1991, 95,

(F282) Vorotyntsev, M. A.; Daikhin, L. I.; Levi, M. D. J. Electroanal. Chem.

(F283) Doblhofer, K. J. Nectroanal. Chem. 1992. 331, 1015-1027. (F284) Mafe, S.; Manzanares, J. A.; Reiss, H. J. Chem. Phys. 1993, 98, 2408-

(F285) Chertier, P.; Mattes, B.; Reiss, H. J. Phys. Chem. 1992, 96,3556-3560. (F286) Asturlas, G. E.; Jang, 0.-W.; MacDiarmid, A. 0.; Doblhofer, K.; Zhong,

(F287) Aoki, K. J. Electroanal. Chem. 1992, 334, 279-290. (F288) Daikhin, L. 1.; Levin, M. D. J. Chem. Soc., Faraday Trans. 1992, 88,

(F289) Bacskai, J.; Kertesz, V.; Inzeit, G. Electrochim. Acta 1993, 38, 393-

(F290) Santhanam, K. S. V.; Gupta, N. Trends Po/ym. Sci. 1993, 1, 284-289. (F291) Novak, P.; Vieistich, W. Collect. Czech. Chem. Commun. 1992, 57,

(F292) Desihrestro, J.; Scheltele, W.: Haas, 0. J. Electroanel. Chem. 1992,

(F293) Velayutham, D.; Noel, M. Talenta 1992, 39, 481-486. (F294) Kostecki, R.; Ulmann, M.; Augustynski, J.; Strike, D. J.; Koudeika-Hep,

(F295) Leone, A.; Marino, W.; Scharifker, B. R. J. Electrochem. SOC. 1992,

(F296) Bose, C. S. C.; Rajeshwar, K. J. Electroanal. Chem. 1992, 333, 235-

M. Angew. Chem., Int. Ed. Engl. 1993, 32, 76-78.

4, 255-258.

1992, 4, 1097-1105.

1869-1874.

N. S. J. Am. Chem. Soc. 1993, 115, 4705-4713.

610.

140, 2754-2759.

9584-9589.

1992, 332, 213-235.

2410.

C. Ber. Bunsenges. Phys. Chem. 1991, 95. 1381-1384.

1023- 1026.

397.

339-348.

739, 2727-2736.

M. J. Phys. Chem. 1993, 97, 8113-8115.

139, 438-443.

256 (F297) Ch&, C. C.; Bose, C. S. C.; Rajeshwar, K. J. Electroanel. Chem. 1993,

(F298) Beck, F.; Dahihaus, M. J. Appl. Electrochem. 1993, 23, 781-789. 350, 161-178.

(F299)

(F300) (F301)

(F302)

(F303) (F304) (F305) (F306)

(F307) (F308) (F309)

(F310)

(F311)

(F312)

(F313) (F314) (F315)

(F316) (F317)

(F318) (F319) (F320)

(F321)

(F322)

(F323) (F324)

(F325)

(F326)

(F327) (F328) (F329) (F330)

(F331) (F332) (F333)

(F334) (F335) (F336)

(F337)

(F338) (F339) (F340)

(F341)

(F342) (F343)

(F344)

(F345) (F348)

(F347)

(F348)

(F349)

(F350)

(F351)

(F352)

(F353)

(F354)

(F355)

(F358)

(F357)

Beck, F.; Dahihaus. M.; Zahedl, N. Electrochim. Acta 1992, 37, 1285- 1272. Lawson, D. R.; Liang, W.; Martin, C. R. Chem. Meter. 1993,5400-402. Fabrizio, M.; Furlanetto, F.; Mengoli, G.; Musiani, M. M.; Paoiucci, F. J. Electroanel. Chem. 1992. 323, 197-212. Otero. T. F.; Angulo, E.; Rodrlquez, J.; Santamaria, C. J. Ektroanal. Chem. 1992, 341, 369-375. Pel, Q.; Inganas. 0. J. Phys. Chem. 1992, 96. 10507-10514. Pel, 0.; Inganas. 0. J. Phys. Chem. 1993, 97, 6034-6041. Herod, T. E.; Schlenoff, J. 8. Chem. Meter. 1993, 5, 951-955. Aoki, K.; Aramoto, T.; Hoshino, Y. J. Electroanal. Chem. 1992, 340.

McCoy, C. H.; Wrighton, M. S. Chem. Meter. 1993, 5, 914-916. Fox, M. A. Acc. Chem. Res. 1992, 25, 569-574. Buck, R. P.; SurrMge, N. A.; Murray, R. W. J. Electrochem. Soc. 1992, 139. 136-144.

127-135.

Han; D.; Shimada, S.; Murray, R. W.; Silve, M. phys. Rev. B. Condens. Matter 1992. 45. 9436-9438. Nishihara, H.; Akasaka, M.; Tateishi, M.; Arameki, K. Chem. Lett. 1992.

Gottesfeid, S.; Uribe. F. A.; Armes. S. P. J. Electrochem. SOC. 1992, 206 1-2064.

139, L14-Ll5. Chin, H.-T.; Lin, J.4. J. Meter. Scl. 1992, 27, 319-327. Smith, C. P.; White, H. S. Anal. Chem. 1992, 64, 2398-2405. Pope, J. M.; Tan, 2.; Kimbrell, S.; Buttry, D. A. J. Am. Chem. Soc. 1992. 114, 10085-10086. DeLong, H. C.; Buttry, D. A. Langmulr 1992, 8, 2491-2496. Kitamura, F.; Ohsaka, T.; Tokuda, K. J. Electroanal. Chem. 1993, 347,

Creager, S. E.; Weber, K. Langmulr 1993, 9, 844-850. Becka, A. M.; Miller, C. J. J. Phys. Chem. 1992, 96, 2657-2668. Takehara, K.; Hiroyuki, T.; Ide, Y. J. Coliohj Interface Scl. 1993, 156,

Finklea, H. 0.; Hansbw, D. D. J. Am. Chem. Soc. 1992, 114,3173- 3181. Curtin, L. s.; Peck, S. R.; Tender, L. M.; Murray, R. W.; Rowe, G. K.; Creager, S. E. Anal. Chem. 1993, 65, 386-392. Hong, HA. ; Mailouk, T. E. Langmulr 1991. 7, 2362-2369. Obeng,Y. S.;Laing,M.E.; Friedli,A.C.;Yang,H.C.; Wang,D.;Thuistrup, E. W.; Bard, A. J.; Michl, J. J. Am. Chem. Soc. 1992, 174, 9943-9952. Finklea, H. 0.; Hanshew, D. D. J. Electroanal. Chem. 1993, 347, 327- 340. Finklea, H. 0.; Ravenscroft, M. S.; Snider, D. A. Langmulr 1993, 9,

Doblhofer, K.; Figura, J.; Fuhrhop, J.-H. Langmuir 1992,8, 161 1-1816. Cheng, Q.; Braher-Toth, A. Anal. Chem. 1992, 64, 1998-2000. Xie, Y.; Dong, S. J. Chem. Soc., Faraday Trans. 1992, 88.2697-2700. Wang, J.; Frostman, L. M.; Ward, M. D. J. Phys. Chem. 1992, 96,

Maiem, F.; Mandier, D. Anal. Chem. 1993, 65, 37-41. Smith, C. P.; White, H. S. Langmulr 1993, 9, 1-3. Redepenning, J.; Tunison, H. M.; Finklea, H. 0. Langmulrl993, 9, 1404- 1407. Acevedo, D.; Abruira, H. D. J. Phys. Chem. 1991, 95, 9590-9594. Rowe, G. K.; Creager, S. E. Langmuir 1991, 7, 2307-2312. Lindholm-Sethson, B.; Orr, J. T.; Ma@, M. Langmulr 1993, 9, 2181- 2167. Charych, D. H.; Goss, C. A.; Majda. M. J. Electroanal. Chem. 1992.323, 339-345. Katz, E.; Itzhak, N.; Willner, I. Langmulr 1993, 9, 1392-1396. Bilewicz, R.; Ma@, M. Langmulr 1991, 7, 2794-2802. Waiczak, M. M.; Popenoe, D. D.; Delnhammer. R. S.; Lamp, B. D.; Chung, C.; Porter, M. D. Langmulr 1991, 7, 2687-2693. Weisshaar, D. E.; Lamp, B. D.; Porter, M. D. J. Am. Chem. Soc. 1982,

Chailapakui. 0.; Crooks, R. M. Langmulr 1993, 9, 884-886. Odashima, K.; Kotato, M.; Sugawara, M.; Umezawa, Y. Anal. Chem. 1993, 65, 927-938. Takehara, K.; Yamada, S.; Ide, Y. J. Electroanal. Chem. 1992, 333, 339-344. Kim. Y. T.; Bard, A. J. Langmulr 1992, 8, 1096-1102. Katz, E.; Rikiin, A.; Willner, I. J. Electroanel. Chem. 1993, 354, 129- 144. Lu, T.; Zhang, L.; Gokei, 0. W.; Kaifer, A. E. J. Am. Chem. SOC. 1993,

37 1-381.

274-278.

223-227.

5224-5228.

114, 5860-5862.

115, 2542-2543. Cammarata, V.; Atanososka, L.; Miller, L. L.; Kolaskie, C. J.; Stailman, B. J. Langmuk 1992, 8, 876-886. Kwan, V. W. S.; Cammarata, V.; Miller, L. L.; HHi, M. 0.; Mann, K. R. Langmulr 1992, 8, 3003-3007. Iwamoto, M.; Majima, Y.; Naruse, H.; Noguchi, T.; Fuwa, H. J. Chem.

Liu, Z.-F.; Hashimoto, K.; Fujishima, A. Chem. Phys. Lett. 1991, 785,

Llu. L F . ; Morigaki, K.; Hashimoto. K.: FuJishima. A. Anal. Chem. 1992, 64, 134-137. Morigaki, K.; Liu, 2. F.; Hashimoto, K.; Fujishima, A. Ber. Bunsenges. Phys. Chem. 1993, 97, 860-864. Liu, Z. F.; Morigaki, K.; Hashimoto, K.; Fujishima, A. J. Photochem. Photobiol. A 1992, 65, 285-292. Song, S.; Clark, R. A.; Bowden, E. F.; Tarlov. M. J. J. Phys. Chem. 1993, 97, 6564-6572. Collinson, M.; Bowden, E. F.; Tarlov, M. J. Langmuk 1892, 8, 1247- 1250. Nakashima,N.;Abe,K.;Hbohashi,T.;Hamada,K.;Kunitake.M.;Manabe. 0. Chem. Lett. 1993. 1021-1024.

PhyS. 1991, 95, 8561-8567.

501-504.


(F358) Erabi, T.; Ozawa, S.; Hayase, S.; Wada, M. Chem. Lett. 1992, 2115-

(F359) Kinnear, K. T.; Monbouquette, H. G. Langmuir 1993, 9, 2255-2257. (F360) Parpaleix, T.; Laval, J. M.; Majda, M.; Bourdlllon, C. Anal. Chem. 1992,

(F361) Wlllner, I.; Katz, E.; Riklln, A.; Kasher. R. J. Am. Chem. SOC. 1992, 114,

(F362) Sato, Y.; Itoigawa, H.; Uosaki, K. Bull. Chem. SOC. Jpn. 1993, 66,

(F363) Martin, A. S.; Sambies, J. R.; Ashwell, G. J. Phys. Rev. Lett. 1993, 70,

(F364) Ueyama, S.; Wada, 0.; Miyamoto, M.; Kawakubo, H.; Inatomi, K.; Isoda,

(F365) Liu, M. D.; Leaner, C. R.; Facci, J. S. J. Phys. Chem. 1992, 96, 2804-

(F366) Sucheta, A.; uI Haque, I.; Rusling, J. F. Langmuir1992, 8, 1633-1636. (F367) Nelson, A. J. Chem. SOC., Faraay Trans. 1993, 89, 3081-3090. (F368) Abbott, A. P.; Gounili, G.; Bobbltt, J. M.; Rusiing, J. F.; Kumosinskl. T.

(F369) Li. J.; Kaifer, A. E. Langmuir 1993, 9, 591-596. (F370) (F371) Petty, M.; Lovett, D. R.; Miller, J.; Silver, J. J. Mater. Chem. 1991, 1,

(F372) Engelman, E. E.; Evans, D. H. Langmuir 1992, 8, 1637-1644. (F373) Becka, A. M.; Miller, C. J. J. Phys. Chem. 1993, 97, 6233-6239. (F374) Rillema, D. P.; Edwards, A. K.; Perine. S. C.; Crumbliss, A. L. Inorg.

