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A Review of the Use of Surfactants inFlow Injection AnalysisDaniel Y. Pharr aa Department of Chemistry, Virginia Military Institute, Lexington,Virginia, USA

To cite this article: Daniel Y. Pharr (2011): A Review of the Use of Surfactants in Flow InjectionAnalysis, Analytical Letters, 44:13, 2287-2311

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Flow Injection Analysis

A REVIEW OF THE USE OF SURFACTANTS IN FLOWINJECTION ANALYSIS

Daniel Y. PharrDepartment of Chemistry, Virginia Military Institute, Lexington,Virginia, USA

This review aims to present recent accomplishments in flow injection analysis by the use of

surfactants, micellar systems, and cloud point extractions. The analysis of metals, pharma-

ceuticals, environmental samples, and samples of biological interest, as well as, surfactants

themselves is covered. General considerations of micellar systems and cloud point extrac-

tions are briefly reviewed along with references to works that cover these fundamentals in

greater detail. Highlights of the current work in these areas are given to stress the advan-

tages of employing surfactants as an analytical tool to facilitate the experimental uses of

these reagents and their future possibilities in green chemistry and automated laboratory

techniques.

Keywords: Analysis; Cloud point extractions; CPE; FIA; Flow injection analysis; Micelles; Surfactants

INTRODUCTION

This review will focus on the uses of surfactants and micellar systems whenused in conjunction with flow injection analysis (FIA). The use of these reagentscontinues to spread into many fields of chemistry, especially with the growingemphasis on using greener chemical processes. The IUPAC names and CAS numbersfor most of the chemicals mentioned in this review are found between fbracketsg andare meant to aid the reader in being able to find these chemicals if difficulty ariseswith the common name. Some of the more commonly mentioned surfactants arefound in Table 1. Surfactants have several major properties that can be utilizedfor the desired results, such as solubilization, catalysis, and extraction. Severalreviews on the use of surfactants in analytical chemistry have been published pre-viously (Hinze 1979; Cline-Love, Habarta, and Dorsey 1984). The aggregation ofmolecules into micelles occurs at the cmc, critical micelle concentration. In water,the cmc has the hydrophilic head groups facing towards the aqueous solutionwith the hydrophobic long chain hydrocarbon facing towards a center of a three

Received 26 July 2010; accepted 21 October 2010.

Address correspondence to Daniel Y. Pharr, Department of Chemistry, VMI, Lexington, VA,

24450, USA. E-mail: pharrdy@vmi.edu

Analytical Letters, 44: 2287–2311, 2011

Copyright # Taylor & Francis Group, LLC

ISSN: 0003-2719 print=1532-236X online

DOI: 10.1080/00032719.2010.551689

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dimensional ellipsoid or sphere. This interior space is where the non-polar organiccompounds can be solubilized. Generally, the type of polar head group indicatesone of four surfactant types: cationic, anionic, zwitterionic and nonionic. A populartype of the non-ionic surfactant has polyoxyethylenated head groups, which formhydrated coils in the outer region of the micelle. The ability of organic reagents tobe dissolved in water that contains micelles can lead to the catalysis of the reactionbetween the reagents and the analyte. For example, when the cationic micelle attractsthe anionic analyte, it facilitates a faster kinetic reaction by its proximity to theorganic reagent inside the micelle than a reaction based on random collisions in asolution. The use of surfactants as extracting agents will also be considered in thisreview.

Another unique aspect of some surfactants is their ability to separate into twolayers, effectively creating a cloud point, by a change in the solution’s temperatureeither upon heating (non-ionic surfactants, lower layer) or cooling (zwitterionic sur-factants, upper layer). The surfactant layer takes any micelle solubilized species withit, resulting in a cloud point extraction. The species being separated in this mannerneeds to be sufficiently hydrophobic to be quickly and quantitatively trapped in themicelle. This process can act as a separation step and a preconcentration step. Theuse of cloud point extractions (CPE), in all aspects of analytical chemistry has beenthe subject of several noteworthy reviews (Bezerra, Arruda, and Ferreira 2005; Hinzeand Pramauro 1993; Hinze and Quina 1999; F. S. Silva et al. 2006).

The temperature at which a CPE occurs can be altered by the addition of saltsor other surfactants (Komaromy-Hiller, Calkins, and von Wandruszka 1996;Nascentes and Arruda 2003; F. S. Silva et al. 2006), which may also alter the cmc.For Triton X-100 with a cloud point of 73�C, cloud point temperature was raisedto 98�C when mixed with SDS. With the addition of only NaCl, the temperaturewas reduced to 56�C. However, a mixture of SDS and NaCl decreased the cloudpoint temperature to as low as 11.8�C (Nascentes and Arruda 2003). Buffers alsoaffect cloud point temperatures. Glycol additives and triblock polymers have been

Table 1. The more popular surfactants mentioned in this review

SDSx: sodium dodecyl sulfate, sodium lauryl sulfate, C12H25SO4Na, 288.38 g=mol, CAS No. 151-21-3

Anionic cmc¼ 7–10mM, Aggregation Number: 62

CTAC: cetyl trimethylammonium chloride, hexadecyltrimethylammonium chloride, C19H42NCl,

320.05 g=mol, CAS No. 112-02-7, Cationic cmc¼ 1.3mM, AggNo 90

CTABx: cetyl trimethylammonium bromide, hexadecyltrimethylammonium bromide, C19H42NBr,

364.5 g=mol, CAS No. 57-09-0, Cationic cmc¼ 1mM, AggNo 170

CPCy: cetyl pyridinium chloride, 1-hexadecylpyridinium chloride monohydrate, C21H38NCl.H2O,

358.01 g=mol, CAS No. 123-03-5, Cationic cmc¼ 0.90mM, 0.12mM, AggNo 95

Tween-80x: polyoxyethylene(20)sorbitan monooleate, C64H124O26, 1310 g=mol, density 1.064 g=mL,

CAS No. 9005-65-6, Non-ionic cmc¼ 0.012mM, AggNo¼ 58, Cloud point¼ 65�CTriton X-100x: t-octylphenoxypolyethoxyethanol, C34H62O11, 625 g=mol., density 1.07 g=mL, CAS

No.9002-93-1, Non-ionic cmc¼ 0.2–0.9mM, AggNo 140, Cloud point¼ 65�CTritonX-114x: polyethylene glycol tert-octylphenyl ether, (C2H4O)n C14H22O, n¼ 7=8, 537 g=mol,

d¼ 1.058 g=mL CAS No.9036-19-5, Non-ionic, cmc¼ 0.20-0.35mM), Cloud point¼ 23�C(xValues from Sigmaaldrich.com Detergent Selection Guide, yCline-Love et al. 1984)

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shown to cause significant depressions in the cloud points of Tween 20 and Tween 80(Mahajan, Chawla, and Bakshi 2004).

The classical CPE separation technique uses gravity or a centrifuge to affect theseparation, but flow injection analysis often uses a column. This method thus reducesthe volume of chemicals used, making it more efficient. Furthermore, surfactants areless toxic and flammable than organic solvents. The FIA technique has an in-linemini-column, and the thicker, less soluble portion of the solution, containing thecloud point surfactant and any species trapped in the collapsed micellar system, iscollected onto the column material. Several materials have been used for the column:alumina, silica, ODS (octadecylsilane bonded phase), nylon fiber, glass wool, cottonfiber, and others. The surfactant rich material can be washed off the column after theseparation of phases with a change in temperature or with an appropriate solvent.Tested solvents include acetonitrile, methanol, acids, another surfactant system, orwater. On-line preconcentration FIA reduces sample contamination and solvent con-sumption. Although CPE sample preconcentration has been widely reported formetal determination using flame atomic absorption spectroscopy (FAAS), electro-thermal atomic absorption spectroscopy (ETAAS), and inductively coupled plasma(ICP), there may be signal enhancement for anionic or depression for both non-ionicand cationic surfactants due to the surfactants themselves (Pharr et al. 1991). There-fore, standards should not be made in pure water. Smaller volumes of FIA-CPEsamples are an advantage to most ICP nebulization systems, but too much carboncan cause both physical and spectral interferences as with chromium determination(Bezerra et al. 2005).

