8O

6O

o 40 .ID

20

o

G

~ 3

C - - 2

1

0

0

(b)

o o

o o

o

o o

0 0

0

0

0

0

(a) S

S R

3

o o o o o

A

10 30 50 70 90

T e m p e r a t u r e / ° C

FIG. 4. Temperature dependencies of the integrated band intensities of the second (a) and first (b) overtones of the OH stretching mode for the monomeric form of Z-9-octadecen-l-ol. (~) Data from the raw spectra (after density correction); (A) data from the difference spectra.

Fig. 4b. The intensit ies in bo th Fig. 4a and 4b increase with increasing t e m p e r a t u r e in the same way.

In the present s tudy results based on bo th the second and first over tone seem to be reliable. Both the second and first overtones of the O H stretching mode of the monomer ic form can p robab ly be used to moni tor the spectra l changes. However, the use of the second over- tone might be more convenient because one can deter- mine accurate in tegra ted intensi ty in an easier way.

C O N C L U S I O N

The presen t pape r demons t ra t e s t ha t the second over- tone of the OH st re tching mode of the monomer ic form of Z-9-0ctadecen- l -o l in pure liquid is very useful for probing the t e m p e r a t u r e - d e p e n d e n t change in the in- t egra ted intensit ies, which is re lated to the dissociation of hydrogen-bonded alcohols. More thorough N I R stud- ies of the s t ruc ture and t he rm odynam i c proper t ies of alcohols are now in progress in our group and will be repor ted soon.

1. M. Iwahashi, N. Hachiya, Y. Hayashi, H. Matsuzawa, M. Suzuki, Y. Fujimoto, and Y. Ozaki, J. Phys. Chem. 97, 3129 (1993).

2. M. Iwahashi, Y. Hayashi, N. Hachiya, H. Matsuzawa, and H. Ko- bayashi, J. Chem. Soc. Faraday Trans. 89, 707 (1993).

3. M. A. Czarnecki, Y. Liu, Y. Ozaki, M. Suzuki, and M. Iwahashi, Appl. Spectrosc. 47, 2162 (1993).

4. B. G. Osborne and T. Fearn, in Near In[rared Spectroscopy in Food Analysis (John Wiley & Sons, New York, 1986), p. 21.

5. Near-Infrared Technology in the Agricultural and Food Industries, P. Williams and K. Norris, Eds. (American Association of Cereal Chemists, St. Paul, Minnesota, 1990), p. 17.

6. A. S. Banana, and P. R. Griffiths, J. Near Infrared Spectrosc. l, 13 (1993).

7. V. Zanker, Z. Phys. Chem. 200, 250 (1952).

Comment on a "Simple and Efficient Method to Eliminate Spike Noise from Spectra Recorded on Charge-Coupled Device Detectors"

W I E L A N D H I L L Institut fEr Spektrochemie und angewandte Spek- troskopie (ISAS), P.O. Box 101352, 44013 Dortmund, Germany

Index Headings: Computer applications; Raman spectroscopy.

I N T R O D U C T I O N

Recently, Takeuch i et al. proposed a simple, so-called " robus t s u m m a t i o n " me thod for the efficient e l iminat ion of spike noise f rom charge-coupled device (CCD) data. 1 In their paper , robust s u m m a t i o n was shown to be ad- vantageous in compar ison to median filters, which had been occasionally employed to remove spikes f rom da ta recorded with CCD detectors. 2

In our opinion, miss ing-point fitting is the mos t ad- vanced me thod for spike removal . 3-5 Even the a lgor i thm by Phil l ips and Harr i s 3 is superior to the use of median filters and robus t s u m m a t i o n with regard to several fea- tures.

D I S C U S S I O N

Miss ing-point correct ion of spikes is based on a com- parison of measured values with es t imates calculated f rom a n u m b e r of neighboring da ta points within the same spec t rum or within successively recorded spectra. The point in question, as well as identified neighboring spikes, is deleted for the calculation of these est imates . By this a lgori thm, accurate es t imates are ob ta ined and can be used for efficient spike correction.

Robus t s u m m a t i o n is based on a compar ison with a single neighboring value measured on the t ime axis. In compar ison to miss ing-point fitting, this principle has the d isadvantages descr ibed below.

T h e s t andard deviat ion of the measured neighboring values is general ly larger t han t ha t of miss ing-point es- t imates . This factor leads to less reliable spike identifi- cation. Consequent ly , a higher propor t ion of unspiked da ta points need to be "correc ted ."

Generally, it is unknown whether the consecutively recorded spec t ra contain exact ly the same spectral in- formation. The proposed scaling, using the total in tensi ty of each spec t rum, 1 compensa tes for in tensi ty f luctuations due to laser instabil i t ies or changing adjus tments . Other dis turbances, such as changing s t ray room light, changing fluorescence background due to a degradat ion of fluo- rescent impuri t ies , or imperfec t beam point ing onto an inhomogeneous sample, m a y fur ther seriously influence the resul ts of the spike correct ion by this method. Fur-

Received 19 March 1993; revision received 18 June 1993.