(F375) Dvorak, 0.; DeArmond, M. K. J. Phys. Chem. 1993, 97, 2646-2648. (F376) Iroh, J. 0.; Bell, J. P.; Scola, D. A. J. Appl. Polym. Sci. 1991, 43,

(F377) Osada, Y.; Okuzaki, H.; Hori, H. Nature 1992, 355, 242-244. (F378) Wang, J.; Golden, T.; Lin, Y.; Angnes, L. J. Electroanal. Chem. 1992,

(F379) Christie, I. M.; Treloar, P. H., Vadgama, P. Anal. Cbim. Acta 1992,269,

21 18.

64, 641-646.

10965- 10966.

1032- 1037.

218.

S. J. Eiectroanal. Chem. 1993, 347, 443-449.

2811.

F. J. Phys. Chem. 1992, 96, 11091-11095.

971-976.

Chem. 1991, 30, 4421-4425.

2237-2247.

333, 65-75.

65-73.

G. BIOELECTROCHEMISTRY

Smyth, W. F. Voltammetrlc Determination of Molecules of Biologibal Significance; John Wiley & Sons: England, 1992. Schultz, F. A., Taniguchi, I., Eds. Redox Mechanisms and Interfacial Properties of Molecules of Bioioglcai Importance, Proceedings; The Electrochemical Society: Pennlngton, NJ, 1993; Vol. 93-1 1. Paulsen, K. E.; Stankovich, M. T.; Orville, A.M. MethodsEnzymol. 1993,

Armstrong, F. A.; Butt, J. N.; Sucheta, A. MethodsEnzymol. 1993, 227,

Hill, H. A. 0.; Hunt, N. I. Methods Enzymoi. 1093, 227, 501-521. Cox, J. A.; Przyjazny, A. TrAC, Trends Anal. Chem. 1992, 71,298-302. Ewing, A. G.; Strein, T. G.; Lau, Y. Y. Acc. Chem. Res.1992, 25, 440- 447. Kauffmann, J. M.; Vir& J. C. Anal. Chim. Acta 1993, 273, 329-334. Voik, K. J.; Yost, R. A.; Brajtertoth, A. Anal. Chem. 1992, 64. A21. Ikeda, T. Bull. Electrochem. 1992, 8, 145-159. Bourdillon, C. Ann. N.Y. Acad. Sci. 1992, 672, 195-212. Gorton, L.; Jonsson-Pettersson, G.; Csoregl, E.; Johansson, K.; Dominguez, E.; Markovarga, G. Analyst 1992, 117, 1235-1241. Heller, A. J. Phys. Chem. 1992, 96, 3579-3587. Boguslavsky, L.; Hale, P. D.; Geng, L.; Skothelm, T. A,; Lee, H. S. Solid State Ionics 1993, 60, 189-197. Wilson, R.; Turner, A. P. F. Biosens. Bimlectron. 1992, 7, 165-185. Ivnitskii, D, M.; Kurochkln, I. N.; Varfolomeev, S. D. 2. Anal. Khim. 1991, 26, 1462-1479. HildRch, P. I.; Green, M. J. Analyst 1991. 116, 1217-1220. Turner, A. P. F., Ed. Advances in Biosensors; 1992; Vol. 2. Nakamura, M., Kasahara, Y., Rechnitz, G. A., Eds. Immunochemical Assays and Biosensor Technology for the 1 9 9 0 ~ ~ Part I I I ; Amerlcan Society for Microbiology: Washington, DC, 1992. Wring, S. A.; Hart, J. P. Analyst 1992, 117, 1215-1229. Nikolells, D. P.; Krull, U. J. Electroanalysis 1993, 5, 539-545. Onova-Leitmannova, A.; Tien, H. T. Prog. Surf. Sci. 1992,4 1,337-445. Kuhr, W. G.; Barren, V. L.; Gagnon, M. R.; Hopper, P.; Pantano, P. Anal. Chem. 1993, 65, 617-622. Hale, P. D.; Lee, H. S.; Okamoto, Y. Anal. Lett. 1993, 26, 1073-1085. Kashlwagl, Y.; Osa, T. Chem. Lett. 1993, 677-680. Somasundrum, M.; Bannister, J. V. J. Chem. Soc., Chem. Commun. 1993, 1629-1631. Ohsaka, T.; Tanaka, K.; Tokuda, K. J. Chem. SOC., Chem. Commun. 1903, 222-224. Beley, M.; Collin. J. P. J. Mol. Catal. 1993, 79, 133-140. Shimizu, Y.; Kitani, A.; Ito. S.; Sasaki, K. Denki Kagaku 1993, 61,

Cantet, J.; Bergei, A.; Comtat, M.; Seris, J. L. J. Mol. Catal. 1992, 73,

Xu. H. T.: Kltamura. F.: Ohsaka. T.: Tokuda. K. Denk; Kaoaku 1992.

227, 396-411.

479-500.

872-873.

371-380. . . . .

60; 1068-1074. Allred, C. D.; Mccreery, R. L. Anal. Chem. 1992, 64, 444-448. Matysik, F. M.; Nagy, G.; Pungor, E. Anal. Chlm. Acta 1992,264. 177- 184.

-

Malem, F.; Mandler, D. Anal. Chem. 1993, 65, 37-41. Vandeberg, P. J.; Johnson, D. C. Anal. Chem. 1993, 65, 2713-2718. Lacourse, W. R.; Johnson, D. C. Anal. Chem. 1993, 65, 50-55. Zhou. J. X.; Wang, E. J. Electroanel. Chem. 1992, 337, 1029-1043. Wang, E.; Liu, A. J. Electroanal. Chem 1991, 319, 217-225. (a) Zhao, S. S.; Lennox, R. E. J. Eiectroanal. Chem. 1993, 346, 161- 173. (b) Korell, U.; Lennox, R. B. Anal. Chem. 1992, 64, 147-151.

(G40) Zhao, S. S.; Lennox, P. B. J. Electroanel. Chem. 1993, 346, 161-173. (G41) Tsai, H.; Weber, S. G. Anal. Chem. 1992, 64, 2897-2903. (G42) Malinski, T.; Taha, 2. Nature 1992, 358. 676-678. (G43) Nakamura, N.; Kohzuma, T.; Suzuki, S. Bull. Chem. Soc. Jpn. 1993,

(G44) Nlu, J.; Dong, S. Electroanalysis 1093, 5, 571-574. (G45) Sagara, T.; Takagl, S.; Niki, K. J. Electroanel. Chem. 1993, 349, 159-

171. (G46) Emons, H.; Wittstock, G.; Vo!gt, 6.; Seidel, H. Fresenius J. Anal. Chem.

1992, 342, 737-739. (G47) Vehagen, M. F. J. M.; Hagen, W. R. J. Electroanal. Chem. 1992,334,

339-350. (G48) Takehara, K.; Takemura, H.; Ide, Y. J. ColloM InterfaceSci. 1993, 156,

274-278.

66, 1289-1291.

Nakashima, N.; Masuyama, K.; MochMa, M.; Kunkake, M.; Manabe, 0. J. Electroanal. Chem. 1991, 379, 355-359. Mallik, 6.; Gani, D. J. Electroanal. Chem. 1992, 326, 37-49. Sagara, T.; Murakami, H.; Igarashi, S.; Sato, H.; Niki, K. Langmulr 1991. 7, 3190-3196. Wlide, C. P.; Ding, T. J. Electroanel. Chem. 1992, 327, 279-290. Zhou, C. L.; Ye, S. Y.; Klm, J. H.; Cotton, T. M.; Yu, X. J.; Lu, T. H.; Dong, S. J. J. Electroanal. Chem. 1991, 379, 71-83. Szucs, A.; HRchens, G. D.; Bockris, J. 0. M. Electrochim. Acta 1992,

Mayne, A. J.; Cataidi, T. R. 1.; Knaii, J.; Avery, A. R.; Jones, T. S.; Plnhelro, L.; Hill, H. A. 0.; Brlggs, G. A. D.; Pethlca, J. 6.; Weinberg, W. H. Faraday Discuss. 1992, 199-212. Tominaga, M.; Hayashi, K.; Taniguchi, I. Anal. Sci. 1992, 8, 829-836. Haladjian, J.; Bruschi, M.; Nunzl, F.; Bianco, P. J. Necfroanal. Chem.

Bond, A. M.; Hill, H. A. 0.; Komorskyiovric, S.; Lovrlc, M.; Mccarthy, M. E.; Psalti, J. S. M.; Walton, N. J. J. Phys. Chem. 1992, 96, 8100- 8105. Nakashima, N.; Abe, K.; Hirohashl, T.; Hamada, K.; Kunkake, M.; Manabe, 0. Chem. Lett. 1993, 1021-1024. Salamon, 2.; Gleason, F. K.; Tollln, G. Arch. Blochem. Blophys. 1992, 299, 193-198. Taniguchi, I.; Kurihara, H.; Yoshida, K.; Tominaga, M.; Hawkrage, F. M. Denki Kagaku 1992, 60, 1043-1049. Daido, T.; Akalke, T. J. Electroanal. Chem. 1093, 344, 91-106. Taniguchi, 1.; Hayashi, K.; Tominaga, M.; Muraguchi, R.; Hlrose, A. Denki Kagaku 1993, 61, 774-775. Colllnson, M.; Bowden, E. F. Langmuir 1992, 8, 2552-2559. Ohtani, M.; Ikeda, 0. J. Elecfroanal. Chem. 1993, 354, 311-317. Dana, D.; Hill, H. A. 0.; Nakayama, H. J. Electroanai. Chem. 1992,324,

Buchi, F. N.; Bond, A. M.; Codd, R.; Huq, L. N.; Freeman, H. C. Inorg. Chem. 1992, 37, 5007-5014. Yuan, X.; Hawkridge. F. M.; Chlebowski, J. F. J. Electroanal. Chem.

37, 403-412.

1993, 352, 329-335.

307-323.

1993, 350, 29-42; Barker, P. D.; Mauk, A. G. J. Am. Chem. Soc. 1902, 114,3619-3624. Bixler, J.; Bakker, G.; McLendon, G. J. Am. Chem. SOC. 1992, 114, 6938-6939. Hilgen-Willis, S.; Bowden, E. F.; Pieiak, G. J. J. Inorg. Biochem. 1993, 51. 649-653. . . , . . - -.

Cruanes, M. T.; Rodgers, K. K.; Sligar, S. G. J. Am. Chem. SOC. 1992, 174. 9660-9661. Kohzuma, T.; Takase, S.; Shidara, S.; Suzuki, S. Chem. Lett. 1993,

Iwasakl, Y.; Suzuki, M.; Takeuchi, T.; Tamiya, E.; Karube, I.; Nishlyama, M.; Horlnouchl, S.; Beppu, T.; Kadoi, H.; Uchiyama. S.; Suzuki, S. Electroanalysis 1992, 4, 765-770. Erabi. T.; Ozawa, S.; Hayase, S.; Wada, M. Chem. Lett. 1992, 21 15- 21 16. Moreno, C.; Costa, C.; Moura, I.; Legail, J.; Liu, M. Y.; Payne, W. J.; Vandijk, C.; Moura, J. J. G. Eur. J. Blochem. 1093, 272, 79-86. Iwasaki, Y.; Takeuchi, T.; Tamiya, E.; Karube, I.; Nishlyama, M.; Horinouchi, S.; Beppu, T.; Kadoi, H.; Uchiyama, S.; Suzuki, S.; Suzuki, M. .Electroanalysis 1992, 4, 771-776. Moreno, C.; Franco, R.; Moura, I.; Legall, J.; Moura, J. J. G. Eur. J. Biochem. 1993, 277, 981-989. Butt, J. N.; Sucheta, A.; Armstrong, F. A.; Breton, J.; Thomson, A. J.; Hatchikian, E. C. J. Am. Chem. Soc. 1993, 115, 1413-1421. (a) Song, S.; Clark, R. A,; Bowden, E. F.; Tarlov, M. J. J. Phys. Chem. 1993, 97, 6564-6572. (b) Bartlett, P. N.; Carwna, D. J. Analyst 1992,

Collinson, M.; Bowden, E. F.; Tarlov, M. J. Langmulr 1992, 8, 1247-

149-152.