Certain surfactants have advantages over others. In the list for Table 1, cetylpyridinium chloride (CPC), and Triton X-100 absorb in the UV region making themunsuitable for some types of analysis. Triton X-114 has been the surfactant of choicefor most of CPE studies because of its low cloud point temperature of 23�C. Whenother surfactants such as sodium dodecyl sulfate (SDS) or cetyl trimethylammoniumbromide (CTAB) are added to Triton X-114, the cloud point increases to about50�C. Furthermore, the addition of inorganic salts causes a small temperaturedecrease. However, when both surfactants and salts are present, there is a markeddecrease in the cloud point, especially with potassium sulfate and salt mixtures witheither SDS or CTAB (Gu and Galera-Gomez 1995). In a study of the effect oforganic solvents on Triton X-100, it was reported that polar organics, those com-pletely soluble in water, increased the cloud point while non-polar organics, partiallysoluble in water, decreased the cloud point (Gu and Galera-Gomez 1999). Mixturesof non-ionic surfactants were shown to have cloud points that vary between thecloud points of each individual surfactant, allowing the researcher to control theCPE temperature (Hinze and Pramauro 1993). Zwitterionic surfactants have notbeen used with FIA, but they are generally considered milder reagents and thus havebeen used in biochemical applications. Their cloud points occur as the temperature islowered. The addition of organic solvents, salts, and other micelles to zwitterionicsurfactants have been studied and have been shown to cause both cloud point eleva-tions and depressions, depending on the reagent. Urea and iodide lower the cloudpoint while sulfate increases it (Hinze and Pramauro 1993). Further work in this areashould be forthcoming.

A REVIEW OF SURFACTANTS IN FLOW INJECTION ANALYSIS 2289

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DETERMINATION OF METALS

Micelles alter the microenvironment and change the solution properties of water;this change has been the focus of numerous studies over the past decade (summarizedin Table 2). The blue complex of cobalt (II)’s reacts with thiocyanate; while colorless inwater, it is blue in organic liquids such as alcohol and acetone. The use of surfactantTween-80 to eliminate organic solvents was applied for the FIA determination ofcobalt (II) spectrophotometric detection at 625nm; a detection limit of 1.20mg=Lwithan upper limit of 750.0mg=L was achieved using a 5.0mL sample loop (Pharr andOstlund 2003). The catalytic abilities of surfactant TritonX-100 were highlighted inthe FIA analysis of cobalt (II) and nickel (II) using PAR, f4-(2-pyridylazo) rescorci-nol, CAS No. 13311-52-9g, in which the colored metal complex was formed withoutthe need of a 15min hot water bath. The SDS and CPC were also studied as surfac-tants for this procedure. Beer’s Law was obeyed at 510nm from 0.25 to 3.00mg=Lfor both metals (Pharr, Sienerth, and Tutor 2004). Several cationic surfactants includ-ing CPC, CTAB, and tetradecyltrimethylammonium bromide were used in the FIAspectrophoto-metric determination of bismuth (III) as it forms an anionic complexwith iodide, as tetraiodo bismuthate (III), which was best determined with CPC at490 nm. The detection limit was 65mg=L, with Bi having a molar absorptivity of1.20� 104 (Agrawal et al. 2004). Another report developed a spectrophotometric cata-lytic kinetic FIA method for the determination of nanogram amounts of copper (II)was based on the catalytic effect of copper on the reduction of azure B,f3-Methylamino-7-dimethyl-aminophenothiazin-5-ium chloride, CAS No. 531-55-5gby sulfide in a CTAB micellar system at 647 nm, with 9.2mg=L as the detection limitand 50–1600mg=L as the calibration range (Safavi et al. 2005). In another paper thereaction of indium with dithizone, f1-anilino-3-phenyliminothiourea, CAS No.60-10-6g in a SDS solvent system produced a red product that was detected at530 nm; using FIA eliminated the use of organic solvents. The linear calibration rangereported was 0.25–6.0mg=L with a molar absorptivity of 6.7� 103 (Memon, Ahmed,and Bhanger 2005). Zhang et al. (2006) reported copper (II)’s reaction with chromeazurol S, fMordant Blue 29, CASNo. 1667-99-8g as the basis for the FIA spectropho-tometric analysis in a borax buffer CTAB solution. This procedure’s detection limitwas 0.76 mg=L, and the calibration curve covered from 5–200 mg=L. Another analysisof copper (II) was also reported by Li, Zhang, and Zou (2007) in a FIA spectrophoto-metric method at 530 nm with a range of 10–210mg=L Cu2þ as it reacted with dibro-mohydroxyphenylfluorone f9-(3,5-dibromo-4-hydroxyphenyl)-2,6,7-trihydroxy-3H-xanthen-3-one, CASNo. 128529-34-0g in a CPBmicellar system with a detection limitof 0.98mg=L for copper (II). Between 5 and 400 mg=L zinc in seawater was determinedby a FIA spectrophotometric method at 630 nm in a CTAB borax buffered solutionusing salicyl-fluorone f2,6,7-trihydroxy-9-(o-hydroxyphenyl)-3-fluorone, CAS No.3569-82-2g as the metal complexation agent. Zinc’s detection limit was 1.5 mg=L(Long et al. 2006). A method for lead determination in the range 1.0–12.0mg=L witha detection limit of 0.027mg=L using 1,5-diphenylthiocarbazone fCAS No. 60-10-6gas the complexing agent in sulfuric acid and SDS for a FIA spectrophotometricmethod at 500 nm was reported (Ruengsitagoon, Chisvert, and Liawruangrath 2010).

Chemical luminescence methods have also been used for metal determination. Areview of fluorescence methods in the determination of aluminum, in Chinese appeared

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Table

2.Summary

ofmetalanalysismethods

Metal

Reagent

Surfactant

Technique

Detectionlimit

Reference

Ag(I)

diethyldithiocarbamate

SDS-preconcentration

FAAS

0.7mg

=L

Dadfarnia

andGohari2004

Ag(I)

salenA

SDS-preconcentration

FAAS

0.8mg

=L

Dadfarnia

etal.2006

Ag(I)

dithizone

TX-114–extraction

FAAS

0.7mg

=L

Dalaliet

al.2008

Bi(III)

iodide

CPC,CTAB

UV-V

is65mg

=L

Agrawalet

al.2004

Cd(II)

5-Br-PADAP

TX-114-extraction

ICP-O

ES

0.7mg

=L

J.Chen

2009

Cd(II)

HBDAP

SDS-preconcentration

FAAS

0.39ng=L

Kara

2009

Cd(II)

TAN

TX-114–extraction

FAAS

0.75mg

=L

E.L.SilvaandRoldan2009

Co(II)

thiocyan

ate

Tween-80

UV-V

is1.20mg=L

Pharr

andOstlund2003

Co(II)

PAR

TX-100

UV-V

is0.25mg=L

Pharr

etal.2004

Co(II)

luminol

Tween-80

chem

iluminescence

0.62mg

=L

H.LiandXie

2006

Co(II)

umbelliferone

CDEAB

chem

iluminescence

1.2mg

=L

Watanabeet

al.2009

Co(II)

luminol

CTAC

chem

iluminescence

0.1ng=L

Tak

ahashiet

al.2009

Co(II)

HBDAP

SDS-preconcentration

FAAS

7.5ng=L

Kara

2009

Co(II)

5-Br-PADAP

TX-114-extraction

ICP-O

ES

1.6mg

=L

J.Chen

2009

Co(II)

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

158ng=L

Y.LiandHu2009

Cr(III)

luminol

TX-114=SDS=TX-100

chem

iluminescence

0.5ng=L

Paleologoset

al.2003

Cr(III)

8-hyd

roxyquinoline

SDS-preconcentration

FAAS

0.16ng=L

Ahmadiet

al.2007

Cr(III)