Volume 47, Number 12, 1993 0~3-7028 /93 /4712-217152 .00 /0 APPLIED SPECTROSCOPY 2171 © 1993 Society for Applied Spectroscopy

thermore, spike intensities are included in the calcula- tion of the total intensities used for the scaling?

Robust summation is less successful for higher spike densities. Takeuchi et al. consider two measurements with 30 spikes per 1152 data points in each of these spectra. 1 In this example, the probability of two spikes occurring at the same channel of two successive record- ings is about 7 x 10 -4. If we consider the total number of data points in such a spectrum, the probability of the existence of one or more doubly spike-contaminated channels within two recordings is 0.54. With the appli- cation of a 9-point polynomial fitting with up to four missing points to a single l152-point measurement with a spike probability of 0.05, the probability of the exis- tence of noncorrectable points is only approximately 0.02. 4

Spike correction using multiply measured spectra has to be applied to data with spectral features with a half- width close to or smaller than the width of the spikes, which is typically one to three data points for the whole spike. In this case, the use of a multiple missing-point fitting algorithm should be preferred, as well, because of the more accurate estimates and the better performance at higher spike probabilities of this method in compar- ison to robust summation.

One advantage of robust summation for spike correc- tion seems to be its rather simple algorithm. However, the application of the elaborated multiple missing-point algorithm is also straightforward, and computation times between 1.2 and 0.25 s per spectrum with 1021 data points were reached with this algorithm on an AT com- patible computer. 4

ACKNOWLEDGMENTS

The financial support by the Ministerium/fir Wissenschaft und For- schung des Landes Nordrhein-Westfalen and the Bundesministerium for Forschung und Technologie is gratefully acknowledged.

1. H. Takeuchi, Sh. Hashimoto, and I. Harada, Appl. Spectrosc. 47, 129 (1993).

2. J. J. Baraga, M. S. Field, and R. P. Rava, Appl. Spectrosc. 46, 131 (1992).

3. G. R. Phillips and J. M. Harris, Anal. Chem. 62, 2351 (1990). 4. W. Hill and D. Rogalla, Anal. Chem. 64, 2575 (1992). 5. W. Hill and D. Rogalla, in Proceedings o / t h e 13th International

Con/erence on Raman Spectroscopy, W. Kiefer, M. Cardona, G. Schaack, F. W. Schneider, and H. W. SchrStter, Eds. (J. Wiley & Sons, Chichester, 1992), p. 1100.

Time-Resolved Laser-Induced Fluorescence Studies of Uranium/Sodium Dodecyl Sulfate Interactions

C H R I S T O P H E M O U L I N , * P A S C A L R E I L L E R , C A T H E R I N E BEAUCAIRE, and D A N I E L L E M O R D A N T CEA/DCC/DPE/SPEA/SPS/Labora to i re de Spec- troscopie Laser Analytique, 91191 Gi/ sur Yvette Ce- dex, France (C.M., P.R.); CEA/DCC/DSD/SCS/Labo- ratoire de Chimie A n a l y t i q u e en So lu t i on et d'Hydroggochimie. BP 6, 92265 Fontenay-aux-Roses Cedex, France (C.B.); and Universitg Pierre et Marie Curie (PARIS VI), Laboratoire d'Energdtique et Rdactivitd aux Interfaces, 8 rue Cuvier, 75005 Paris, France (D.M.)

Index Headings: Laser-induced fluorescence; Micelles; Quenching; Ura- nium.

INTRODUCTION

Time-Resolved Laser-Induced Spectrofluorometry (TRLIS) is a very sensitive and selective technique for uranium(VI) (U022÷) determination based on laser ex- citation followed by temporal resolution of the fluores- cence signal. 1-4 This analytical technique has been used for several years for uranium analysis in various matrices in the nuclear fuel cycle, in the environment, and in the medical field) -12 Limits of detection (LODs) for uranium are now lower than the ng/L range, and trends are leading towards direct analysis for on-line analysis via fiber op- tics and optode in the above fields. 13-15 However, aside from elementary analysis, TRLIS possesses an interest- ing characteristic, namely, its capability of giving both spectral information with the fluorescence spectrum (wavelength shifts, peaks ratio modifications) and tem- poral information with the fluorescence lifetime (char- acterization of the molecular environment). These fea- tures have been used to s tudy the interact ion (complexation, quenching, energy transfer) between U022+ and ions (Fe 2÷, Ag ÷, CI-, etc.) 16-1s or organic mol- ecules, 19 but very few investigations have been carried out with surfactants and uranium. 2°,21 Surfactants are organic compounds which possess both a polar or ionic head group and a nonpolar tail. Depending upon the nature of the head group, they can be classified as cat- ionic, anionic, or nonionic surfactants. When the surfac- tant is present at concentrations greater than its critical micellar concentration (CMC), aggregates called micelles are formed, into which organic compounds are solubi- lized. Micelles composed of ionic surfactants exhibit a high surface charge, and counter ions (ions of opposite charge to the surfactant) will bind to the surface of the aggregate.

Received 20 April 1993; revision received 27 May 1993. * Author to whom correspondence should be sent.

21'72 Volume 47, Number 12, 1993 0003-7028/93/4712-217252.00/0 APPLIED SPECTROSCOPY © 1993 Society for Applied Spectroscopy