117, 1287-1292.

1250 _. .

Cooper, J. M.; Greenough, K. R.; McNell. C. J. J. Electroanal. Chem. 1993. 347. 267-275. Reeves, J. H.; Song, S.; Bowden, E. F. Anal. Chem. 1993, 65,683-688. Ueyama, S.; Wada, 0.; Mlyamoto, M.; Kawakubo, H.; Inatomi, K.; Isoda, S. J. Electroanal. Chem. 1993, 347, 443-449. Niwa, M.; Fukui, H.; Higashi, N. Macromolecules 1993,26,5816-5818. Hobara, D.; Niki, K.; Cotton, T. M. DenkiKagaku 1993. 67, 776-777. Coilinson, M.; Bowden, E. F. Anal. Chem. 1902. 64, 1470-1476. Schlereth, D. D.; Mantele, W. Biochem/stry 1903, 32, 11 18-1 126. Schlereth, D. D.; Fernandez, V. M.; Manteie, W. Biochem/stry1993,32, 9199-9208. Tominaga, M.; Kumagai, T.; Takita, S.; Taniguchi, I . Chem. Lett. 1993, 1771-1774. Taniguchl, I.; Watanabe, K.; Tominaga, M.; Hawkridge, F. M. J. EleCtfoanal. Chem. 1992, 333, 331-338. King, B. C.; Hawkridge, F. M.; Hoffman, B. M. J. Am. Chem. SOC. 1992, 714, 10603-10608.


Detrich, J. L.; Erb, G. A.; Beres, D. A.; Rlckard, L. H. I n Charge and FWEffects In Bbsystems-3; Allen, M. J., Cleary, S. F., Sowers, A. E., Shillady, D. D., Eds.; Birkhauser: Boston, 1992 pp 41-52. Ohno, H.; Tsukuda, T. J. Electroanal. Chem, 1992, 347, 137-149. Dong, S. J.; Chu, Q. H. Electroanalysk 1993, 5, 135-140. Zhou, J. X.; Wang, E. Electrochlm. Acta 1992, 37, 595-602. Cullison, J. K.; Hawkridge, F. M.; Nakashlma, N.; Hartzell, C. R. I n Charge and Field Effects In Blosystems-3; Alien, M. J., Clary, S. F., Sowers, A. E., Shillady, D. D., Eds.; Blrkhauser: Boston, 1992; pp

Salamon, 2.; Hazzard, J. T.; Tollln, 0. Roc. Natl. Acad. Scl. U.S.A.

Sucheta, A.; Ackrell, 8. A. C.; Cochran, 8.; Armstrong, F. A. Nature 1992, 356, 361-382. Sucheta. A.; Cammack, R.; Weiner, J.; Armstrong, F. A. Blochemlstty

29-40.

1993, 90, 6420-8423.

. . 1993, 32, 5455-5465.

(G101) Kinnear, K. T.; Monbouquette, H. G. Langmulr 1993, 9, 2255-2257. (G102) Klnnear, K. T.; Monbouquette, H. 0. Blotechnol. Bloeng. 1993,42,140-

1 A A (G103) Bknco, P.; Haladjian, J. J. Electrochem. SOC. 1992, 739, 2428-2432. (0104) Nlkandrov, V. V.; Arlstarkhov, A. I.; Shlyk, M. A.; Krasnovskli, A. A.

Dokl. Akad. Nauk USSR 1991, 319, 151-154. (0105) Azab, H. A.; Bancl, L.; Borsarl, M.; Luchlnat, C.; Sola, M.; Viezzoli, M.

S. Inorg. Chem. 1992, 37, 4649-4655. (G106) Borsarl, M.; Azab, H. A. Bloelectrochem. Bhnerg. 1992,27,229-233. (G107) Shlnohara, H. Denki Kagaku 1993, 67, 780-782. (0108) Zhao, J. G.; Henkens, R. W.; Stonehuerner, J.; Waly, J. P.; Crumbllss,

A. L. J. Electroanal. Chem. 1992, 327, 109-119. (G109) Ikeda, T.; Mlyaoka, S.; Matsushita, F.; Kobayashi, D.; Senda, M. Chem.

Lett. 1992. 847-850. (G110) Fiores, J. R.; Ahrarez, J. M. F. Electroanalysls 1992, 4, 347-354. (G111) Leonhard, M.; Mantele, W. Biochemistry 1993, 32, 4532-4538. (G112) Bauscher, M.; Leonhard, M.; Moss, D. A.; Mantele, W. Blochlm. Blophys. . . . .

Acta 1993, 7783, 59-71.

M. T. Bbchemlstty 1992, 37, 11755-11761.

Chlm. Blol. 1993, 90, 11 13-1 135.

Jpn. 1992, 65, 424-429.

(01 13) Pauisen, K. E.; Orvllb, A. M.; Frerman, F. E.;Lipscomb, J. D.; Stankovlch,

(0114) Durliat, H.; Courteix, A.; Bergel, A,; Comtat, M. J. Chlm. phys., Phys.-

(G115) Coury, L. A.; Liu, Y.; Murray, R. W. Anal. Chem. 1993, 65, 242-246. (Gll6) Sagara, T.; Kolde, T.; Saito, H.; Akutsu, H.; Niki, K. Bull. Chem. SOC.

(G117) Randrlamahazaka, H.; Nigretto, J. M. Anal. Chlm. Acta 1992, 257, 247-256.

(G118) Randrlamahazaka, H. N.; Nlgretto, J. M. Electroanalysis 1993, 5. 231- 241.

(0119) Roscoe, S. G.; Fuller, K. L.; Robitallle, G. J. Colloid Interface Scl. 1993, 760, 243-251.

(G120) Relpa, V.; Gaigaias, A.; Abramowitz, S. J. Electroanal. Chem. 1993, 348, 413-428.

(G121) Asanov, A. N.; Larina, L. L. I n ChargeandFle~EtfectsinBiosystems-3 Allen, M. J., Cleary, S. F., Sowers, A. E., ShiHady, D. D., Eds.; Birkhauser: Boston, 1992; pp 13-28.

(G122) Katz, E. Y.; Solovev, A. A. Anal. Chlm. Acta 1992. 266, 97-106. (0123) Solovev, A. A.; Katz, E. Y.; Shuvalov, V. A.; Erokhln, Y. E. Sov.

Electrochem. 1992, 28, 1448-1456. (G124) Cai, R.; Baba, R.; Hashimoto, K.; Kubota, Y.; Fujlshlma, A. J. Electroanal.

Chem. 1993, 360, 237-245. (G125) Agostlano, A.; Goetze, D. C.; Carpentler, R. Electrochlm. Acta 1993,

(G126) Janata, J. Anal. Chem.. review in this issue, (G127) Anderson, D. J.; Van Lente, F. Anal. Chem. 1993, 65, 364R-484R. (G128) Hecht, H. J.; Kalisz, H. M.; Hendle, J.; Schmld, R. D.; Schomburg, D.

(G129) Reach, G.; Wilson, G. S. Anal. Chem. 1992, 64. 381A-386A. (G130) Albery, W. J.; Bartlett, P. N.; Drlscoll, B. J.; Lennox, R. B. J. Electroanal.

(G131) Albery, W. J.; Kalia, Y. N.; Magner, E. J. Electroanal. Chem. 1992,325,

(G132) Sorochinskll, V. V.; Kurganov, B. I. Sov. Electrochem. 1992, 28, 153-

(GI331 Marcheslello, M.; Genies, E. J. Ektroanal. Chem. 1993, 358, 35-48. (G134) Tatsuma, T.; Watanabe, T. Anal. Chem. 1993. 65, 3129-3133. (G135) Bacha, S.; Bergel, A.; Comtat, M. J. Electroanal. Chem. 1993, 359,

(0136) Battagiinl, F.; Calvo, E. J. Anal. Chlm. Acta 1992, 258, 151-160. (G137) Randrlamahazaka, H.; Nigretto, J. M. Electroanalysis 1993, 5, 221-

(G138) Uhegbu, C. E.; Lim, K. B.; Pardue, H. L. Anal. Chem. 1993, 65, 2443-

(G139) Uhegbu, C. E.; Pardue, H. L.; Love, M. D.; Toosi, S. Anal. Chlm. Acta

(G140) Lyons, M. E. G.; Lyons, C. H.; Mlchas, A,; Bartlett, P. N. Analyst 1992,

((3141) Tatsuma, T.; Watanabe, T.; Okawa, Y. Anel. Chem. 1992. 64, 830-

(G142) Tatsuma, T.; Watanabe, T. Anal. Chem. 1092, 64, 625-630. (G143) Badia, A.; Carllnl, R.; Fernandez, A,; Battaglinl, F.; Mlkkelsen, S. R.;

(G144) Bourdillon, C.; Demallle, C.; Moiroux, J.; Saveant, J. M. J. Am. Chem.

(G145) Kajiya, Y.; Yoneyama, H. J. Electroanal. Chem. 1992, 328, 259-269. (0146) Kajlya, Y.; Yoneyama, H. J. Electroanal. Chem. 1992, 347, 85-92. (0147) Aokl. A.; Helier, A. J. Phys. Chem. 1993, 97, 11014-11019. (G148) Vreeke, M.; MaMan, R.; Heller, A. Anal. Chem. 1992, 64,3084-3090. (G149) Katakis. I.; Heller, A. Anal. Chem. 1992, 64, 1008-1013.

38, 757-762.

J. Mol. Blol. 1993, 229, 153-172.

Chem. 1992, 323, 77-102.

83-93.

157.

21-38.

230.

2451.

1993, 287, 549-555.

777, 1271-1280.

835.

Engllsh, A. M. J. Am. Chem. SOC. 1993, 715, 7053-7060.

SOC. 1993, 715, 2-10.

(G150) Ye, L.; Himmerle, M.; Olsthoorn, A. J. J.; Schuhmann. W.; Schmidt, H.-L.; Duine. J. A.; Heller, A. Anal. Chem. 1993, 65, 238-241.

(0151) Ohara, T. J.; Vreeke, M. S.; Battagllni, F.; Heller. A. Electroanalysis

(G152) Gargullo, M. G.; Huynh, N.; Proctor, A.; Mlchael. A. C. Anal. Chem.

(G153) Dressman, S. F.; Gargullo, M. 0.; Sullenberger, E. F.; Michael, A. C. J.

(G154) Iljima, S.; Mizutani, F.; Yabukl, S.; Tanaka. Y.; Asai, M.; Katsura. T.;

(G155) Hendry, S. P.; Cardosi, M. F.; Turner, A. P. F.; Neuse, E. W. Anal. Chim.

(G156) Hale, P. D.; Lee, H. S.; Okamoto, Y. Anal. Lett. 1993, 26, 1-16. (G157) Cahro, E. J.; Danilowlcz, C.; Dlaz, L. J. Chem. Soc., Faraday Trans.

(G158) Chen. C. J.; Liu. C. C.; Savlnell, R. F. J. Electroanel. Chem. 1993, 348.

(G159) Lee, H. S.; Llu. L. F.; Hale, P. D.; Okamoto, Y. Hetemat. Chem. 1992.

(G180) Arai, 0.; Masuda, M.; Yasumori, I. Chem. Lett. 1992, 1791-1794. (G161) BBlanger, D.; Nadreau, J.; Fortler, 0. Electroanalysk 1992,4,933-940. (G162) Cooper, J. M.; Bloor, D. Electroanalysk 1993, 5, 883-886. (Gl63) Caselli, M.; Dekmonica. M.; Portaccl, M. J. Electroanal. Chem. 1991,

(G164) Tatsuma, T.; Gondaira, M.; Watanabe, T. Anal. Chem. 1992,64,1183-

(G165) Tatsuma, T.; Watanabe, T.; Watanabe, T. J. Electroanel. Chem. 1993,

(0166) Bartlett, P. N.; Ali, 2.; Eastwickfield, V. J. Chem. Soc., Farady Trans.

(G167) KaJlya, Y.; Matsumoto, H.; Yoneyama, H. J. Electroanal. Chem. 1991,

1993, 5. 825-831.

1993, 65, 523-528.

Am. 0". Soc. 1993, 175, 7541-7542.

Hosaka, S.; Ibonai, M. Anal. Chlm. Acta 1993, 287, 483-487.

Acta 1993, 287, 453-459.

1993, 89, 377-364.

3 17-338.

3, 303-310.