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

92.6ng=L

Y.LiandHu2009

Cu(II)

azure

BCTAB

UV-V

is-kinetic

9.2mg

=L

Safaviet

al.2005

Cu(II)

chromeazurolS

CTAB

UV-V

is0.76mg

=L

Zhanget

al.2006

Cu(II)

DBHPfluorone

CPB

UV-V

is0.98mg

=L

H.Liet

al.2007

Cu(II)

luminol

Tween-80

chem

iluminescence

0.62mg

=L

H.LiandXie

2006

Cu(II)

luminol

CTAC

chem

iluminescence

5.5mg

=L

Uechiet

al.2004

Cu(II)

salenA

SDS-preconcentration

FAAS

0.3mg

=L

Dadfarnia

etal.2006

Cu(II)

salenI

SDS-preconcentration

FAAS

0.3mg

=L

Dadfarnia

etal.2005

Cu(II)

HBDAP

SDS-preconcentration

FAAS

3.2ng=L

Kara

2009

Cu(II)

5-Br-PADAP

TX-114-extraction

ICP-O

ES

1.3mg

=L

J.Chen

2009

Cu(II)

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

88.4ng=L

Y.LiandHu2009

Fe(II)

luminol

Tween-80

chem

iluminescence

0.62mg

=L

H.LiandandXie

2006

Fe(II),FE(III)

ferron

TX-114–extraction

FAAS

1.7mg

=L

Shakerianet

al.2009

(Continued

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Table

2.Continued

Metal

Reagent

Surfactant

Technique

Detectionlimit

Reference

Hg

KBr=KBrO

3TX-114cold

vapor

Atomic

Fluorescence

70ng=L

Cava-M

ontesinoset

al.2004

Hg

dithizone

TX-100–extraction

UV-V

is14mg

=L

Garridoet

al.2004

In(I)

dithizone

SDS

UV-V

is0.25mg=L

Mem

onet

al.2005

Mn(II)

luminol

CTAC

chem

iluminescence

0.5ng=L

Tak

ahashiet

al.2009

Mn(II)

HBDAP

SDS-preconcentration

FAAS

3.0ng=L

Kara

2009

Mn(II)

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

46.3ng=L

Y.LiandHu2009

Ni(II)

PAR

TX-100

UV-V

is0.25mg=L

Pharr

etal.2004

Ni(II)ethane

1,2-bis(salicylideneamino)

SDS-preconcentration

ICP-O

ES

78ng=L

Aref-AzarandMoghim

i2007

Ni(II)

HBDAP

SDS-preconcentration

FAAS

3.4ng=L

Kara

2009

Ni(II)

5-Br-PADAP

TX-114-extraction

ICP-O

ES

5.7mg

=L

J.Chen

2009

Ni(II)

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

212ng=L

Y.LiandHu2009

Pb(II)

1,5-diphenylthiocarbazone

SDS

UV-V

is27mg

=L

Ruengsitagoonet

al.2010

Pb(II)

salenI

SDS-preconcentration

FAAS

2.6mg

=L

Dadfarnia

etal.2005

Pb(II)

phosphate

O,O

-diethyldithio-

TX-114-preconcentration

ET-FAAS

16ng=L

Bai

andFan

2007

Pb(II)

HBDAP

SDS-preconcentration

FAAS

17.9ng=L

Kara

2009

Pb(II)

TAN

TX-114–extraction

FAAS

4.5mg

=L

E.L.SilvaandRoldan2009

Pb(II)

benzimidazole

2-guanidino

TX-114–extraction

FAAS

2.0mg

=L

Zah

ediet

al.2009

rare

earths

8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

72-500

ng=L

Y.LiandHu2010

rare

earths

none

TX-114-extraction

ICP-O

ES

41-448

ng=L

Y.LiandHu2010

Sb(III),dithiocarbamate

pyrrolidine

TX-114-extraction

ET-ICP-O

ES

90ng=LSb(V

)Y.Liet

al.2006

Tl(I)

dibenzo-18-crown-6

SDS-preconcentration

ET-FAAS

50ng=L

Asadoulahiet

al.2007

Tl(I),T1(III)

8-hyd

roxyquinoline

SDS-preconcentration

FAAS

2.5mg

=L

Dadfarnia,Assad

ollahi,

andShabani2007

V(V

)8-hyd

roxyquinoline

TX-114-extraction

ICP-O

ES

70.7ng=L

Y.LiandHu2009

Zn(II)

salicyl-fluorone

CTAB

UV-V

is1.5mg

=L

Longet

al.2006

Zn(II)

salenA

SDS-preconcentration

FAAS

0.47mg

=L

Dadfarnia

etal.2006

Zn(II)

HBDAP

SDS-preconcentration

FAAS

0.89ng=L

Kara

2009

Zn(II)

5-Br-PADAP

TX-114-extraction

ICP-O

ES

3.3mg

=L

J.Chen

2009

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in 2004 (P. Wang and Chen 2004). The luminol-hydrogen peroxide-chromium (III)reaction was the basis for the FIA chemiluminescence determination of Cr3þ in tworeported methods with luminol, f5-Amino-2,3-dihydro-1,4-phthalazinedione, CASNo. 521-31-3g.The first one reported a detection limit of 0.5 ng=L and an analyticalrange of 2–200ng=L. It used a mixed surfactant system composed of Triton X-114and SDS to attract the chromium cation to the micelle. Sodium sulfate was addedto produce a cloud point, and the cotton-based filter retained the thickened surfactantmixture to allow for both extraction and concentration of the chromium cation withinthe micelle. The retained surfactant was eluted off the column by a solution of TritonX-100 and bromide producing an enhancement of the chemiluminescence detection(Paleologos et al. 2003). The second paper reported a range of 3.1mg=L to 4.2mg=L,and the use of a citric acid-oxalic acid solution to eliminate interferences in this methodfrom Fe2þ, Co2þ, and Cu2þ when using a Tween-80 surfactant system. A detectionlimit of 0.62mg=L was achieved (H. Li and Xie 2006). Watanabe et al. (2009) reportedthe FIA chemiluminescence determination of cobalt (II) with umbelliferone,f7-hydroxy-chromen-2-one, CAS No. 95-35-6g in a solvent containing hydrogenperoxide and the cationic surfactant cetyldimethylethylammonium bromide. The limitof detection of 1.2mg=L was given (Watanabe et al. 2009).

A reverse micellar system was utilized in the FIA chemiluminescence analysisof cobalt and manganese in organic solvents, with the surfactant cetyl trimethylam-monium chloride (CTAC), in 1-hexanol-cyclohexane for a reaction with the luminolreaction. Detection limits of 0.1 ng=L (Co2þ) and 0.5 ng=L (Mn2þ) were obtainedwith linear ranges of 0.01–10 mg=L for cobalt and of 0.01–20 mg=L for manganese(Takahashi et al. 2009). A reverse CTAC system was used to determine copper(II) from its catalytic effect on the luminol reaction was reported in another method.The copper from copper-oxine, bis(8-quinolinolato)copper, was first extracted froman aqueous solution with chloroform and then separated in a flow system via mem-brane separation. Next, it was mixed with the CTAC chloroform-cyclohexane sol-ution whereupon the released copper affected the chemiluminescence of luminol.A detection limit of 5.5 mg=L and a calibration range up to 1.1mg=L was found(Uechi, Fujiwara, and Okamoto 2004).

Cold vapor atomic fluorescence determination of mercury in fish in an on-linemethod was established achieving a detection limit of 7 mg=kg of dried sample. In amixture of Triton X-114, potassium dichromate, and acid, the samples were injectedinto a flow system, sonicated, mixed with a solution KBr=KBrO3, and heated at50�C in a water bath. Then, the mercury was determined by cold vapor atomic fluor-escence. The reported detection limit was 70 ng=L (Cava-Montesinos et al. 2004).

