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Finally, GC performance criteria need to be prescribed more precisely. For example, the choice of the capillary GC column and GC integration algorithms should be specified, and authenticated instrument calibration mixtures for analytes and internal standards should be issued with the samples. Scrupulous attention to sound analytical practices such as those recommended here could enable interlaboratory reproducibility to approach the 10-30% (lo) intralaboratory precision now observed in some of these participating laboratories.
ACKNOWLEDGMENT The following scientists and laboratories participated in both Duwamish I and I1 sediment interlaboratory comparisons: Rudolf Bieri, Virginia Institute of Marine Science; Paul Boehm, Energy Resources Co.; Isaac Kaplan, University of California, Los Angeles; John Laseter, University of New Orleans; James Payne, Science Applications, Inc.; and Robert Riley, Battelle Northwest Laboratories. Ronald Atlas, University of Louisville, John Farrington, Woods Hole Oceanographic Institution, Harry Hertz, National Bureau of Standards,Judy Lytle, Gulf Coast Research Laboratory, David Page, Bowdoin College, and David Shaw, University of Alaska, also participated in the Duwamish I intercomparison. Patrick Parker, University of Texas, also participated in the Duwamish I1 intercomparison. Valuable comments were offered by Keith Kvenvolden, U.S. Geological Survey, by Lawrence Thomas, Oregon State
1982,5 4 , 392-397
University, and by members of the ACS Subcommittee on Environmental Analytical Chemistry ( I ) .
LITERATURE CITED MacDougall, D.; Crummett, W. B. Anal. Chem. 1980, 52, 2242. Galler, S. R. NBS Spec. Pub/.( U . S . ) 1974, No. 409, 29. Farrlngton, J. W.; Teal, J. M.; Medeiros, G. C.; Burns, K. A,; Roblnson, E. A. Anal. Chem. 1978, 48, 1711. Wlse, S. A.; Chesler, S. N.; Guenther, F. R.; Hertz, H. S.; Hilpert, L. R.; May, W. E.;Parris, R. M. Anal. Chem. 1980, 52, 1828. Hilpert, L. R.; May, W. E.;Wlse, S. A,; Chesler, S. N.; Hertz, H. S. Anal. Chem. 1978, 50, 458. Brown, D.W.; Ramos, L. S.; Uyeda, M. Y.; Frledman, A. J.; MacLeod, W. D., Jr. A&. Chem. Ser. 1980, No. 785, Chapter 14. Farrington, J. W.; Tripp, B. W. ACS Symp. Ser. 1975, No. 78,Chap ter 15. Ramos, L. S.; Brown D. W.; Jenkins, R. G.; MacLeod, W. D., Jr. NBS Spec. Publ. ( U S . ) 1979, No. 579, 713. Gowan, R. “Statistical Evaluation of Interlaboratory Calibration for Hydrocarbons in a Duwamish Intertldal Sediment”; Appendix in MacLeod, W. D., Jr.; Krahn, M. M.; Piskur, F. T. “Quality Assurance Program for Trace Petroleum Component Analysis”; Annual Reports of Principal Investigators, 1981; NOAA/OMPA, Juneau, AK. Ramos, L. S.; Prohaska, P. G. J . Chromafogr. 1981, 277, 284. Farrlngton, J. W. Adv. Chem. Ser. 1980, No. 785, Chapter 1.
RECEIVED for review September 25,1981. Accepted November 24,1981.This study was sponsored by the Outer Continental Shelf Environmental Assessment Program of the National Oceanic and Atmospheric Administration with funds from the Bureau of Land Management. Reference to a company or product does not imply endorsement by the U.S. Department of Commerce to the exclusion of others that may be suitable.
Solvent Extraction-Spectrophotometric Determination of Anionic Surfactants with Ethyl Violet Shojl Motomlzu, Slgeru Fujlwara, Aklhlro Fujiwara, and Kyojl T6ei Department of Chemlstry, Faculty of Sclence, Okayama lJnlversi@, Tsushima-naka, Okayama-shi, Japan
Several catlonlc dyes were evaluated as reagents for the spectrophotometrlc determinatlon of anionic surfactants. of the dyes examlned, ethyl vlolet was the most useful reagent. By use of this dye, trace amounts of anlonlc surfactants could be extracted Into benzene and toluene In a slngle extractlon and determlned spectrophotometrlcally at 615 nm; the molar absorptlvlty was about 1 X I O 5 L mol-‘ cm-‘ and the absorbance of the reagent blank was 0.01. The method could be applled to the determlnatlon of parts-per-bllllon amounts of anlonlc surfactants In waters with satlsfactory results.
Almost all of the methods for the spectrophotometric determination of anionic surfactants depend on the formation of a salt (ion associate) when dye cation reacts with anionic surfactants. Methylene blue is one of the most frequently used cationic dyes ( I , 2). The methylene blue method, however, is very troublesome and its sensitivity is very low because of the small extractability of the ion associate of methylene blue with anionic surfactants. Recently, several studies for the development of a simpler and more sensitive method have been carried out. Taguchi et al. (3) used the cobalt complex cation of 2-(2-pyridylazo)-5-diethylaminophenol as the cationic reagent and extracted anionic surfactants into benzene. The molar absorptivity was 5.5 X lo4 L mol-l cm-l at 550 nm. In our laboratory, several kinds of cationic dyes, such as malachite green (4,methylene blue analogues (5), Bindschedler’s green
analogues (6), and the derivatives of l-alkyl(or aryl)-4-(4diethylaminopheny1azo)pyridinium cation (cationic azo dye) (7,8) were synthesized and examined. Of these, the dibutyl analogue of Bindschedler’s green was the most sensitive reagent. The molar absorptivity was 7.1 X lo4L mol-1 cm-l at 730 nm, but the reagent was not so stable and the color faded gradually. The derivative of the cationic azo dye, 1(4-nitrobenzyl)-4- (4-diethylaminophenylazo)pyridinium bromide (NDP), however, was a very stable reagent and reacted with anionic surfactants to form ion associates, which were extracted into chlorobenzene. The sensitivity of the method with NDP was somewhat low (molar absorptivity 6.1 x lo4L mol-l cm-l at 571 nm) and centrifugation was required in order to separate the phases after shaking. The authors studied the extraction behavior of the triphenylmethane dye cation with several anions (9). From the results obtained in their work and other works (I0-12),it is expected that anionic surfactants at the parts-per-billion level can be determined by solvent extraction-spectrophotometry and ethyl violet is the most useful reagent of the dyes examined, because of the large extractability of the ion associate with the anionic surfactant into nonpolar solvents such as benzene and toluene. In this paper, the authors report the very useful method for anionic surfactants, in which anionic surfactants react with ethyl violet to form ion associates and subsequently these ion associates are extracted into nonpolar solvents and the absorbance of the ethyl violet in the organic phase is measured.
0003-2700/82/0354-0392$01.25/00 1982 American Chemical Society
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Table I. The Extraction Constants for Several Anions and the Molar Absorptivities for Anionic Surfactants Extracted into Organic Solvents log Kexa
cationic dye pararosaniline crystal violet ethyl violet methylene blue
solventd
C1-0.4 -1.9 0.8 B -1.9 T