319, 361-364.

1187.

356, 245-253.

1992, 88, 2677-2683.

319. 185-194. ., .. (G168) Khan, G. F.; Kobatake, E.; Ikarlyama, Y.; Aizawa, M. Anal. Chlm. Acta

1993. 287. 527-533. (Gl69) Begum, A.; Kobatake, E.; Suzawa, T.; Ikarlyama, Y.; Alzawa, M. Anal.

(G170) Sun, 2. S.; Tachikawa, H. Anal. Chem. 1992, 64. 1112-1117. (G171) Lyons, M. E. G.; Lyons, C. H.; Fitzgerald, C.; Bannon. T. Analyst1993,

(G172) Cooper, J. C.; Hail, E. A. H. €lectroanalysk 1993, 5, 385-397. (G173) Haruyama, T.; Shlnohara, H.; Ikarlyama, Y.; Alzawa. M. J. Electroanal.

(G174) Sadlk, 0. A.; Wallace, 0. 0. Anal. Chim. Acta 1993, 279, 209-212. (0175) Wolowacz, S. E.; Hin, B. F. Y. Y.; Lowe, C. R. Anal. Chem. 1992, 64,

(0176) Yonhln. B. F. Y.; Smolander. M.; Crompton, T.; Lowe, C. R. Anal. Chem.

Chlm. Acta 1993, 280, 31-36.

778, 361-369.

Chem. 1993, 347, 293-301.

154 1 - 1545.

1993, 65, 2067-2071. (G177) Cosnler, S.; Innocent, C. J. Elechoanal. Chem. 1992, 328, 361-366. (G178) Cocheguerente, L.; Cosnier, S.; Innocent, C.; Maiiley, P.; Moutet, J. C.;

Morelis, R. M.; Leca, B.; Coubt, P. R. Electroanalysls 1993,5,647-652. (G179) Wang, L.; Kobatake, E.; Ikariyama, Y.; Alzawa, M. DenklKagaku 1992,

60, 1050-1055. (G180) Koopel, C. G. J.; DeruRer, 8.; Nolte, R. J. M. J. Chem. Soc., Chem.

(G181) Khan, 0. F.; Kobatake, E.; Shinohara, H.; Ikarlyama, Y.; Aizawa, M.

(G182) Nlshlzawa, M.; Matsue, T.; Uchida, I. Anal. Chem. 1992, 64, 2642-

(G183) Hoa, D. T.; Kumar, T. N. S.; Punekar. N. S.; Srlnivasa, R. S.; Lal, R.; Contractor, A. Q. Anal. Chem. 1992, 64, 2645-2646.

(G184) Bartlett, P. N.; Birkln, P. R. Anal. Chem. 1993, 65, 1118-1119. (G185) Maldan, R.; Heller, A. Anal. Chem. 1992, 64, 2889-2896. (G186) Christie, I. M.; Treioar, P. H.; Vadgama, P. Anal. Chlm. Acta 1992,269.

Common. 1991, 1691-1692.

Anal. Chem. 1992, 64, 1254-1258.

2644.

k6-79 -- .-. (G187) Lowry, J. P.; O'Nelll, R. D. J. Electroanal. Chem. 1992, 334, 183-194. (G188) Centonze, D.; Guerrlerl. A,; Malltesta, C.; Palmlsano, F.; Zambonin, P.

(G189) Lowry, J. P.; ONeIll, R. D. Anal. Chem. 1992, 64, 453-456. (G190) Palmisano, F.; Zambonln, P. G. Anal. Chem. 1993, 65, 2690-2692. (G191) Chrlstle, I. M.; Vadgama, P.; Lloyd. S. Anal. Chim. Acta 1993, 274,

(G192) Bartlett, P. N.; Tebbutt, P.; Tyrrell. C. H. Anal. Chem. 1992, 64, 138-

(G193) Mlzutanl, F.; Yabuki, S.; Katsura, T. Anal. Chlm. Acta 1993,274, 201-

(G194) Fortler, G.; Valllancourt, M.; Belanger, D. Electroanalysis 1992. 4, 275-

((3195) Wang, J.; Lln, Y. H.; Chen, Q. Electroanalysis 1993, 5, 23-28. (G198) Wang, J.; Lin, Y. H.; Eremenko, A. V.; Ghlndllis. A. L.; Kurochkin, I. N.

(G197) Scott, D. L.; Paddock, R. M.; Bowden, E. F. J. Electroanel. Chem. 1992,

(G198) Armstrong, F. A.; Bond, A. M.; Buchl, F. N.; Hamnett, A.; HIII, H. A. 0.; Lannon, A. M.; Lettlngton, 0. C.; Zoskl, C. G. Analyst 1993, 778,973-

(GI99 Ho, W. 0.; Athey, D.; Mcneli, C. J.; Hager, H. J.; Evans, G. P.; Mullen, W. H. J. Electroanal. Chem. 1993, 351, 185-197.

(G200) Kulys, J.; Bllitewski, U.; Schmid, R. D. Bbelectrochem. Bbenerg. 1991,

(G201) Tatsuma, T.; Watanabe, T. Anal. Chem. 1992, 64, 143-147. (G202) Kobayashi, D.; Ozawa, S.; Mihara, T.; Ikeda. T. h n k l Kagaku 1992,

(0203) Bourdillon, C.; Delamar, M.; Demallle. C.; Hltmi. R.; Molroux, J.; Pinson,

G. Fresenlus J. Anal. Chem. 1992, 342, 729-733.

191-199.

142.

207.

283.

Anal. Lett. 1993, 26, 197-207.

347, 307-321.

978.

26, 277-288.

60, 1056-1062.

J. J. Electroanel. Chem. 1992. 336. 113-123.

10965-10966. (G204) Wlllner, I.; Katz, E.; Rlklln, A.; Kasher, R. J. Am. Chem. Soc. 1992, 714,


(G205) Katz, E.; Riklin, A.; Willner, I. J. Electroanal. Chem. 1993, 354, 129-

(G206) SneJdarkova, M.; Rehak. M.; Otto, M. Anal. Chem. 1993,65.665-668. (G207) Lee, Y. W.; Reed-Mundell, J.; Sukenlk, C. N.; Zull, J. E. Langmulr 1993,

(G208) Amador, S. M.; Pachence, J. M.; Flschetti, R.; McCauiey, J. P.; Smith,

(G209) Hong, H.-G.; Bohn, P. W.; Sligar, S. G. Anal. Chem. 1993, 65, 1635-

(G210) Lbpez, G. P.; Biebuyck. H. A.; l-lirter, R.; Kumar. A.; WhitesMes, G. M.

(G211) Parpaleix, T.; Laval, J. M.; Majda, M.; Bourdillon, C. Anal. Chem. 1992,

(G212) Dicks, J. M.; Cardosi, M. F.; Turner, A. P. F.; Karube, I. Electroanalysis

(G213) Wollenberger, U.; Wang, J.; Ozsoz, M.; Gonzalez-Romero, E.; Scheller,

(G214) Wang, J.; Gonzalezromero, E.; Ozsoz, M. Electroanalysis 1992,4539-

(G215) Wang, J.; Romero, E. 0.; Revielo, A. J. J. Electroanal. Chem. 1993,

(G216) Wang, J.; Revbjo, A. J.; Angnes, L. Electroanalysis 1993, 5, 575-579. (G217) Mlzutani, F.; Yabuki, S.; Katsura, T. Denkl Kagaku 1992, 60, 1141-

(G218) Kulys, J.; Wang, L. 2.; Daugvilaiite, N. Anal. Chim. Acta 1992, 265,

(G219) Kulys, J.; Wang, L. 2.; Maksimovlene, A. Anal. Chim. Acta 1993, 274,

144.

9, 3009-3014.

A. B., 111; Blasle, J. K. Langmulr 1993, 9, 812-817.

1638.

J. Am. Chem. Soc. 1993, 775, 10774-10781.

64, 641-646.

1993, 5, 1-9.

F. Bioelectrochem. Bioenerg. 1991, 26, 287-296.

544.

353, 113-120.

1142.

15-20.

53-58. .. ..

(G220) Kuiys, J.; Glelxner, G.; Schuhmann, W.; Schmldt, H. L. Electroanalysis 1993. 5. 201-207.

(G221) Kulys; J.; Wang, L. 2.; Razumas, V. Electroanalysis 1992, 4, 527-532. (G222) Smlt, M. H.; Rechnitz, G. A. Electroanalysis 1993, 5, 747-751. (G223) Amine, A.; Kauffmann, J. M.; Guilbauit, G. G.; Bacha, S. Anal. Lett.

(G224) Rosenmargalit, 1.; Bettelhelm, A.; Rishpon, J. Anal. Chlm. Acta 1993,

(G225) Pantano, P.; Kuhr, W. G. Anal. Chem. 1993, 65, 623-630. (G226) Csoregi, E.; Gorton, L.; Markovarga, G. Anal. Chlm. Acta 1993, 273,

(G227) Pariente, F.; Hernandez, L.; Abruna, H. D.; Lorenzo, E. Anal. Chim. Acta

(G228) Wang, D. L.; Heller, A. Anal. Chem. 1993, 65, 1069-1073. (G229) Kawagoe, J. L.; Nlehaus, D. E.; Wightman, R. M. Anal. Chem. 1991,

(G230) Wang, J.; Angnes, L. Anal. Chem. 1992, 64, 456-459. (G231) Wang, J.; Naser, N.; Renschler, C. L. Anal. Lett. 1993, 26, 1333-1346. (G232) Yokoyama, K.; Nakajima, K.; Uchyama, S.; Suzuki, S.; Suzuki, M.;

Takeuchi, T.; Tamiya, E.; Karube, I. Electroanalysls 1992, 4,859-864. (G233) Abe, T.; Lau, Y. Y.; Ewing, A. G. Anal. Chem. 1992, 64, 2160-2163. (G234) Motonaka, J.; Faulkner, L. R. Anal. Chem. 1993, 65, 3258-3261. (G235) Bartlett, P. N.; Caruana, D. J. Analyst 1992, 777, 1287-1292. (G236) Zhang, Y.; Wilson, G. S. J. Electroanal. Chem. 1993, 345, 253-271. (G237) Zhao, S.; Korell, U.; Cuccia, L.; Lennox, R. B. J. Phys. Chem. 1992, 96,

(G236) Wllde, C. P.; Hu, A.; Rondeau, C. M.; Wood, M. J. Electroanal. Chem.

(G239) Korell, U.; Spichiger, U. E. Electroanalysis 1993, 5, 869-876. (G240) Sim, K. W. Anal. Chim. Acta 1993, 273, 165-174. (G241) Fraser, D. M.; Zakeeruddin, S. M.; Gratzel, M. J. Electroanal. Chem.

(G242) Furbee, J. W.; Thomas, C. R.; Kelly, R. S.; Malachowski, M. R. Anal.

(G243) Atanasov, P.; Kalsheva, A.; Gamburzev, S.; Iliev, I.; Bobrin, S.

(G244) Zhao, S. S.; Luong, J. H. T. Anal. Chim. Acta 1993, 282, 319-327. (G245) Kulys, J.; Buchrasmussen, T.; Bechgaard, K.; Marclnkeviciene, J.;

1993, 26, 1281-1299.

287, 327-333.

59-70.

1993, 273, 187-193.

63, 2961-2965.

5641-5652.

1993, 353, 19-31.

1993, 359, 125-139.

Chem. 1993, 65, 1654-1657.

Electroanalysis 1993. 5, 91-97.

Hansen. H. E. Anal. Lett. 1993, 26, 2535-2542. (G246) Ikeda, T.; Kurosaki, T.; Takayama, K.; Kinoshita, H. Denki Kagaku

(G247) Takayama, K.; Kurosaki, T.; Ikeda. T. J. Electranal. Chem. 1993, 356, 1993, 67, 889-890.

295-301 - - - - - . . (G248) Cohen, C. B.; Weber, S. G. Anal. Chem. 1993, 65, 169-175. (G249) Ballarin, B.; Brumlik, C. J.; Lawson, D. R.; Liang, W. B.; Vandyke, L.