The use of a complexation agent immobilized on a surfactant-coated aluminacolumn as a separation and preconcentration step has been the basis for severalmetal determinations using a wide variety of analytical methods including FAAS,and electrothermal atomic absorption spectroscopy (ET-AAS). The typical pro-cedure, as outlined by Ahmadi et al. (2007), involves column preparation by addingSDS just below its cmc to 1.5 g of alumina, then adjusting the pH to 2 with 4M HClbefore mixing for 10 minutes, washing with water followed by mixing the mixturewith the organic ligand for 15min., filtering, and adding it to the column. The anionhead group of the surfactant is attached by charge attraction to the solid alumina,and the hydrophobic tail now becomes the outside of the alumina particles thus

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allowing the hydrophobic organic ligand to be adsorbed onto the surface. In thismanner chromium (III) and total chromium were determined with an 8-hydroxyqui-noline fCAS No. 134-31-6g as the immobilized reagent on a SDS-coated aluminacolumn followed by flow injection atomic absorption spectrometry after elution witha 20% ethanol solution in 1.5M HCl. The detection limit was 0.16 ng=L with a linearcalibration range of 1.0–100 mg=L. Silver was determined using a similar methodwith diethyldithiocarbamate fsodium (diethylcarbamothioyl)sulfanide, CAS No.148-18-5g as the complexation agent from a pH 3-4 solution and immobilized onthe SDS coated alumina column. After collection, the complexed silver was washedoff with an injection of 250 mL of ethanol and analyzed by FAAS. An enrichmentfactor of 125 was achieved, and linear calibration was established as 5–100 mg=L witha detection limit of 0.7 mg=L (Dadfarnia and Gohari 2004). The simultaneous pre-concentration of silver, zinc, and copper on a SDS coated alumina column with salenA fN,N’-bis(salicylidene)ethylenediamine, CAS No. 94-93-9g as the complexingagent was released by the injection of 250 mL of 2M nitric acid followed by analysisby FAAS. The concentration factors reported were 125 for silver, 210 for zinc, and166 for copper. Detection limits were 0.8, 0.47, and 0.3 mg=L, respectively (Dadfarniaet al. 2006). Salen I f2,20-Ethylenebis(nitrilomethylidene)diphenol, N,N0-Ethylenebis(salicylimine)g was used in a similar manner for the determination of copper andlead using 2M nitric acid to elute the analyte for FAAS analysis. Enrichment factorsof 100 for copper and 75 for lead were discovered along with detection limits of 0.3and 2.6 mg=L, respectively (Dadfarnia et al. 2005). A method for thallium (I) analysiswith the SDS-alumina immobilized 8-hydroxyquinoline being eluted with 1Msodium thiosulfate and total thallium after the reduction of Tl3þ with hydroxylaminehydrochloride, fCAS No. 5470-11-1g was achieved for FIA-FAAS. A detection limitof 2.5 mg=L was claimed (Dadfarnia, Assadollahi, and Shabani 2007). The use ofdibenzo-18-crown-6 fCAS No. 14187-32-7g as the sequestering agent on surfactantcoated alumina, with analysis by ET-AAS after its removal by 2M nitric acid, wasalso devised as a method for thallium (I) analysis. Linear calibration of 0.1 to 20 mg=L with a detection limit of 50 ng=L was reported (Asadoulahi, Dadfarnia, andShabani 2007).

Lead determination with FIA enrichment was developed using a solution of0.03% TritonX-114 and the chelating agent O,O-diethyldithiophosphatefO,O-Diethyl S-[2-(ethylthio)ethyl] dithiophosphate, CAS No. 298-06-6g, whichwas trapped on a silica gel column and washed off with methanol after preconcen-tration for ET-AAS analysis. An enrichment factor of 21.6 and a linear range of0.2 to 35 mg=L with a detection limit of 16 ng=L were achieved (Bai and Fan2007). A Schiff’ base that was adsorbed on a surfactant coated activated carbonconical minicolumn was the foundation for nickel analysis by FIA-ICP-OES.The base used was 1,2-bis(salicylidene amino)ethane, f2,20-[1,2-ethanediylbis(nitrilomethylidyne)]bis-phenol, CAS No. 94-93-9g, and the nickel was washed offthe column by a 20% nitric acid solution. The concentration factor was 80 with adetection limit of 78 ng=L (Aref-Azar and Moghimi 2007). A cotton filled minicol-umn was used for the preconcentration of SDS and metals complexed with HBDAP,fN,N0-bis(2-hydroxy-5-bromo-benzyl)1,2-diaminopropane, CAS No. 375389-71-2g.It was used for the on-line FIA determination of several metals whose detectionlimits were in ng=L: 0.39 for Cd2þ, 7.5 for Co2þ, 3.2 for Cu2þ, 3.0 for Mn2þ, 3.4

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for Ni2þ, 17.9 for Pb2þ, and 0.89 for Zn2þ. A mixture of 30% (m=v) NaCl solution,the sample, SDS, HBDAP, and a borate buffer of pH 8.5 were pumped through thecotton filled minicolumn as the preconcentration step followed by elution with amixture of 0.5M nitric acid in 50% acetone (Kara 2009).

The multiple uses of CPE for metal determination were reviewed in 2005(Bezerra et al. 2005) and again in 2009 (Anthemidis and Miro 2009; Ojeda and Rojas2009; Baliza, Ferreria, and Teixeira 2009). Online CPE was combined with electro-thermal vaporization and analyzed by ICP-OES for antimony in environmental andbiological samples. The complexation of Sb3þ with pyrrolidine dithiocarbamatef1-Pyrrolidinecarbodithioic acid, ammonium salt, CAS No. 5108-96-3g, which ismore soluble in the TritonX-114 than the pH 5.5 buffer, was retained in acotton-packed microcolumn released by the addition of 100 mL of acetonitrile andthen analyzed. Total antimony was determined by Sb5þ being reduced to Sb3þ byL-cysteine and subtraction allowed for Sb5þ determination. The overall enhance-ment factor for Sb3þ was 872 with a detection limit of 90 ng=L (Y. Li, Hu, and Jiang2006). J. Chen et al. (2009) used the chelating reagent 5-Br-PADAP, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, f2-[2-(5-bromo-2-pyridinyl)diazenyl]-5-(diethylamino)phenol, CAS No. 14337-53-2g in water samples by FIA coupledICP-OES after cloud point extraction using TritonX-114 and elution with anethanol-nitric acid solution was used for the simultaneous determination of severalmetals with the following detection limits in mg=L: 0.7 for cadmium (II), 1.6 forcobalt (II), 1.3 for copper (II), 5.7 for nickel (II), and 3.2 for zinc (II). Reportedenhancement factors ranged from 8–18. Trace metals in seawater were investigatedusing FIA-ICP-OES with cloud point extraction with TritonX-114 without a chelat-ing agent. The enrichment factors were 14.9 for V5þ, 20.1 for Cr3þ, 16.2 for Mn2þ,17.5 for Co2þ, 18.8 for Ni2þ, and 15.9 for Cu2þ, and with detection limits of 70.7,92.6, 46.3, 158, 212, 88.4 ng=L for V5þ, Cr3þ, Mn2þ, Co2þ, Ni2þ, and Cu2þ respect-ively (Y. Li and Hu 2009). The same research group did a similar study of rare earthswith and without 8-hydroxyquinoline as a chelating agent with TritonX-114 precon-centration and FIA-ICP-OES analysis and 0.5M HCl as the eluent. The calibrationrange was 5–1000 mg=L for Ce, Er, Gd, Nd, Pr, Sm, Tb, and Tm and 2–1000 mg=L forthe other rare earths. Detection limits without a chelating agent were in ng=L: 295Ce, 159 Dy, 245 Er, 80.1 Eu, 500.5 Gd, 236 Ho, 151.1 La, 101.4 Lu, 295 Nd,407.7 Pr, 69.0 Sc, 509.5 Sm, 395 Tb, 361 Tm, 102.5 Y, 72.1 Yb, and with 8-hydro-xyquinoline as a chelating agent: 182 Ce, 99.1 Dy, 247 Er, 66.4 Eu, 448 Gd, 114Ho, 88.1 La, 78.2 Lu, 264 Nd, 367.7 Pr, 43.9 Sc, 409.5 Sm, 286 Tb, 255 Tm, 95.5Y, and 41.4 Yb (Y. Li and Hu 2010).

