Anal. Chem. 1983, 55, 1603-1605
experimental observable must be related (linearly, if possible) simultaneously to some property of the analyte and the environment (the eluent). It must be possible to change the environment while keeping the concentiration of the analyte and the property of thLe analyte the same. For this reason, some chromatographic method that allows a change of eluent is the simplest solution. Following the procedure here, the peak area is meaningful regardless of the change in actual separation conditions (different k's or different number of theoretical plates), as long as one can correlate the peaks in each chromatogram. The detector must be a true differential detector, so that the contributions of the pure environment can be used as the base line. Otherwise, one will end up subtracting two large numbers to detect the small change in the experimental observable, losing sensitivity and significance at the same time. The other common differential detector in LC is the absorption detector. It satisfies all of the conditions outlined above. To be adapted to this scheme, one must use at least two eluents with different molar absorptivities at the wavelength of interest (e.g., benzene and hexane at 254 nm). The difficulty is that when the highly absorbing eluent is used, so little light reaches the sensor of the detector that the normal electronics will not function. So, some redesign of the commercial UV absorption detector for LC must first be made. Then, it can be seen that mole fraction (rather than volume fraction) becomes the appropriate unlit for concentration. Technical problems not withstanding, the micropolarimeter for LC (IO) can be used in conjunction with optically active eluents, e.g., (f)3-mt~thylcyclohexanoneand a nonchiral analogue. The differential measurement is essentially accomplished by setting the appropriate mechanical null for the analyzer. There, weiglht fraction is the relevant unit. In gas chromatography, the two detection methods that fit this scheme are the gas density balance (11) and the thermal conductivity detector (12). The former is based on a very complicated and delicate design and has relatively large volumes and poor sensitivity. So, even though the weight and the molecular weight can both be determined by using our scheme, it is not likely to be of great value. The latter involves very well-developed instrumentation, but the dependence on
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molecular properties is very complicated. For low concentrations and molecular weights very different from that of the eluent, however, some approximations can be made to fit our scheme. Mole fraction is again the appropriate unit of concentration. The universal nature of its response is once again attractive. Work toward demonstrating some of these other concepts is in progress in our laboratory. Finally, it should be particularly interesting to apply this scheme to gel. permeation chromatography, where many eluents produce the same chromatogram. The molecular size information in the chromatogram can be used in conjunction with the volume fraction determined here to give a count of the molecules. This concept should work even for poorly resolved chromatograms (fairly continuous distribution of molecular sizes), by using eq 16 for each well-defined "slice" of the chromatogram. In the characterization of polymers or of fossil fuels, this is valuable new information. All these can be performed by using analytical scale LC, with instrumentation that is available in most analytical laboratories.
LITERATURE CITED (1) Lovelock, J. E.; MagQS, R. J.; Adlard, E. R. Anal. Chem. 1971, 43, 1962- 1965. (2) Lovelock, J. E. J. Chromatogr. 1974, 99,3-12. (3) Hirschfelder, J. 0.; Curtlss, C. F.; Bird, R. 8. "Molecular Theory of Gases and Liquids"; Wiley: New York, 1964; pp 852-871. (4) Yeung, E. S. I n "Advances in Chromatography"; Giddlngs, J. C., Grushka, E., Brown, P. R., Eds.; Marcel Dekker: New York, 1983. (5) Woodruff, 5. D.; Yeung, E. S. Anal. Chem. 1982, 54, 1174-1178. (6) Woodruff, S. D.;Yeung, E. S. Anal. Chem. 1982, 54, 2124-2125. (7) Skoog, D. b . ; West, D. M. "Principles of Instrumental Analysis", 2nd ed.;W. A. Saunders: Phlladelphia, PA, 1980; p 374. (8) "CRC Handbook of Chemistry and Physics"; Weast, R. C., Astle, M. J., Eds.; CRC Press: Boca Raton, FL, 1978. (9) Snyder, L. R. J. Chromatogr. Sci. 1978, 16, 223-234. (IO) Yeung, E. S.; Steenhoek, L. E.; Woodruff, S. D.; Kuo, J. C. Anal. Chem. 1980, 52, 1399-1402. (11) Martin, A. J. P.; James, A. T. Blochem. J. 1958, 63, 138-143. (12) Llttlewood, A. B. Nature (London) 1959, 164, 1631-1632.
RECEIVED for review December 3,1982. Accepted May 9,1983. R.E.S. thanks the Dow Chemical Co. for a research fellowship. The Ames Laboratory is operated for the U S . Department of Energy by Iowa State University under Contract No. W-7405-eng-82. This work was supported by the Office of Basic Energy Sciences.
Determinatiion of Selenium in Marine Sediments by Gas Chromatogiraphy with Electron Capture Detection K. W. Michael Slu" and Shier S. Borman
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Division of Chemistry, National Research Council of Canada, Ottawa, Ontario, Canada, K7A OR9
Selenium concentrations in marlne sediments were determined by gas chromatography with electron capture detection. The sedlments were dissolved in an acid mixture. Selenium was converted lnto ~i-nitrop~azrse~eno~, extracted Into toluene, and introduced Into the chromatograph. The detection limit was 0.2 pg alf Se Injected or 20 ng of Se/g of sediment. The standard deviation was about 7%.
1,2-Diaminobenzene (0-phenylenediamine) and its derivatives react selectively and quantitatively with selenium(1V) lNRCC 21290.
to form piazselenols that are both volatile and stable. Trace levels of selenium in materials as diverse as plant and animal tissues, metals, and natural waters have been determined success full^ as piazselenols by means of gas chromatography with electron capture detection. These analyses have been reviewed by T6ei et al. (2). No work on sediments or geological materials, however, has been reported in the literature. This paper describes the determination of selenium as 5-nitropiazselenol in marine sediments.
EXPERIMENTAL SECTION A Varian Aerograph Model 1200 gas 63Ni electron capture chromatograph equipped with a T~~~~~ detector (ECD) was used. The column was a 2-m borosilicate tube packed with 3% OV-225 on Chrornosorb W, SO/lOO mesh. It was Instrumentation.
0003-2700/83/0355-1603$01.50/0 Published 1983 by the American Chemical Soclety
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 9, AUGUST 1983
normally kept at 200 "C. Nitrogen (