S.; Martin, C. R. Anal. Chem. 1992, 64, 2647-2651. (G250) Nikolelis, D. P.; Tzanelis, M. G.; Kruil, U. J. Anal. Chim. Acta 1993, 287,

569-576. (G251) Audebert, P.; Demallle, C.; Sanchez, C. Chem. Mater. 1993, 5, 911-

913. (G252) Ellerby, L. M.; Nishlda, C. R.; Nishida, F.; Yamanaka, S. A.; Dunn, B.;

Valentine, J. S.; Zink, J. 1. Science 1992, 255, 1113-1115. (G253) Palecek, E.; Jelen, F.; Teijeiro, C.; Fucik. V.; Jovin, T. M. Anal. Chim.

Acta 1993, 273, 175-186. (G254) Teijeiro, C.; Nejedly, K.; Palecek, E. J. Blomol. Struct. Dynam. 1993,

7 7 , 313-331. (G255) Maeda, M.; Mitsuhashi, Y.; Nakano, K.; Takagl, M. Anal. Scl. 1992, 8,

83-84. _ _ (G256) Millan. K. M.; Spurmanis, A. J.; Mlkkeisen, S. R. Electroanalys/s 1992,

4. 929-932. (0257) Rodriguez, M.; Bard, A. J. Inwg. Chem. 1992, 37, 1129-1135. (G258) Grover, N.; Gupta, N.; Singh, P.; Thorp, H. H. Inorg. Chem. 1992, 37,

(G259) Gupta, N.; Grover, N.; Neyhart, G. A.; Llang. W.; Slngh, P.; Thorp, H.

(G260) Ohasemzadeh, M. B.; Capella, P.; Mhcheil, K.; Adams, R. N. J. Neurochem.

20 14-2020.

H. Angew. Chem., Int. Ed. Engl. 1992, 37, 1046-1050.

1993, 60, 442-448.

(G261) Capella, P.; Ohasemzadeh, M. B.; Adams, R. N.; Wiedemann, D. J.; Wightman, R. M. J. N e m h e m . 1993, 60, 449-453.

(G262) Young, S. D.; Michael, A. C. Brain Res. 1993, 600, 305-307. (G263) Oneill, R. D. Analyst 1993, 778, 433-438. (G264) Wledemann, D. J.; Kawagoe, K. T.; Kennedy, R. T.; Ciolkowskl, E. L.;

Wightman, R. M. Anal. Chem. 1991, 63, 2965-2970. (G265) A m , W. J.; Boutelk M.G.; Gaky, P. T. J. Chem. Soc., Chem. Commun.

(G266) Hu, Y. 8.; Zhang, Y. N.; Wilson, G. S. Anal. Chlm. Acta 1993, 287,

(G267) Zhang, Y.; Wilson, G. S. Anal. Chlm. Acta 1993, 287, 513-520. (G268) Lau, Y. Y.; Abe, T.; Ewing, A. G. Anal. Chem. 1992, 64, 1702-1705. (G269) Lau, Y. Y.; Wong, D. K. Y . ; Ewlng, A. G. Mlcrochem. J. 1993, 47,

(G270) Chen, T. K.; Lau, Y. Y.; Wong, D. K. Y . ; Ewing, A. G. Anal. Chem. 1992,

(G271) Schroeder, T. J.; Jankowski, J. A.; Kawagoe, K. T.; Wightman, R. M.; Lefrou, C.; Amatore, C. Anal. Chem. 1992, 64, 3077-3063.

(G272) Kennedy, R. T.; Huang, L.; Atkinson, M. A.; Dush, P. Anal. Chem. 1993,

(G273) Limoges, B.; Degrand. C.; Brossier, P.; Blankespoor, R. L. Anal. Chem.

(G274) Lasalle, A. L.; Limoges. 8.; Anizon, J. Y.; Degrand, C.; Brossier, P. J. Electroanal. Chem. 1993, 350, 329-335.

(G275) Yamaguchi, S.; Ozawa, S.; Ikeda, T.; Senda, M. Anal. Scl. 1992, 8, 87-88.

(G276) Thompson, R. Q.; Porter, M.; Stuver, C.; Halsail, H. B.; Heineman, W. R.; Buckiey, E.; Smyth, M. R. Anal. Chim. Acta 1993, 277, 223-229.

(0277) Huet. D.; Bourdiilon, C. Anal. Chim. Acta 1993, 272, 205-212. (G278) Minami, H.; Sugawara. M.; Odashima, K.; Umezawa, Y.; Uto, M.;

Michaelis, E. K.; Kuwana, T. Anal. Chem. 1991, 63, 2787-2795. (G279) Odashima, K.; Kotato, M.; Sugawara, M.; Umezawa, Y. Anal. Chem.

1993, 65, 927-936. (G280) Nikoielis, D. P.; Tzanelis, M. G.; Krull, U. J. Anal. Chlm. Acta 1993, 282,

(G281) Wang, J.; Lin, Y. H.; Eremenko, A. V.; Kurochkin, I. N.; Mlneyeva, M.

(G282) Pierce, D. T.; Unwin, P. R.; Bard, A. J. Anal. Chem. 1992, 64, 1795-

(G283) Nhrens, D. E.; Chambers, J. Q.; Anderson, T. R.; White, D. C. Anal.

(G284) Plant, A. L. Langmuir 1993, 9, 2764-2767.

H. CHARACTERIZATION OF REDOX REACTIONS

(Hl)

(H2) (H3) (H4)

1992, 900-901.

503-5 1 1.

308-316.

64, 1264-1268.

65, 1882-1887.

1993, 65, 1054-1060.

527-534.

F. Anal. Chem. 1993, 65, 513-516.

1804.

Chem. 1993, 65, 65-69.

Bond, A. M.; Coiton, R.; Hutton, R. S. Inorg. Chim. Acta 1992, 200,

Plerce, D. T.; Gelger, W. E. J. Am. Chem. Soc. 1992, 7 74,6063-6073. Huang, Q. D.; Gosser, D. K. Tabnta 1992, 39, 1155-1161. Andrieux, C. P.; Delgado, G.; Saveant, J. M. J. Electroanal. Chem. 1993, 348. 123-139.

671-677.

Andiieux, C. P.; Differdlng, E.; Robert, M.; Saveant, J. M. J. Am. Chem. Soc. 1993. 775. 6592-6599. Yang, H. J'.; Bard, A. J. J. Electroanal. Chem. 1992, 339, 423-449. Yang, H. J; Wlpf, D. 0.; Bard, A. J. J. Electroanal. Chem. 1992, 337, 913-924. Andrieux, C. P.; Haplot, P.; Pinson, J.; Saveant, J. M. J. Am. Chem. Soc.

Bond, A. M.; Feldberg, S. W.; Greenhill, H. B.; Mahon, P. J.; Coiton, R.; Whyte, T. Anal. Chem. 1992, 64, 1014-1021. Lemos, M. A. N. D. A.; Pombeiro, A. J. L. J. Organomet. Chem. 1992,

Anxolabehere, E.; Lexa, D.; Saveant, J. M. J. phys. Chem. 1992, 96,

1993, 7 75, 7783-7788.

438, 159-165.

1266- 1270. -.. - . Brielbeck, B.; Ruhi, J. C.; Evans, D. H. J. Am. Chem. Soc. 1993, 775, 1 1898- 1 1905.

(H5)

(He) (H7)

(HE)

(H9)

WO)

(H1V

(H 12)

(H13) Nelsen, S. F.; Chen, L. J.; Petlllo. P. A.; Evans, D. H.; Neugebauer, F. A. J. Am. Chem. Soc. 1993, 775, 10611-10620.

(H14) Marioli, J. M.; Kuwana, T. Electrochim. Acta 1992, 37, 1167-1197. (H15) Burke, L. D.; Ryan, T. G. Electrochlm. Acta 1992, 37, 1363-1370. (H16) Becerik, I.; Kadirgan, F. Electrochim. Acta 1992, 37, 2651-2657. (H17) Parpot, P.; Kokoh, K. B.; Beden, B.; Lamy, C. Electrochim. Acta 1993,

(H18) Kokoh, K. B.; Leger, J. M.; Beden, B.; Lamy, C. Electrochlm. Acta 1992, 37, 1333-1342.

(H19) Kokoh, K. 8.; Parpot, P.; Belgsir, E. M.; Leger, J. M.; Beden, B.; Lamy. C. Electrochlm. Acta 1993, 38, 1359-1365.

(H20) Ruhl, J. C.; Evans, D. H.; Neta, P. J. Electroanal. Chem. 1992, 340,

(H21) Lavlron, E.; Meunier-Prest, R.; Vallat, A.; Roulliir, L.; Lacasse, R. J. Electroanal. Chem. 1992, 347, 227-255.

(H22) Danclu, V.; Martre, A. M.; Pouillen, P.; Mousset, G. Electrochim. Acta

38, 1679-1683.

257-272.

1992. 37. 1993-2000. (H23) Danciu, V.; Martre, A. M.; Pouillen, P.; Mousset, G. Electrochim. Acta

1992, 37, 2001-2008. (H24) Baumane, L.; Stradins, J.; Gavars, R.; Duburs, G. Electrochim. Acta

(H25) Dumanovlc, D.; Jovanovlc, J.; Suznjevlc, D.; Erceg, M.; Zuman, P. Electroanalysls 1992, 4, 795-800.

(H26) Miraliesroch, F.; Tallec, A.; Tardhrel, R. Electrochim. Acta 1993, 38,

(H27) Anne, A.; Hapiot, P.; Moiroux, J.; Neta, P.; Saveant, J. M. J. Am. Chem. SOC. 1992, 774, 4694-4701.

(H28) Anne, A.; Haplot, P.; Molroux, J.; Saveant, J. M. J. Electroanal. Chem. 1992, 337, 959-970.

1992, 37, 2599-2610.

963-968.


Medebieiie, M.; Pinson, J.; Saveant, J. M. Tetrahedron Le#. 1002, 33,

Combellas, C.; Marzouk, H.; Suba, C.; Thiebault, A. Synthesis 1003,

Mortensen, J.; Heinze, J.; Herbst, H.; Muiien, K. J. Elecfroanal. Chem.

7351-7354.

788-790.

1092, 324, 201-217. Cieghorn, S. J. C.; Pietcher, D. Elecfrochim. Acta 1093. 38, 425-430. Cleghorn, S. J. C.; Pletcher, D. Electrochim. Acfa 1003, 38, 2683- 2689. khdavi , B.; Chapuzet, J. M.; Lessard, J. Electrochim. Acta 1003, 38,

Momota, K.; Morlta, M.; Matsuda, Y. Electrochim. Acta 1003, 38,619- 624. Deigado, M.; Wolf, R. E.; Hartman, J. R.; McCafferty, 0.; Yagbasan, R.; Rawie, S. C.; Watkin, D. J.; Cooper, S. R. J. Am. Chem. SOC. 1002,

Urove. G. A.; Peters, D. G. J. Electrochem. SOC. 1003, 740, 932-935. Pritts, W. A.; Vielra, K. L.; Peters, D. G. Anal. Chem. 1003, 65, 2145- 2149. Wandlowski, T.; Gosser, D.; Akinele, E.; DeLevie, R.; Horak, V. Taknta

Geiger, W. E.; Rieger, P. H.; Corbato, C.: Edwin, J.; Fonseca, E.; Lane, G. A.; Mevs, J. M. J. Am. Chem. Soc. 1003, 775, 2314-2323. Oseila, D.; Fiedier, J. Organometallics 1002. 77. 3875-3878. Oseila, D.; Posplsil, L.; Fiedier, J. Organometallics 1003, 72, 3140- 3144. Karpinski, 2. J.; Kochi, J. K. Inorg. Chem. 1002, 37, 2762-2767. Sanauiiah; Kano, K.; Glass, R. S.; Wilson, G. S. J. Am. Chem. SOC.