Trace amounts of complexed silver were determined on-line, utilizing CPEonto a cotton absorbent material and Triton X-114 followed by FAAS analysis.The extractions were accomplished from a 0.2M sulfuric acid solution with dithizoneacting as the complexation agent. The extraction was released from the minicolumnby the addition of tetrahydrofuran (THF). The detection limit reported was 0.7 mg=Lwith a linear range of 4–220 mg=L (Dalali, Javadi, and Agrawal 2008). Silva et al.determined lead and cadmium after FIA-CPE preconcentration by FAAS. Themetal ions were chelated with TAN, f1-[2-(2-thiazolyl)diazenyl]-2-naphthalenol,CAS No. 1147-56-4g, which migrated to the micelles of TritonX-114 from the pH8.5 buffered solution, and were subsequently concentrated onto a minicolumn

A REVIEW OF SURFACTANTS IN FLOW INJECTION ANALYSIS 2295

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(cotton or glass wool) and flushed off for determination by FAAS by the addition of3M HCl. The addition of barium ions as a masking agent to the sample solutionsminimized interferences from matrix effects. The enhancement factors rangedbetween 15.1 to 20.3, and detection limits were 4.5 mg=L for Pb and 0.75 mg=L forCd (E. L. Silva and Roldan 2009). A method for iron FIA-CPE-FAAS wasdeveloped using ferron f8-hydroxy-7-iodo-5-quinolinesulfonic acid, CAS No.547-91-1g, which complexed Fe2þ and Fe3þ into the micellar region of TritonX-114 at temperatures above 60�C, allowing for CPE with a detection limit of1.7 mg=L (Shakerian, Dadfarnia, and Shabani 2009). Lead was complexed with2-guanidino benzimidazole fN-1H-benzimidazol-2-yl-guanidine, CAS No.5418-95-1g at pH 8.5, and CPE accomplished with Triton X-114, collected on a cot-ton wool packed minicolumn and eluted with an ethanol and 0.2M nitric acid sol-ution then analyzed by FAAS. Zahedi, Dalali, and Yamini (2009) reported adetection limit of 2.0 mg=L with a calibration range of 6–600 mg=L. In another study,mercury was complexed with dithizone FIA for CPE on a cotton minicolumn with5% Triton X-100. The spectrophotometric determination occurred at 500 nm afterelution in 60�C water resulted in a range of 0.05–0.5mg=L, with a detection limitof 14 mg=L and an enhancement factor of 6. The CPE temperature of the TritonX-100 solution was lowered to 60�C by the addition of sodium sulfate to the solution(Garrido et al. 2004).

ENVIRONMENTAL ANALYSIS

The analysis of pollutants, herbicides, and pesticides have used chemilumi-nescence and fluorescence as the main methods for FIA investigations (summarizedin Table 3). The analysis of the phenylurea herbicide residues of diuron,f3-(3,4-dichloro-phenyl)-1,1-dimethylurea, CASNo. 330-54-1g, neburon, f1-butyl-3-3,4-dichlorophenyl)-1-methylurea, CAS No. 555-37-3g, isoproturon, f3-(4-isopropylphenyl)-1,1-dimethylurea, CAS No. 34123-59-6g, and linuron, f3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea, CAS No. 330-55-2g, combined FIA andfluorescence detection of the UV irradiated products of the herbicides in spiked tapwater samples. Both SDS and CTAC were used at their cmc levels to solubilize thereaction products and to enhance the fluorescence intensity, which exhibited linearcalibration over two orders of magnitude with a detection limit of 0.33–0.92mg=L(Irace-Guigand et al. 2005).

The broadleaf herbicide metsulfuron-methyl, f2-[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]-oxomethyl]sulfamoyl]benzoic acid methyl ester, CAS No.74223-64-6g, a sulfonylurea, was analyzed in environmental waters using a solidphase spectroscopy system and photochemical induced fluorescence. The fluores-cence detection of the UV irradiated product occurred when it was retained in a flowcell filled with ODS, octadecylsilane, silica gel coated with SDS with a detection limitof 0.14 mg=L. The SDS coated silica gel could be used for up to 500 cycles with a sam-ple through put of �34 analysis per hour The mobile phase contained 8mM SDS.The solid phase wash washed with a 30% methanol-water solvent with 8mM SDSbetween runs. The size of the injection volume of 1000 mL determined the analyticalrange of 0.5–175 mg=L; an injection volume of 300 mL had a range of 2.4–500 mg=L(Flores, Fernandez de Cordova, and Molina Diaz 2009).

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Table

3.Summary

ofenvironmentalanalysismethods

Analyte

Reagent

Surfactant

Technique

Detectionlimit

Reference

benzo[a]pyrene

H2O

2,

Tx-114extraction

chem

iluminescence

x40.2

enrichment

Songet

al.2006

bis(trichlorophenyl)oxalate

benzo[ghi]perylene

H2O

2,

Tx-114extraction

chem

iluminescence

x41.3

enrichment

Songet

al.2006

bis(trichlorophenyl)oxalate

benzo[k]fluoranthene

H2O

2,

Tx-114extraction

chem

iluminescence

x38.5

enrichment

Songet

al.2006

bis(trichlorophenyl)oxalate

cyan

ide

Ag

SDS-alumina

FAAS

60mg

=L

Dadfarnia,Assad

ollahi,Shabani,

Tam

adonet

al.2007

diuron

–SDS=CTAC

fluorescence

0.33mg=L

Irace-G

uigan

det

al.2005

Iodine

luminol

CTAC

UV-V

is50ng=L

Fujiwara

etal.2006

isoproturon

–SDS=CTAC

fluorescence

0.33mg=L

Irace-G

uigan

det

al.2005

linuron

–SDS=CTAC

fluorescence

0.33mg=L

Irace-G

uigan

det

al.2005

metsulfuron-m

ethyl

ODScolumn

SDS

fluorescence

0.14mg

=L

Floreset

al.2009

neburon

–SDS=CTAC

fluorescence

0.33mg=L

Irace-G

uigandet

al.2005

N-m

ethly

carbamates

o-phthalaldehyd

e,H

2O

2,

CTAB

fluorescence

screeningtest

Soto-C

hinchilla

etal.2005

bis(trichlorophenyl)oxalate

PAH’s

–Tergitol

HPLC-fluorescence

0.1-0.46mg

=L

C.F.Liet

al.2008

Se

EtrhodamineB,KSCN

Tween-60

UV-V

is30mg

=L

Xuet

al.2007

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The screening analysis for the pesticide family of N-methylcarbamates wasachieved in a multi-step process by off-line sample preparation by hydrolysis ofthe N-methylcarbamates to produce methylamine, which was then reacted with o-phthalaldehyde fCAS No. 643-79-8g to form a fluorescent derivative. The com-pound was then ready for injection. The hydrolysis solution consisted of a pH 9.3borate buffer and 20mM CTAB. The FIA detection used SDS-water containing apH 5.0 phosphate buffer as the solvent. The reaction products underwent aperoxy-oxalate chemiluminescence with hydrogen peroxide, whose intensity was pro-portional the total N-methylcarbamate concentration. The working solution of SDS,hydrogen peroxide, and bis(2,4,6-trichlorophenyl)oxalate, fCAS No. 1165-91-9g,was prepared fresh daily. The analysis was used as a screening test for carbamatepesticide levels based on current EPA regulations. The surfactant acted as a goodsolvent and prevented the degradation of the peroxyoxalate chemiluminescenceproduct that occurs in water (Soto-Chinchilla et al. 2005).

