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since only selected ions are monitored. When complex mixtures are analyzed by SIM GC/MS, there is indeed the possibility that other compounds present in the sample might interfere with the ions being monitored. However, if the samples should originate from the same source as was in the case of our study (e.g., core samples from soil columns; leachate samples collected over a period of time from the same or similar soil columns), then possible interferences can be identified from the full-scan GC/MS data on selected samples. Furthermore, additional ions could be monitored that would help in the identification process. The fact that stable-labeled isotopes are being monitored simultaneously with the naturally abundant compounds helps in the identification process since the difference in retention time of the stable-labeled isotope and that of the naturally abundant compound remains constant during sample analysis. In contrast with data obtained in our laboratory for the same compounds using gas chromatography with nitrogen/ phosphorus detection (GC/NPD) and electron capture detection (GC/ECD), it appears that the GC/MS procedure provides better accuracy and precision and comparable sensitivities (8). The difficulty in the gas chromatographic analysis with element selective detectors is that atrazine and diazinon have to be analyzed by GC/NPD, while lindane and pentachlorophenol require analysis by GC/EC. Moreover, stable-labeled isotopes cannot be used since they are not resolved from the naturally abundant compounds. The lack of specificity of the SIM GC/MS technique presented here turns out to be a real advantage for quantitative work since it not only eliminates sample cleanup but has proven to be more precise than the standard procedure that uses an internal
standard spiked into the sample extract immediately prior to analysis.
ACKNOWLEDGMENT The authors thank Ron Hites and Greg Jungclaus for reviewing the manuscript and Marion Weissman for editorial work. Registry No. Atrazine, 1912-24-9; lindane, 58-89-9; pentachlorophenol, 87-86-5; diazinon, 333-41-5; water, 7732-18-5.
LITERATURE CITED (1) Colby, B. N.; Rosecrance, A. E.; Colby, M. E. Anal. Chem. 1981, 53. 1907-191 1. (2) “Method 1625 Revision B- Semlvolatile Organic Compounds by Isotope Dilution GC/MS”; Environmental Protection Agency, Fed. Regist. 1084, 4 9 , 184-198. (3) Ingram, L. L., Jr.; Mc Glnnis, G. D.; Parlkh, S.V. Anal. Chern. 1970, 51, 1077-1078. (4) Klein, E. R.; Klein, P. D. Biorned. Mass Spectrom. 1970, 6 , 515-545. (5) Pollard, J. E.; Hern, S.C. Environ. Toxicol. Chem. 1985, 4 , 361-369. (6) Hern, S.C.; Beck, F. P., Jr.; Pollard, J. E. “A Field Test of the EXAMS Model in an Industrial Waste Pond. EPA 600/X-83-034. U.S. Envlronmental Protection Agency, ORD, EMSL, Las Vegas, NV. (7) Lopez-Avila, V.; NicOll, G.; Hellier, W.; Taylor, J. H.,Jr.; Hern, S. C.; Beck, F. P., Jr.; Pollard, J. E. “Analysis of Environmental and Dosed Samples of Water and Sediment from a Controlled Access Pond”; paper presented before the Division of Environmental Chemistry, American Chemical Society, Seattle, WA, April 1983. ( 8 ) Lopez-Avila, V.; Hirata, P.; Kraska, S.;Flanagan, M.; Taylor, J. P., Jr., “Analysis of Water and Soil Samples from Lysimeter Columns (2-meter columns)”; EPA Contracts 68-03-3 100; 68-03-3226. Final Report for US. Environmental Protection Agency, ORD, EMSL, Las Vegas, NV, Feb 1985, 303 pp.
RECEIVED for review April 17,1985. Accepted July 22,1985. Support for this research was pyovided by the U S . Environmental Protection Agency, Contract No. 68-03-3100 and 6803-3226.
Determination of Methylthio-Substituted Polychlorinated Aromatic Compounds Using Gas Chromatography/Mass Spectrometry Hans-Rudolf Buser Swiss Federal Research Station, CH-8820 Wadenswil, Switzerland
The preparatlon of small quantlties of methylthlo-substltuted polychlorlnated benzenes, blphenyls, certain dlbenzo-p -dioxins, and dlbenrofurans and their analysls by gas chromatography/mass spectrometry (GC/MS) using dlff erent ionization technlques (EI, CI, and NCI) Is descrlbed. The novel synthesis method Involves y Irradiation of the polychlorlnated parent compounds In dlmethyl dlsulflde (DMDS) and results In dlsplacement of a CI substituent by a CH,S group. Thls fast and simple procedure leads to small but, for GC/MS analysls, sufflclent quantltles of these potential environmental and blological metabolltes. Marked dlfferences were observed in the E1 and NCI mass spectra among various CH,S-derivatlzed PCB Isomers (MeS-PCBs). The formatlon of M--CH, Ions (sulfide anions) is characterlstlc In NCI for most of these compounds.
Methylthio (CH3S-, MeS-)-substituted compounds are environmental and biological metabolites of polychlorinated compounds like the benzenes (PCBzs), the biphenyls (PCBs), 0003-2700/85/0357-2801$01.50/0
and very likely also of the dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) (for structures see Figure 1). Methylthio-substituted polychlorinated benzenes (MeS-PCBzs) and biphenyls (MeS-PCBs) or their oxygenated analogues (methyl sulfoxides, CH,SO-, and methyl sulfones, CH3S02-) have been found in aquatic and mammalian species (1-4) and in humans (5). These sulfur-containing metabolites are either directly formed in the environment or formed via glutathion and mercapturic acid conjugates in biological systems (6). Global pollution with some polychlorinated aromatics, especially with PCBs, has resulted in restrictions of their use; there is considerable interest in the environmental fate and metabolism of these compounds. MeS-PCBs also interfere in ultratrace analyses of PCDDs and PCDFs in sediments (7). The toxicological significance of these metabolites so far is largely unknown. Environmental analyses require reference and standard compounds. Synthesis methods for some CH&substituted polychlorinated aromatics are known (2,8). These methods are usually laborious and time-consuming, involve extensive isolation and purification, and lead to individual compounds. 0 1985 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 14, DECEMBER 1985
Table I. MeS-PCBzs from Reaction of PCBzs with DMDS and y Irradiation PCBz reacted hexa-CBz penta-CBz 1234-tetra-CBz 1235-tetra-CBz 1245-tetra-CBz
elut temp 170.4 160.3 149.9 143.3 132.1 138.3 126.4 137.1
MeS derivative"** isomer assignment MeS-penta-CBz MeS-2345-tetra-CBz MeS-2346- and MeS-2356-tetra-CBzd MeS-234-tri-CBz MeS-236-tri-CBz MeS-235-tri-CBz MeS-246-tri-CBz MeS-345-tri-CBze MeS-245-tri-CBz
Mf
E1 data' -35 -46
-50
-59
7
15
88
3
9
3 3
0.3 100 0.3 100
9
3
0.1 100
2
2
4 3
3
5 5
8 1
4
1 100