Savaranamuthu, A.; Bruce, A. E.; Bruce, M. R. M.; Fermin, M. C.; Hneihen, A. S.; Bruno, J. W. Organomfallics 1092, Boudon, C.; Gisselbrecht, J. P.; Gross, M.; Benabdailah, T.; Gugiieimetti, R. J. Elechoanal. Chem. 1003, 345, 363-376. McDevltt, M. R.; Addison, A. W. Inorg. Chim. Acta 1003,204,141-146. Desantis, G.; Fabbrizzi, L.; Licchelli, M.; Mangano, C.; Pallavicini, P.; Poggl, A. Inorg. Chem. 1003, 32, 854-860. Mu, X. H.; Schultr, F. A. Inorg. Chem. 1002, 37. 3351-3357. Chiistunoff, J. B.; Bard, A. J. Inorg. Chem. 1992, 37, 4582-4587. Chiistunoff, J. B.; Bard, A. J. Inorg. Chem. 1093, 32, 3521-3527. Bard, A. J.; Garcia, E.; Kukharenko, S.; Strelets, V. V. Inorg. Chem. 1903, 32, 3528-3531. Adeyemi, S. A.; Dovietogiou, A.; Guadaiupe, A. R.; Meyer, T. J. Inorg. Chem. 1002, 37, 1375-1383. Roffia, S.; Marcaccio, M.; Paradisi. C.; Paolucci, F.; Balzani, V.; Denti, G.; Serroni, S.; Campagna, S. Inorg. Chem. 1903, 32, 3003-3009. Krejcik, M.; Vicek, A. A. Inorg. Chem. 1092, 37, 2390-2395. Deblas, A.; Desantis, G.; Fabbrlzzi, L.; Liccheili, M.; Lanfredi, A. M. M.; Paiiavicinl, P.; Poggi, A.; Ugozzoii, F. Inorg. Chem. 1903, 32, 106-1 13. Kadish, K. M.; van Caemeibecke, E.; Boulas, P.; Dsouza, F.; Vogei, E.; Kisters, M.; Medforth, C. J.; Smith, K. M. Inorg. Chem. 1003, 32,4177- 4178. GuMi. D. M.; Hambright, P.; Lexa, D.; Neta, P.; Saveant, J. M. J. Phys. Chem. 1902, 96, 4459-4466. Kadish, K. M.; Hu, Y.; Boschl, T.; Tagliatesta, P. Inorg. Chem. 1093,

Kadish. K. M.; Dsouza, F.; van Caemelbecke, E.; Viilard, A.; Lee, J. D.; Tabard, A.; Guilard, R. Inorg. Chem. 1093, 32, 4179-4185. StoJanovic, R. S.; Bond, A. M. Anal. Chem. 1993, 65, 56-64. Kamlnsky, A.; Wiliner, I.; Mandier, D. J. Nectrochem. Soc. 1003, 740,

1377-1380.

774, 8983-8991.

1003, 40, 1789-1798.

1903, 775, 592-600.

32, 2996-3002.

L25-L27. Xie, Q. S.; Perezcordero, E.; Echegoyen, L. J. Am. Chem. SOC. 1902,

Zhou, F. M.; Jehouiet, C.; Bard, A. J. J. Am. Chem. SOC. 1002, 774, 7 74, 3978-3980.

11004-11006. Fawcett, W. R.; Opaiio, M.; Fedurco, M.; Lee, J. W. J. Am. Chem. SOC.

Krishnan, V.; Moninot, G.; Dubois, D.; Kutner, W.; Kadish, K. M. J. Electroanal. Chem. 1903, 356, 93-107. Mkkln, M. V.; Bulhoes, L. 0. S.; Bard, A. J. J. Am. Chem. Soc. 1003, 775, 201-204. Xie, Q. S.; Arias, F.; Echegoyen, L. J. Am. Chem. SOC. 1003, 175, 98 18-981 9. Guarr, T. F.; Meier, M. S.; Vance, V. K.; Clayton, M. J. Am. Chem. SOC. 1003, 7 75, 9862-9863. Penicaud, A.; Perezbenitez, A.; Gieason, R.; Munoz, E.; Escudero, R. J. Am. Chem. SOC. 1093, 775, 10392-10393. Li, Q.; Wudl, F.; Thiigen, C.; Whetten, R. L.; Diederich, F. J. Am. Chem.

Lerke, S. A.; Parkinson, E. A.; Evans, D. H.; Fagan, P. J. J. Am. Chem.

Koefod, R. S.; Xu, C. J.; Lu, W. Y.; Shapiey, J. R.; Hili. M. G.; Mann, K. R. J. Phys. Chem. 1002, 96, 2928-2930. Sudha, C.; Mandai, S. K.; Chakravarty, A. R. Inorg. Chem. 1903, 32,

Shibahara, T.; Yamasaki, M.; Sakane, 0.; Mlnami, K.; Yabuki, T.; Ichimura, A. Inorg. Chem. 1002, 37, 640-647. Coe, B. J.; Jones, C. J.; McCleverty, J. A,; Bruce, D. W. Inorg. Chlm. Acta 1903, 206, 41-46. Holder, G. N.; Bottomiey, L. A. Inorg. Chim. Acta 1002, 794, 133-137. Heath, G. A.; Raptis, R. G. J. Am. Chem, SOC. 1903, 175, 3768-3769. Oseiia, D.; Hanziik, J. Inorg. Chim. Acta 1003, 213, 31 1-317. Cyr, J. E.; Linder, K. E.; Nowotnik, D. P. Inorg. Chim. Acfa 1093, 206, 97-104. Choi, Y. K.; Kim, E. S.; Park, S. M. J. Electrochem. Soc. 1003, 140, 11-18. Opekar, F.; Langmaier, J. Talanta 1092, 39, 367-369.

1003, 175, 196-200.

SOC. lS02, 774, 3994-3996.

SOC. 1002, 114, 7807-7813.

380 1-3802.

(H83) Komeda. N.; Nagao, H.; Matsui, T.; Adachi. 0.; Tanaka, K.J. Am. Chem. SOC. 1992, 774, 3625-3630.

(H84) Ratliff, K. S.; Lentz, R. E.; Kublak, C. P. Organomefallics 1002, 77,

(Has) Arana, C.; Yan, S.; Keshavarzk, M.; POtts, K. T.; Abruna, H. D. Inwg. Chem. 1002, 37, 3680-3682.

(H86) Bruce. M. R. M.; Megehee, E.; Sullivan, B. P.; Thorp, H. H.; O’Tooie. T. 4864-4873. R.; Downard. A.; Pugh, J. R.; Meyer, T. J. Inorg. Chem. 1002, 37,

1986-1 988.

YoshMa, T.; Tsutsumtda. K.; Teratani, S.; Yasufuku, K.; Kaneko, M. J. Chem. Soc., Chem. Commun. 1003, 631-633. Bandi, A.; Kuhne, H. M. J. Elecfrochem. SOC. 1002, 739, 1605-1610. Kyrlacou, G.; Anagnostopoulos, A. J. Elecboanal. Chem. 1002. 328,

Schwartz, M.; Cook, R. L.; Kehoe, V. M.; Macduff, R. C.; Patei, J.; Sammells, A. F. J. Electrochem. Soc. 1093, 740, 614-618. Ohkawa, K.; Hashlmoto, K.; Fujishima, A.; Noguchi, Y.; Nakayama, S. J. Elecfroanal. Chem. 1003, 345, 445-456. Ohkawa, K.; Noguchi. Y.; Nakayama, S.; Hashimoto, K.; Fujishima. A. J. Elecfroanal. Chem. 1003, 346, 459-464. Kudo, A.; Nakagawa, S.; Tsuneto, A.; Sakata, T. J. Electrochem. SOC.

Nagaoka, T.; Nishii, N.; Fujii, K.; Ogura, K. J. Electroanal. Chem. 1002,

Derien, S.; Ciinet, J. C.; Dunach, E.; Perichon, J. J. Organomefal. Chem.

Derien, S.; Clinet, J. C.; Dunach, E.; Perichon, J. J. Org. Chem. 1093,

233-243.

1903, 740, 1541-1545.

322, 383-389.

1002, 424. 213-224.

58, 2578-2588. (H97) Derien, S.; Ciinet, J. C.; Dunach, E.; Perichon, J. Tetrahedron 1902, 48,

(H98) Murcla, N. S.; Peters, D. G. J. Etectroanal. Chem. 1992, 326, 69-79. (H99) Ogura, K.; Mine, K.; Yano, J.; Sugihara, H. J. Chem. Soc., Chem.

Commun. 1093, 20-21. (H100) Kyrlacou, G. 2.; Anagnostopoulos, A. K. J. Appl. Electrochem. 1003,

(HlOl) Naitoh, A.; Ohta, K.; Mizuno, T.; Yoshde, H.; Sakai, M.; Node, H. Electrochim. Acfa 1003, 38, 2177-2179.

(H102) Yahikozawa, K.; Nishimura, K.; Kumazawa. M.; Tateishi, N.; Takasu, Y.; Yasuda. K.; Matsuda, Y. Electrochim. Acta 1002, 37, 453-455.

(H103) Aramata. A.; Toyoshima, I.; Enyo, M. Electrochim. Acta 1092, 37,

(H104) Bronoei, G.; Besse, S.; Tassin, N. Electrochlm. Acfa 1002, 37. 1351-

(H105) Lai, Y. K.; Wong, K. Y. Electrochim. Acta 1903. 38, 1015-1021. (H106) Wong, K. Y.; Yam, V. W.; Lee, W. W. Nectrochim. Acta 1002, 37.

(H107) Cavalca, C. A.; Larsen, G.; Vayenas, C. 0.; Hailer, G. L. J. phys. Chem.

(H108) Gasteiger, H. A.; Markovlc, N.; Ross, P. N.; Cairns, E. J. J. Phys. Chem.

(H109) Karaman, R.; Jeon, S. W.; Aimarsson, 0.; Bruice, T. C. J. Am. Chem.

(H110) Hofseth, C. S.; Chapman, T. W. J. Electrochem. SOC. 1002, 739,2525-

(H111) Farmer, J. C.; Wang, F. T.; Lewis, P. R.; Summers, L. J. J. Electrochem.

(H112) Lahiri, G. K.; Schussel, L. J.: Stoizenbera, A. M. Inora. Chem. 1002.

5235-5248.

23, 483-486.

131 7-1320.

1353.

2645-2650.

1003, 97, 6115-6119.

1093. 97. 12020-12029.

SOC. 1902, 7 74, 4899-4905.

2529.

SOC. 1002, 739, 3025-3029. -

37, 4991-5000. (Hl13) Lojou, E.; Devaud, M.; Heintz, M.; Troupel, M.; Perichon, J. Electrochim.

(H114) Che, G. L.; Dong, S. J. Electrochim. Acfa 1903. 36, 1345-1349. (H115) Ma, L.; Li, H. L.; Cai, C. L. Electrochim. Acfa 1003, 38, 2773-2775. (H116) Gur. T. M.; Huggins, R. A. J. Electrochem. Soc. 1002, 739, L95-L97. (H117) Matsumoto, Y.; Sasaki, T.; Hombo, J. Inorg. Chem. 1002, 37, 738-

(H118) Wade, T.; Park, J. M.; Garza, E. G.; Ross, C. B.; Smith, D. M.; Crooks,

(H119) Singh, K.; Tanveer, R. J. Meter. Sci. Left 1003, 72, 737-738. (H120) Slngh. K.; Tanveer. M. R. J. Meter, Chem 1003, 3, 1295-1298. (H121) Singh, K.; Shukla, A. K. Sol. Energ. Mater. Sol. Cells 1003, 30. 169-

Acta 1903, 38, 613-617.

741.

R. M. J. Am. Chem. Sm. 1002, 774, 9457-9464.

175 (H122) Dennison, S. Electrochim, Acfa 1003, 38, 2395-2403. (H123) Roberts, G. L.; Kauziarich, S. M.; Glass, R. S.; Estili, J. C. Chem. Mater.

1093. 5. 1645-1650. (H124) Chakravorti, M. C.; Subrahmanyam, G. V. B. Po/yhedron 1002, 77,

(H125) Warren, C. J.; Ho, D. M.; Bocarsly, A. B.; Haushalter, R. C. J. Am. Chem.

(H126) Niyazymbetov. M. E.; Evans, D. H. J. Org. Chem. 1093.58, 779-783. (H127) Niyazymbetov, M. E.; Evans, D. H. Tetrahedron 1093, 49,9627-9688. (H128) Jutand, A.; Negri, S.; Mosieh, A. J. Chem. Soc., Chem. Commun. 1092.

(H129) Heintz. M.; Devaud, M.; Hebri, H.; Dunach, E.; Troupei, M. Tefrahedron

(H130) Gard. J. C.; Lessard, J.; Mugnier, Y. Nectrochim. Acta 1993, 38, 677-

(H131) Momota, K.; Morita. M.; Matsuda, Y. Electrochim. Acta 1093,36,1123-

(H132) Wendt, H.; Bitterllch, S. Electrochim. Acta 1092. 37, 1951-1958. (H133) Wendt, H.; Bitterlich, S.; Lodowicks, E.; Liu, 2. Electrochlm. Acfa 1092,

(H134) Hughes, D. L.; Ibrahim, S. K.; Macdonald, C. J.; Ail, H. M.; Pickett, C.