A reverse micelle chemiluminescence FIA method was developed for the deter-mination of iodine using luminol with 1-hexanol-cyclohexane solvent and CTAC asthe surfactant to eliminate to use of chlorinated organic solvents. The calibrationrange was 50 ng=L to 10 mg=L (Fujiwara et al. 2006). A UV-visible spectrophoto-metric method has been reported using micellar systems as solvents. Trace seleniumreacts with KSCN and Et rhodamine B in Tween-60 giving a product that is mon-itored at 605 nm. A linear range of 0.09–4.0mg=L with a detection limit of 30 mg=L was established (Xu, Dong, and Li 2007). The indirect determination of free cyan-ide in water samples and industrial waste water by FIA-FAAS was based on thereaction of cyanide with a silver complex discussed earlier in the Determinations ofMetals section of this review. This result was accomplished by using a microcolumnof SDS coated alumina with immobilized salen fN,N0-bis(salicylidene)-ethylenediamineg saturated with silver ions, and carrier solution of sodium hydrox-ide (10�5M). When the samples containing cyanide were injected, a release of silverions from the column resulted, which were then determined by FAAS. A linear rangeof 0.10 to 10mg=L with a detection limit of 60 mg=L was reported (Dadfarnia,Assadollahi, Shabani, Tamadon et al. 2007).

Cloud point extractions have been used for the preconcentration separation,the extraction, and the analysis of organic compounds as reviewed in Chinese (Shenand Shao 2006) and in English (Carabias-Martinez et al. 2000). Polycyclic aromatichydrocarbons were extracted with Tergitol 15-S-7, fCAS No. 68131-40-8g, a poly-glycol ether nonionic surfactant, and then were microwaved and ultrasonicallyassisted and analyzed using HPLC with a programmed fluorescence detector. Thedetection limit ranged from 0.101 to 0.456 mg=L, depending on the PAH used(C. F. Li et al. 2008). The advantages of on-line CPE compared to traditionalCPE were studied using benzo[a]pyrene and the peroxoxalate chemiluminescencedetection system. A cotton filled minicolumn collected Triton X-114 CPE phase thathad its cloud point temperature lowered by using sodium sulfate in the mobile phase.Elution was accomplished using pure acetonitrile. The method was based on thehydrogen peroxide oxidation of bis(2,4,6-trichlorophenyl)oxalate and the resultingchemiluminescence product. The enrichment factors reported were 40.2 for benzo[a]-pyrene, 38.5 for benzo[k]fluoranthene and 41.3 for benzo[ghi]perylene (Song et al.2006).

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DETERMINATION OF SURFACTANTS

Surfactants themselves have been the object of several studies. Thedetermination of tannery effluents for trace cationic surfactants was based on thediscoloration of Arsenazo (III) f3,6-bis[2-(2-arsonophenyl)diazenyl]-4,5-dihydroxy-2,7-Naphthalenedisulfonic acid, CAS No. 1668-00-4g in the presence ofKIO4 in aqueous HCl with both CTAB and CPB were studied. The two surfactantshad a range of 0.10 to 20mg=L; the detection limit was 80 mg=L (Tu et al. 2009). Thespectrophotometric determination of anionic surfactants based on their substitutionfor methyl orange in an ion pair with CPC at pH 5.0 was explored. A range of 0.5 to5.0mg=L with a detection limit of 34 mg=L was achieved (Lavorante et al. 2005).Light scattering of o-tolidine and anionic surfactants were measured at 400 nm usingboth FIA and sequential injection analysis. Dodecylbenzene sulfonic acid was usedas the reference surfactant; a linear range of 1.6 to 300mg=L was reported (March,Gual, and Frontera 2005). Potentiometric detection was used to determine anionicsurfactants (SDS and sodium tetrapropylenebenzene sulfonate) with on-line solidphase preconcentration using octadecylsilica chromatography disks in a FIA system.The eluent used was a 75% acetonitrile=water solution. An enrichment factor of 40was achieved for SDS, and a calibration range of 0.030mg=L to 2.66mg=L with adetection limit of 0.72 mg=L was established (Martinez-Barrachina and Del Valle2006). Determination with solvent extraction of cationic surfactants in pharmaceu-ticals and anionic surfactants in environmental water samples by FIA is the subjectof a review in Japanese (Ohno and Sakai 2004). Glycolipid biosurfactants, such aslipopeptide and phospholipid biosurfactants, in metabolites of microorganisms wereanalyzed by FIA after they reacted first with concentrated sulfuric acid and then withphenols for the spectrophotometric detection at 620 nm; results were linear from0mg=L to 300mg=L (Ning et al. 2004). Anionic surfactants, such as SDS, weredetermined in a FIA spectrophotometric method using cobalt (II) phthalocyaninefCAS No. 574-93-6g in dimethylsulfoxide. The absorbance at 658 nm decreased withincreasing surfactant concentration in the 2–30mg=L range maintaining a detectionlimit of 1mg=L. The same reaction was determined potentiometrically with a poly-meric membrane sensor with a linear range of 0.80 to 780 mM and a detection limit of0.56 mM (El-Nemma, Badawi, and Hassan 2009).

DETERMINATION OF PHARMACEUTICAL PRODUCTS

The use of chemiluminescence for the determination of drugs is very popular(a summary is given in Table 4). Using SDS, which acts as a stabilizer in the mobilephase, the peroxyoxalate chemiluminescence reaction allows for the determination offluorescence compounds or of those derivatized to be fluorescent. Sulphadiazine,used for urinary tract infections, f4-amino-N-pyrimidin-2-yl-benzenesulfonamide,CAS No. 68-35-9g was determined using bis(1,4,6-trichloro-phenyl)oxalatefCAS No. 1165-91-9g as the chemiluminescence precursor; imidazole fCAS No.288-32-4g as a catalyst; fluorescamine fCAS No. 38183-12-9g as the fluorescencetag; and hydrogen peroxide as the oxidant. Findings were reported linear over therange of 0.126 to 2.00mg=L with a detection limit of 379 mg=L for sulphadiazine(Lattanzio et al. 2008). The same peroxyoxalate chemiluminescence reaction withSDS in a pH 5.0 phosphate buffer was also used for the analysis of gentamicin,

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Table

4.Summary

ofpharm

aceuticalanalysismethods

Analyte

Reagent

Surfactant

Technique

Detectionlimit

Reference

alpinetin

–SDS

MEKC-U

V–

L.Liu

etal.2007b

aspartic

acid

o-phthalaldehyd

e,

mercaptoethanol

b-cyclodextrin=SDS

MEKC

1mM

Chenget

al.2005

benzoyl

peroxide

Wurster’sreagent

SDSorCTAB

UV-V

is52.8mg

=L

Pharr

andTomsyck

2009

berberine

–Tween-20

MEKC-U

V2–27mg

=L

L.Liu

etal.2007a

cardamonin

–SDS

MEKC-U

V–

L.Liu

etal.2007b

carvedilol

NaCl

SDS

fluorescence

1.47mg

=L

R.A.S.Silva

etal.2008

chloroquinePO

3�4

AuCl� 4,luminol

CTAC

chem

iluminescence

0.02mg

=L

Shi2008a

chlorpromazine

H2O

2Tween-80

UV-V

is6.4mg=L

Passoset

al.2008

cimetidine

K3Fe(CN) 6

Tween-80

chem

iluminescence

20mg

=L

X.Chen

2005

Dy

5-Br-PADAP

PONPE7.5

CZE-U

VVis

20mg

=L

Ortegaet

al.2004

fangchinoline

trim

ethoprim

Tween-20

MEKC

4.7mg=L

L.Liu,Liu,andChen

2005;

L.Liu,Chen

andHu2005

Fe

5-Br-PADAP

PONPE7.5

CZE-U

VVis

0.48mg

=L

Ortegaet

al.2004

gentamicin

bis(trichlorophenyl)oxalate,

fluorescam

ine,

H2O

2

SDS

chem

iluminescence

1.18ng=L

Fernandez-R

amoset

al.2006

granisetron

HCl

AuCl� 4,luminol

CTAC

40ng=L

Shi2008c

chem

iluminescence

jatrorrhizine

–Tween-20

MEKC-U

V22–27

mg=L

L.Liu

etal.2007a

novalgin

dim

ethylamino-

SDS

UV

Vis

44mg

=L

Weinertet

al.2007

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cinnamaldehyd

e

palm

atine

–Tween-20

MEKC-U

V22–27

mg=L

L.Liu

etal.2007a

perphenazine

H2O

2Tween-80

UV-V

is5.1mg=L

Passoset

al.2008

propantheline

Br

AuCl� 4,luminol

CTAC

40ng=L

Shi2008b

chem

iluminescence

ranitidine

HCl

AuCl� 4,luminol

CTAC

0.03mg

=L

Shi2009

chem

iluminescence

rhodamineB

–SDS

fluorescence

0.24mg

=L

Wang,C.C.,2008

sulphadiazine

bis(trichlorophenyl)oxalate,

fluorescam

ine,

H2O

2

SDS

chem

iluminescence

379mg

=L

Lattanzioet

al.2008

tetrandrine

trim

ethoprim

Tween-20

MEKC

3.3mg=L

L.Liu,Liu,andChen

2005;

L.Liu,Chen,andHu2005

thymolblue

titrations

carbethopendecinium

Br

UV-V

is20mg=L

Nem

covaet

al.2005

thymolblue

titrations

carbethopendecinium

Br

potentiometric

2.00g=L

Nem

covaet

al.2005

vitamin

Eiron(III)phenanthroline

SDS

UV-V

is0.86mg=L

Mem

onet

al.2004

vitamin

K3

-SDS

fluorescence

0.18mg

=L

Perez-R

uiz

etal.2004

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an aminoglycoside antibiotic, fCAS No. 1403-66-3g with imidazole as the catalyst.The micelles prevented the degradation of the product that occurs in water. Theestablished analytical range was 3.93–30mg=L with a detection limit of 1.18mg=L(Fernandez-Ramos et al. 2006).

The FIA fluorescence detection (kex¼ 340, kem¼ 410 nm) based on the on-linephotoreduction of menadione, vitamin K3, f2-methyl-naphthalene-1,4-dione, CASNo. 58-27-5g using SDS in the mobile phase over the 2.42 to 245 mg=L demonstrateda detection limit of 0.18 mg=L (Perez-Ruiz et al. 2004). FIA using SDS and fluores-cence detection (kex¼ 286, kem¼ 341 nm) with sodium chloride, which enhanced thesignal, was used for the analysis of carvedilol, a beta-blocker used in heart disease,f(�)-[3-(9H-carbazol-4-yloxy)-2-hydroxypropyl][2-(2-methoxyphenoxy) ethyl]-amine, CAS No. 72956-09-3g over the range of 0.41mg to 36.6 mg=L; it maintaineda detection limit of 1.47 mg=L (R. A. S. Silva et al. 2008).

The uses of reverse micelles forming in non-polar media have been coupledwith chemiluminescence in several instances. These studies are based on the reactionof an ion pair complex that forms with the cationic analyte and tetrachloroaurate(III), which reacts with luminol inside the reverse micelle of CTAC, cetyltrimethyl-ammonium chloride, where there are trace amounts of water. Chloroquinephosphate, an anti-malaria drug, fN0-(7-chloro-quinolin-4-yl)-N,N-diethylpentane-1,4-diamine, CAS No. 54-05-7g was analyzed by FIA in this manner from a dicho-lormethane cyclohexane solvent from a range of 1 mg–15mg=L with a detection limitof 0.02 mg=L (Shi 2008a). Propantheline bromide, an antimuscarinic, which can beused for hyperhidrosis fN-isopropyl-N-methyl-N-f2-[(9H-xanthen-9-ylcarbonyl)oxy]ethylpropan-2-aminium bromide, CAS No. 298-50-0g, was protonated and analyzedin the same manner from dichloromethane in the 1 ng=L to 10mg=L range and had adetection limit of 40 ng=L (Shi 2008b). Shi (2008c) also reported the analysis ofgranisetron hydrochloride, an antiemetic to treat nausea and vomiting follow-ing chemotherapy f1-methyl-N-((1R,3r,5S)-9-methyl-9-azabicyclo[3.3.1]nonan-3-yl)-1H-indazole-3-carboxamide, CAS No. 109889-09-0g, from dichloromethane by this FIAmethod over the range 1ng=L to 20mg=L and a detection limit of 40ng=L.

Using an n-octanol=cyclohexane solvent mixture, ranitidine hydrochloride,which is used in treatment of peptic ulcer disease and gastroesophageal refluxdisease fN-(2-[(5-(dimethyl-aminomethyl)furan-2-yl)methylthio]ethyl)-N-methyl-2-nitroethene-1,1-diamine, CAS No. 66357-35-5g, was determined via the same FIAchemiluminescence method in the 1 mg=L to10mg=L range, producing a detectionlimit of 0.03 mg=L (Shi 2009). The use of a potassium hexacyanoferrate(III), sodiumhydroxide reaction with cimetidine in a Tween-80 solution served as the basis for theFIA chemiluminescence detection from 100 ng=L to 0.10mg=L of cimetidine, sold asTagamet, used in the treatment of heartburn and peptic ulcers, f2-cyano-1-methyl-3-(2-[(5-methyl-1H-imidazol-4-yl)methylthio]ethyl)guanidine, CAS No. 51481-61-9gwith a detection limit of 20 mg=L (X. Chen 2005).

Simultaneous determination of dysprosium and iron in urine to monitor theelimination of dysprosium-based pharmaceuticals by CZE, capillary zone electro-phoresis, was mediated by micelles of the non-ionic surfactant PONPE 7.5,fpolyethyleneglycol-mono-p-nonylphenylether, CAS No. 26027-38-3g and the com-plexing agent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, f2-[2-(5-bromo-2-pyridinyl)diazenyl]-5-(diethylamino)-phenol, CAS No. 14337-53-2g. The on-line

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preconcentration step loaded the surfactant onto the cotton wool packed minicol-umn at pH 9.2 and then eluted it with acetonitrile into a sample vial, creating a200 fold enrichment for a 10mL urine sample. Detection of the chelated metals at585 nm resulted in detection limits for Dy of 0.20 mg=L and for Fe of 0.48 mg=L(Ortega et al. 2004).

The FIA spectrophotometric analysis of novalgin, a non-steroidal anti-inflammatory drug, fsodium [(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-yl)methylamino]methanesulfonate, CAS No. 68-89-3g at 510 nm after it reacts withp-dimethylaminocinnamaldehyde, fCAS No. 6203-18-5g to form a red product hadits sensitivity increased 5.6 times when SDS was used in the solvent. The reported lin-ear calibration was 0.48 to 9.7mg=L with a detection limit of 44 mg=L (Weinert et al.2007). The FIA spectrophotometric analysis of benzoyl peroxide at 612 nm usingWurster’s reagent, fN,N,N,N-tetramethyl-p-phenylenediamine, CAS No. 100-22-1gand a solvent system, including the surfactant SDS or CTAB, and cerium (IV) as acatalyst at pH 6.0 was investigated. The method was applied to the analysis of acnecream and flour with a linear calibration of 210 ng to 52.8 mg of benzoyl peroxide usinga 5.00 mL loop (Pharr and Tomsyck 2009).

The indirect determination of a form of vitamin E, a-tocopherol f(2R)-2,5,7,8-Tetramethyl-2-[(4R,8R)-(4,8,12-trimethyltridecyl)]-6-chromanol, CAS No. 59-02-9gby FIA in SDS micellar media using iron (III) 1,10-phenanthroline as an oxidantwas analyzed spectrophotometrically for the range of 5.2–401mg=L, producing adetection limit of 0.86mg=L (Memon et al. 2004). The FIA of rhodamine B dyefCAS No. 81-88-9g in cosmetics using a fluorescence detector and SDS in the mobilephase was studied. A linear range of 0.77 to 479 mg=L with a detection limit of0.24 mg=L was achieved (C. C. Wang, Masi, and Fernandez 2008). Spectrophoto-metric determination with thymol blue, fCAS No. 76-59-5g and potentiometricdetection methods were used in the FIA neutralization titrations of 10H-phe-nothiazine derivatives, S(C6H4)2NH, organic compounds that occurs in variousantipsychotic and antihistaminic drugs in cationic micellar solutions. The surfac-tant used was 3mM carbethopendecinium bromide, f(1-ethoxy-1-oxohexadecan-2-yl)-trimethylazanium bromide, CAS No. 10567-02-9g in a 0.1M KCl solution.The potentiometric range was 2.00–20.00 g=L, and the spectrophotometricrange was 20–500mg=L (Nemcova et al. 2005). Another analysis used thecolored free-radical that formed from the reaction hydrogen peroxide with twoantipsychotic drugs: chlorpromazine f3-(2-chloro-10H-phenothiazin-10-yl)-N,N-dimethyl-propan-1-amine, CAS No. 50-53-3g and perphenazine f2-[4-[3-(2-chloro-10H-phenothiazin-10-yl) propyl]piperazin-1-yl]ethanol, CAS No. 58-39-9g in aTween-80 solution was determined by FIA at 527 nm. Chlorpromazine was analyzedin water while perphenazine was studied in a micellar media. The detection limit was6.4mg=L for chlorpromazine and 5.1mg=L for perphenazine (Passos, Saraiva, andLima 2008).