(H135) Markovic, N.; Ross, P. N. J. Phys. Chem. 1093, 97, 9771-9778. (H136) Casanova, E. A.; Dutton. M. C.; Kalota, D. J.; Wagenknecht, J. H. J.

3 19 1-31 95.

Soc. 1993, 175. 6416-6417.

1729-1730.

1003, 49, 2249-2252.

680.

1130.

37, 1959-1969.

J. J. Chem. Soc., Chem. Common. 1902, 1762-1763.

Electrochem. Soc. 1003, 740, 2565-2567.

Analytical Chemistw, Vol. 66, No. 12, June 15, 1994 425R

(H137) Franklin, T. C.; Oliver, G.; Nnodimele, R.; Couch, K. J. Electrochem. SOC. 1992, 739, 2192-2195.

(H138) Kunai, A.; Toyoda, E.; Kawakami, T.; Ishikawa, M. Organometallics 1992, 7 7, 2899-2903.

(H139) Chakravwti, M. C.; Ganguly, S.; Subrahmanyam, G. V. B.; Bhattacharb. M. Po/yhedron 1993, 72, 683-687.

(HMO) Caron, C.; Subramanian, R.; Dsouza, F.; Kim, J.; Kutner, W.; Jones, M. T.: Kadish, K. M. J. Am. Chem. SOC. 1993, 775, 8505-8506.

(H141) Bouzek, K.; Rousar, I. Electrochim. Acta 1993, 38, 1717-1720. (H142) Nikitas, P. J. Electroanal. Chem. 1993, 348, 59-80. (H143) Myers, S. A.; Mackay, R. A.; Brajter-Toth, A. Anal. Chem. 1993, 65,

(H144) Abbott, A. P.; Gounili, G.; Bobbin, J. M.; Rusling, J. F.; Kumosinski, T.

(H145) Abbott, A. P.; Miaw, C. L.; Rusling, J. F. J. Nectroanai. Chem. 1992,

(H146) Gounili, G.; Miaw, C. L.; Bobblt, J. M.; Rusling, J. F. J. ColioidInterface

(H147) Kamau, G. N.; Hu, N. F.; Rusling, J. F. Langmuir 1992, 8, 1042-1044. (H148) Iwunze, M. 0.; Hu. N. F.; Rusling, J. F. J. Electroanal. Chem. 1992, 333,

(H149) Sucheta, A.; Haque, I. U.; Rusling, J. F. Langmuir 1992, 8, 1633-1636. (H150) Takisawa, N.; Thomason, M.; Bloor, D. M.; Wynjones, E. J. Colloid

(H151) Phani, K.L.N.; Pitchumani,S.;Ravichandran,S.;Sekan, S.T.;Bharathey,

3447-3453.

F. J. Phys. Chem. 1992, 96, 11091-11095.

327, 31-46.

Sci. 1992, 753, 446-456.

353-36 1.

Interface Sci. 1993, 757, 77-81.

S. J. Chem. Soc., Chem. Commun. 1993, 179-181.

I. SPECTROELECTROCHEMISTRY

Pastor, E.; Schmidt, V. M.; Iwasita, T.; Arevalo, M. C.; Gonzaiez, S.; Arvia, A. J. Nectrochim. Acta 1993, 38, 1337-1344. Pastor, E.: Wasmus, S.; IwasZa,T.; Arevalo, M. C.; Gonzalez, S.; ANia, A. J. J. Electroanal. Chem. 1993, 353, 81-100. Pastor, E.; Wasmus, S.; Iwaslta, T.; Arevalo, M. C.; Gonzalez, S.; Arvia, A. J. J. Nectroanal. Chem. 1993, 350, 97-116. Wasmus, S.; Vielstlch, W. J. Appi. Electrochem. 1993, 23, 120-124. Munk, J.; Skou, E. SolM State Ionics 1992, 53-56, 875-881. Schmlemann, U.; Baltruschat, H. J. Electroanai. Chem. 1993, 347, 93-109. Wasmus, S.; Vielstich, W. J. Electroanal. Chem. 1993, 359, 175-191. Anastasijevic, N. A.; Baltruschat, H.; Heitbaum, J. Electrochim. Acta

Wasmus, S.; Vielstich, W. Nectrochim. Acta 1993, 38, 185-189. Jusys, 2.; Vaskelis, A. J. Electroanal. Chem. 1992, 335, 93-104. Wasmus, S.; Vielstich, W. J. Nectroanal. Chem. 1993, 345, 323-335. Wasmus, S.; Vielstich, W. Nectrochim. Acta 1993, 38, 175-183. Cattaneo, E.; Rasch, B.; Vielstich, W. J. Appl. Nectrochem. 1991, 27, 885-894. Wasmus, S.; Vielstich, W. Nectrochim. Acta 1993, 38, 541-552. Bittins-Cattaneo, B.; Wasmus, S.; Lopez-Mlshima, B.; Vielstich, W. J. Appl. Electrochem. 1993, 23, 625-630. Baltruschat, H.; Beltowska-Brzezinska, M.; Dulberg, A. Nectrochim. Acta 1993, 38, 281-284. Wasmus, S.; Vielstich, W. Electrochim. Acta 1993, 38, 185-189. Jusys, Z.: Liaukonis, J.; Vaskelis, A. J. Nectroanai. Chem. 1992, 325, 247-255. Schmidt, V. M.; Vielstich, W. Ber. Bunsenges. Phys. Chem. 1992, 96, 534-537. Hambitzer, G.; Joos. M.; Schriever, U. DECHEMA Monogr. 1992, 725, 501-509. Fujihira, M.; Noguchi, T. J. Electroanai. Chem. 1993, 347, 457-463. Herron, M. E.; Doyle, S. E.; Roberts, K. J.; Robinson, J.; Walsh. F. C. Rev. Sci. Instrum. 1992, 63, 950-955. Robinson, K. M.; O'Grady, W. E. Rev. Sci. Instrum. 1993, 64, 1061- 1065. Chabala, E. D.; Harii, B. H.; Rayment. T.; Archer, M. D. Langmuir1992,

1993, 38, 1067-1072.

8, 2028-2033. Yee, H. S.; Abruiia, H. D. Langmuir 1993, 9, 2460-2469. Durand, R.; Faure, R.; Aberdam, D.; Salem, C.; Tourillon, G.; Guay, D.; Ladouceur, M. Nectrochim. Acta 1992, 37, 1977-1982. McBreen, J. J. Nectroanal. Chem. 1993, 357, 373-386. Evans. R. W.: Godfrev. D.: Cowle. B.: Attard. G. A. J. Nectroanal. Chem. l992,'340, 385-37i. Guav, D.: Tourillon, G.; Laoerriere, G.; Belanper. D. J. Phys. Chem. 1992- 96, 7718-7724. '

Reimers, J. N.; Dahn, J. R. J. Electrochem. SOC. 1992, 739, 2091- .

Gustafsson. T.; Thomas, J. 0.; Koksbang, R.; Farrington, G. C. Electrochim. Acta 1992. 37, 1639-1643. Herron, M. E.; Pletcher. D.; Walsh, F. C. J. Electroanal. Chem. 1992, 332, 183-197. Druska, P.; Strehblow, H.-H. J. Electroanai. Chem. 1992, 335, 55-65. Bardwell, J. A.; Sproule, G. I.; MacDougall, B.; Graham, M. J.; Davenport, A. J.; Isaacs, H. S. J. Nectrochem. SOC. 1992, 739, 371-373. Skotheim, T. A.; Yang, X. Q.; Xue, K. H.; Lee, H. S.; McBreen, J.; Lu, F. Electrochim. Acta 1992, 37, 1635-1637. Bommarito. G. M.; Acevedo, D.; AbruRa, H. D. J. Phys. Chem. 1992,

Robinson, K. M.; Robinson, I. K.; O'Grady, W. E. Electrochim. Acta

Herron, M. E.; Doyle, S. E.; Pizzini, S.; Roberts, K. J.; Robinson, J.; Hards, G.; Walsh, F. C. J. Electroanai. Chem. 1992, 324, 243-258. Wei, W.; Xie, Q.; Yao, S. J. Electroanai. Chem. 1992, 328, 9-20. Xie, Q.; Wei, W.; Nie, L.; Yao, S. J. Nectroanai. Chem. 1993, 348, 29-47. Wei, W.; Xie, 0.; Yao, S. J. Electroanai. Chem. 1992, 334, 1-1 1.

96, 3416-3419.

1992, 37, 2169-2172.

Xie, Q.; Wei, W.; Nie, L.; Yao, S. Anal. Chem. 1993, 65, 1688-1892. Xie, Q.; Shen, D.; Nie, L.; Yao, S. Electrochim. Acta 1993, 38, 2277- 2280. Dong, S.; Xie, Y. J. Nectroanal. Chem. 1992, 335, 197-205. Xie, Q.; Wei, W.; Chen, X.; Nie, L.; Yao, S. J. Electrosnal. Chem. 1993, 357, 91-103. Zamponi, S.; Czerwinski, A.; Gambini. G.; Marassl, R. J. Electroanal. Chem. 1992, 332, 63-71. Piraud,, C.; Mwarania, E.; Wylangowski, G.; Wilkinson, J.; O'Dwyer, K.; Schiffrin, D. J. Anal. Chem. 1992, 64, 651-655. Kim, S.; Scherson, D. A. Anal. Chem. 1992, 64, 3091-3095. Olivi, P.; Pereira, E. C.; Longo, E.; Varella, J. A,; BulhBres, L. 0. des. J. Electrochem. SOC. 1993, 740, L81-L82. Anjo, D. M.; Brown, S.; Wang, L. Anal. Chem. 1993, 65, 317-319. Salbeck, J. J. Electroanal. Chem. 1992, 340, 169-195. Salbeck, J. Anal. Chem. 1993, 65, 2169-2173. Shimazu, K.; Yanagida, M.; Uosaki, K. J. Nectroanal. Chem. 1993,350,

Compton, R. G.; Fisher, A. C.; Wellington, R. G.; Winkler, J. J. Phys. Chem. 1992, 96, 8153-8157. Compton, R. G.; Fisher, A. C.; Wellington, R. G.; Winkler, J.; Bethell, D.; Lederer, P. J. Chem. Soc., Perkin Trans. 2 1992, 1359-1362. Littig, J. S.; Nieman, T. A. Anal. Chem. 1992, 64, 1140-1 144. Taniguchi, I.; Fujlwara, T.; Tomlnaga, M. Chem. Lett. 1992, 1217- 1220. Lee, Y. F.: Kirchoff, J. R. Anal. Chem. 1993, 65, 3430-3434. WaRon, D. J.; Phull, S. S.; Bates, D. M.; Lorimer, J. P.; Mason, T. J. Electrochim. Acta 1993, 38, 307-310. Mamantov, G.; Sienerth, K. D.; Lee, C. W.; Coffield, J. E.; Willlams. S.

321-327.

D. J. Electrochem. Soc. 1992, 739, L58-L59. Wang, 2.; Jin, X.; Cai, S.; Liu, Y.; Fujishima, A. Electrochim. Acta 1993,

Roth, J. D.; Weaver, M. J. Langmuir 1992, 8, 1451-1458. Zippel, E.; Kellner, R.; Krebs, M.; Brelter, M. W. J. Electroanal. Chem.

Zhao, M.; Wang, K.; Scherson, D. A. J. Phys. Chem. 1993, 97,4488- 4490. Anderson, M. R.; Huang, J. J. Electroanal. Chem. 1991, 378,335-347. Lin, W.-F.; Sun, S.-G.; Tian, La. ; Tian, L W . Electrochlm. Acta 1993,

(161)

(162) (163)

(164)

(165) (166)

38, 267-269.

1992, 330, 521-527.

38. 1107-1114. Ogasawara. H.; Sawatari. Y.; Inukai, J.; Ito, M. J. Electroanal. Chem.