Micellar electrokinetic chromatography (MEKC) is a modification of capillaryelectrophoresis with separation being accomplished by differential partitioningbetween micelles and the surrounding aqueous mobile phase buffer; it has beencoupled with FIA in several papers. Tetrandrine, a calcium channel blocker,f6,60,7,12-tetramethoxy-2,20-dimethyl-1 beta-berbaman, CAS No. 518-34-3g andfangchinoline f2,20-dimethyl-6,60,12-trimethoxy-(1-beta)-berbaman-7-ol), CAS

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No. 436-77-1g were analyzed in herbal medicines using trimethoprim, f5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine, CAS No. 738-70-5g as an internal stan-dard and Tween-20 as the surfactant. Enhancement factors reported were between6.8 and 8.9. The calibration range of tetrandrine and fangchinoline was 13.0 to172.7mg=L with a detection limit of 3.3mg=L for tetrandrine and 4.7mg=L for fang-chinoline (L. Liu, Liu, and Chen 2005; L. Liu, Chen, and Hu 2005).

Aspartic acid enantiomer analysis by online derivatization with o-phthalalde-hyde fCAS No. 643-79-8g and mercaptoethanol fCAS No. 60-24-2g were separatedwith b-cyclodextrin in a SDS buffer solution containing methanol. Recovery levelsbetween 1.0 to 6.0mM were reported (Cheng et al. 2005). The derivatized enantio-mers were UV-absorbing, and they were separated by MEKC. Three herbalmedicine components, isoquinoline alkaloids: berberine f5,6-dihydro-9,10-dimethoxy-Benzo[g]-1,3-benzodioxolo-[5,6-a]quinolizinium), CAS No. 633-66-9g,palmatine f2,3,9,10-tetramethoxy-5,6-dihydroisoquinolino[2,1-b]isoquinolin-7-ium),CAS No. 3486-67-7g, and jatrorrhizine f2,9,10-trimethoxy-5,6-dihydro-isoquinolino[2,1-b]isoquinolin-7-ium-3-ol), CAS No. 3621-38-3g were analyzed with theFIA-MEKC combination using Tween-20 as the surfactant. The technique employedcontinuous online stacking utilizing head-column-field, which amplified sample injec-tion with a 64-86 fold improvement in the detection sensitivity. The detection limitreported was 22-27 mg=L (L. Liu, Chen, and Hu 2007a). Cardamonin f(E)-1-(2,4-Dihydroxy-6-methoxyphenyl)-3-phenylprop-2-en-1-one), CAS No. 19309-14-9gand alpinetin f2,3-dihydro-7-hydroxy-5-methoxy-2-phenyl-4h-1-benzopyran-4-one),CASNo. 36052-37-6g fromAlpinia katsumadai Hayatawere analyzed by FIA-MEKCat 214 nm using a fused silica capillary column and an ethanol-SDS-sodium borate=phosphate buffered mobile phase (Liu, Chen, and Hu 2007b).

BIOCHEMICAL APPLICATIONS

A potassium periodate-manganese (II) sulfate reaction with troxerutin, f2-[3,4-bis(2-hydroxy-ethoxy)phenyl]-5-hydroxy-7-(2-hydroxyethoxy)-4-oxo-4H-chromen-3-yl 6-O-(6-deoxy-b-D-mannopyranosyl)-b-D-glucopyranoside, CAS No. 56764-99-9ga flavonol, exhibited chemiluminescence with enhancement in aTween-80micellar environment with an analytical range of 200 mg=L to 80mg=L, resulting ina detection limit of 70 mg=L (X. Chen 2006). Human serum albumin was studied bya reaction of fluorescein-HSA-sodium hypochlorite by FIA chemiluminescence,which exhibited signal enhancement in a CTAB surfactant system. It was believedthat the CTAB caused the structural change of the fluorescein from the quinone tothe spirolactone and that this enhanced the chemiluminescence of the fluorescein-HSAwhose linear range was 50mg=L to 24.0mg=L. The detection limit for this methodwas 30mg=L (Huang, Zhang, Liu et al. 2007). Similarly, fluorescein isothiocyanate-bovine serum albumin-hypochlorite complexes with ovoco-albumin and human serumalbumin in the place of BSA. These were analyzed by FIA chemiluminescence exhibit-ing increased signals in the presence of cationic surfactant system CTAB (Huang,Zhang, and Ci 2007). Another analysis for the determination of adenine in the range59ng=L to 0.395mg=L was achieved using luminol in a potassium dichromate alkalinemedia with the surfactant SDS fCAS No. 25155-30-0g in a FIA chemiluminescencedetermination. The reported detection limit was 33ng=L (L. Liu and Xue 2006).

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The cutinase activity based on the hydrolysis of p-nitrophenylbutyrate top-nitrophenol was monitored at 400 nm in a FIA system having absorbance valuesfrom 0.4 to 0.98. The mobile phase contained 50mM of a pH 7.0 phosphate buffer,0.43M THF, tetrahydrofuran, 0.55M p-nitrophenylbutyrate, and the mild biosurfac-tant sodium cholate fCAS No. 361-09-1g. Activity measurements made on-line com-pared favorably to those measured off-line (Almeida, Cabral, and Fonseca 2004).Cutinase activity was explored further utilizing expanded bed adsorption to recover,purify, and concentrate Fusarium solani pisi cutinase, secreted by a recombinant Sac-charomyces cerevisiae strain, directly from a whole fermentation culture prior to FIA.The same p-nitrophenyl-butyrate to p-nitrophenol FIA monitoring system was usedwith THF added to the phosphate buffer sodium cholate mobile phase for the studyof expanded bed adsorption experiments. The FIA system exhibited a variation coef-ficient of 2.3% compared to 8% by the off-line method (Almeida et al. 2006).Expanded bed adsorption was in another study with a FIAmicellar system to monitorcutinase activity in the separation of Saccharomyces cerevisiae (Fonseca et al. 2005).On-line salt induced CPE with a cotton packed column for the determination of totalserum bilirubin in the 5 to 120 mg=L range by chemiluminescence using the peroxyox-alate reaction was reported with a detection limit of 1.8 mg=L (Lu et al. 2007).

Future studies may develop the use of surfactants and CPE for the determinationof anions. The ability of a mixture of cationic and anionic surfactants to form twoliquid phases at low concentrations has not yet been put to any analytical advantage(Hinze and Pramauro 1993). Micellar systems are not widely reported for use inFIA liquid-liquid extractions, but they could be used that way. Amphiphilic ligands(containing an organic chelate with a long hydrocarbon chain) and nonionic alkylcrown ethers are two novel types of surfactants that may expand the possibilities forfuture analytical determinations. Surfactant-FIAs combined with other techniqueshave yet to be explored; these methods include ion exchange, wetting film extraction,extraction chromatography, and liquid phase microextractions. The use of detectorsthat are utilized for HPLC could also be investigated in combination with CPE tolower detection limits. Many of the existing applications of surfactants in analyticalchemistry have used surfactants and CPE, but they have not yet been applied to FIA.

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