Faguy, P. W.; Fawcett, W. R.; Liu, G.; Motheo, A. J. J. Electroanal. Chem. 1992, 339, 339-353. Bewick, A.; Gutierrez, C.; Larramona, G. J. Electroanai. Chem. 1992,

Boonekamp. E. P.; Kelly, J. J.; van der Ven, J.; Sondag, A. H. M. J. Electroanal. Chem. 1993, 344, 187-198. Bewick, A.; Gutierrez, C.; Larramona, G. J. Electroanai. Chem. 1992, 332, 155-167. Zhang, J.; Anson, F. C. J. Electroanal. Chem. 1992, 337, 945-957. Saez, E. I.; Corn, R. M. Electrochim. Acte 1993, 38, 1619-1625. Kitamura, F.; Ohsaka, T.; Tokuda, K. J. Electroanal. Chem. 1993, 353,

Bauscher, M.; Mantele, W. J. Phys. Chem. 1992, 96, 11101-11108. Krejclk. M.: Danek. M.; Hartl, F. J. Electroanal. Chem. 1991, 377, 179- 187. Graham, P. J.; Curran, D. J. Anal. Chem. 1992, 64, 2688-2692. Johnson, B. W.; Doblhofer, K. Electrochim. Acta 1993, 38, 895-701. Johnson, B. W.; Bauhofer, J.; Doblhofer, K.; Pettinger, B. Electrochim. Acta 1992, 37, 2321-2329. Budevska, B. 0.; Grifflths, P. R. Anal. Chem. 1993, 65, 2963-2971. Beden, B. J. Nectroanal. Chem. 1993, 345, 1-12. Lopes, M. I.; Fonseca, I.; Olivi, P.; Beden, B.; Hahn, F.; Leger, J. M.; Lamy, C. J. Nectroanal. Chem. 1993, 346, 415-432. Russell, A. E.; Lin, A. S.; O'Grady, W. E. J. Chem. SOC., Faraday Trans. 1993, 89, 195-198. Russell, A. E.; Williams, G. P.; Lin, A. S.; O'Grady, W. E. J. Electroanal. Chem. 1993, 356, 309-315. Zhang, Y.; Gao, X.; Weaver, M. J. J. Phys. Chem. 1993, 97, 8656- 8683.

1993, 358, 337-342.

333, 165-175.

323-328.

(186) Zhang, Y.; Weaver, M. J. J. Nectroanal. Chem. 1993, 354, 173-188. (187) Kondarkles, D. I.; Papatheodorou, G. N.; Vayenas, C. G.; Veryklos, X.

E . Ber. Bunsenges. Phys. Chem. 1993, 97, 709-720. (188) Mayer, S. T.; Muller, R. H. J. Electrochem. SOC. 1992, 739, 426-433. (189) Arsov, L. D.; Kormann, C.; Plieth, W. J. Raman Spectrosc. 1991, 22,

573-575. (190) Pemberton, J. E.: Bryant, M. A.; Sobocinski, R. L.; Joa, S. L. J. Phys.

Chem. 1992, 96, 3776-3782. (191) Pemberton, J. E.; Sobocinski, R. L. J. Electroanal. Chem. 1991, 318,

(192) Joa, S. L.; Pemberton, J. E. J. Phys. Chem. 1993, 97, 9420-9424. (193) Joa, S. L.; Pemberton, J. E. Langmuir 1992, 8, 2301-2310. (194) Sobocinski, R. L.; Pemberton, J. E. Langmuir 1992, 8, 2049-2063. (195) Potahl, G.; Barthelmes. J.; Pleith, W. J. Electroanai. Chem. 1992, 329,

329-338. (196) Davis, K. L.; McGlashen, M. L.; Morrls, M. D. Langmuir 1992, 8, 1854-

1658. (197) Hoke, R. Electrochim. Acta 1993, 38, 947-956. (198) Bukowska, J.; Jakowska, K. J. Nectroanal. Chem. 1992, 322, 347-

356. (199) Ingram, J. C.; Pemberton, J. E. Langmuir 1992, 8, 2034-2039. (1100) Ingram, J. C.; Pemberton, J. E. Langmuir 1992, 8, 2040-2048. (1101) Bryant, M. A.; Joa, S. L.; Pemberton, J. E. Langmuir1992, 8, 753-756. (1102) Barthelmes. J.; Potahl, G.; Plieth, W. J. Electroanai. Chem. 1993, 349,

157-169.

223-231.


(1103) Saito, H. Bull. Chem. Soc. Jpn. 1993, 66, 963-965. (I 104) De Santana, H.; Temperini, M. L. A.; Rubim, J. C. J. Electroanal. Chem.

(1105) Jackowska, K.; Bukowska, J.; Kudelski, A. J. Nectroanal. Chem. 1993,

(1106) Kudelski, A.; Bukowska, J. J. Mol. Struct. 1992, 275, 145-150. (1107) HIII, W.; Wehling, B. J. fhys. Chem. 1993, 97, 9451-9455. (1108) Gao, X.; Zhang, Y.; Weaver, M. J. Langmulr 1992, 8, 668-672. (1109) Turcotte, S. 6.; Benner, R. E.; Riley, A. M.; Li, J.; Wadsworth, M. E.;

Bodily, D. M. J. Electroanal. Chem. 1993, 347, 195-205. (1110) Oyama, M.; Okada, M.; Okazaki, S. J. Elecfroanal. Chem. 1993, 346,

(1111) Lee, S. 6.; Kim, K.; Kim, M. S. J. fhys. Chem. 1992, 96, 9940-9943. (1112) Lacconi, 0.; Reents, 6.; Plieth, W. J. Electroanal. Chem. 1992, 325,

(1113) Son. Y.; de Tacconi. N. R.; Raleshwar, K. J. Electroanal. Chem. 1993.

1993, 356, 145-155.

350, 177-187.

261-290.

207-217.

345, 135-146. (1114) Melendres, C. A.; Pankuch, M. J. Electroanal. Chem. 1992, 333, 103-

113. (1115) Shi, C.; Zhang, W.; Lombardl, J. R.; Birke, R. L. J. fhys. Chem. 1992,

96, 10093-10096. (1116) Misono, Y.; Shibasakl, K.; Yamasawa, N.; Mineo, Y.; Itoh, K. J. fhys.

Chem. 1993, 97, 6054-6059. ( I1 17) Palys, B. J.; Puppeis. G. J.; van den Ham, D.; Feii, D. J. Electroanal.

Chem. 1992, 326, 105-112. (1118) Simonet, J.; El Badre, M. C.; Cariou, M. J. Electfoanal. Chem. 1992,

(1119) Ei Badre, M. C.; Cariou, M.; Simonet. J. J. Electroanal. Chem. 1992,

(1120) Gourier, D.; Tranchant, A.; Baffier, N.; Messina, R. Nectrochim. Acta

(1121) Dunsch. L.; Petr, A. Bef. Bunsenges. fhys. Chem. 1993,97,436-439. (1122) Slerak, P. J.; Wieckowski, A. J. Electroanal. Chem. 1992, 339, 401-

410. (1123) Sendlfer, M. E.; Zhao, M.; Kim, S.; Scherson, D. A. Anal. Chem. 1993,

65, 2093-2095. (1124) Hamnett. A. J. Chem. SOC., Faraday Trans. 1993, 789, 1593-1607. (1125) Chao, F.; Costa, M.; Tadjeddine. A. J. Electroanal. Chem. 1992, 329,

(1126) Hillier, A. C.; Ward, M. D. Anal. Chem. 1992, 64, 2539-2554. (1127) Bacskai, J.; LangG.; Inzelt, G. J. Electroanal. Chem. 1991,379,55-69. (1128) Beck, R.; Pittermann, U.; Weii, K. G. J. Nectrochem. SOC. 1992, 739,

(1129) Lee, W.-W.; White, H. S.; Ward, M. D. Anal. Chem. 1993, 65, 3232-

334, 169-182.

327, 185-200.

1992. 37, 2755-2764.

3 13-327.

453-46 1.

3237. (1130) olidl& A.; Hillman, A. R.; Bruckenstein, S. J. Electroanal. Chem. 1991,

378. 411-420. (1131) Heusler, K. E.; Pietrucha, J. J. Electroanal. Chem. 1992, 329,339-350. (1132) Dusemund, C.; Schwftzgebel, G. Ber. Bunsenges. fhys. Chem. 1991,

(1133) Lin, 2.; Ylp, C. M.; Joseph, I. S.; Ward, M. D. Anal. Chem. 1993. 65, 95, 1543-1546.

1546-1551.

J. INSTRUMENTATION

(Jl) Gabrieili, C.; Huet, F.; Keddam, M. J. Electrochem. SOC. 1991, 138, L82-L84.

Amatore. C.; Lefrou, C. J. €lectroanal. Chem. 1992, 324, 33-58. Yamagishi, H. J. Nectroanal. Chem. 1992, 326, 129-137. Fidler, J. C.; Penrose, W. R.; Bobis, J. P. I€€€ Trans. Instrum. MS.

Senaratne, C,; Hanck, K. W. Anal. Instrum. 1992, 20, 1-22. Popkkov, G. S.; Schlndler, R. N. Rev. Sci. Instrum. 1992, 63. 5366- 5372. Schefold, J. J. Elechoanal. Chem. 1992, 341. 11 1-136, 225-233. Clark, S. R.; Paul. D. W.; Sundgren, H. Microchem. J. 1992, 46, 225- 233.

1992, 41, 308-310.

Dygas, J. R.; Fafiiek, G.; Durakpasa, H.; Brelter, M. W. J. Appl. Electrochem. 1993. 23, 553-558. Cruaiies, M. T.; Drlckamer, H. G.; Faulkner, L. R. J. fhys. Chem. 1992, 96. 9888-9892. Sachinidis, J.; Shalders, R. D.; Tregloan, P. A. J. Electroanal. Chem.

Van Manen, P. A.; Weewer, R.; dew%, J. H. W. J. Electrochem. SOC. 1992, 739, 1130-1 134. Sorrels, J. W.; Dewald, H. D. Electroanalysis 1992, 4 487-493. Hua, C.; Sagar, K. A.; McLaughlin, K.; Jorge, M.; Meanay, M. P.; Smyth, M. R. Analyst 1991, 716, 1117-1120. Igawa, M.; Takabayaski, Y.; Koizumi, T. Bull. Chem. SOC. Jpn. 1992,

Hevrovska. R. J. fhvs. Chem. 1993. 9. 1962-1964.

1992, 327, 219-234.

65, 1561-1565.

Zeyer, C.; Gruniger, H. R.; Dossenbach, 0. J. Appl. Electrochem. 1992, 22. 304-305. Kahnsky, A.; Willner, I.; Mandler, D. J. Nectrochem. SOC. 1993. 740,

Dueber, R. E.; Dickens, P. 0. J. Nectrochem. SOC. 1991, 738, L79-L80. Jermann, R.; Tercier, M.-L.; Buffie, J. Anal. Chim. Acta 1992, 269,

Mldgley. D. Analyst 1993, 178, 41-45. Moussy, F.; Harrison, D. J.; O'Brien, D. W.; Rajotte, R. V. Anal. Chem.

Watson. S. W.: Madsen. B. W. Corroslon 1992. 48. 727-733.

L25-L27.

49-58.

1993, 65, 2072-2077.

Malem, F.; Mandler, D. J: Nectrochem. SOC. 1992, 139, L65. Gutz, I. G. R.; Angnes, L.; Pedrotti, J. J. Anal. Chem. 1993, 65, 500- 503. Pedrotti, J.; Angnes, L.; Gutz, I. G. R. Nectroanalysls (N. Y.) 1992, 4, 635-642. Aidstadt, J. H.; Dewald, H. D. Anal. Chem. 1992, 64, 3176-3179. Tierney, M. J.; Kim, H.-0. L. Anal. Chem. 1993, 65, 3435-3440. Masuda, 305-31 1. H.; Tanaka, H.; Baba, N. Bull. Chem. SOC. Jpn. 1993, 66,

Tang, T. K. L.; Chan, K.-Y. J. Electmanal. Chem. 1992, 334, 65-80. Powell, B. R. Catal. Len. 1992, 75, 189-197. Coeuret, F. J. Appl. Electrochem. 1993, 23, 853-855. Popkirov, G. S. J. .€lectroanal. Chem. 1993, 359, 97-103. Kounaves, S. P.; Lu, D. D. Comput. Chem. 1992, 76. 29-33. Liao, S.-L.; Olson, C. L. Rev. Sci. Instrum. 1993, 64, 1809-1814. Andrieux, C. P.; Delgado, G.; Saveant, J.-M.; Su, K. B. J. Elechoanal. Chem. 1993, 348, 107-121.


Documents

Dynamic Electrochemistry Methodology and Application обзор 1994