Anal. Chem. 1987, 59, 913-917
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Quantitation of Toxaphene in Environmental Samples Using Negative Ion Chemical Ionization Mass Spectrometry Deborah L. Swackhamer,' M. Judith Charles,2and Ronald A. Hites* School of Public and Environmental Affairs a n d Department of Chemistry, Indiana University, Bloomington, Indiana 47405
A method for quantltatlng toxaphene in envlronmental samples uslng methane negatlve Ion chemical ionization ( N I C I ) mass spectrometry In the selected Ion mode Is given. N I C I Is highly selectlve and sensltlve for measuring toxaphene. Thls method monltors Ions from each of the homologue groups in the toxaphene mMure havlng 6 to 10 chlorlnes correspondlng to the M- or the (M - Cl)- ion clusters ( m / z 340, 341,342, 343, 375, 377, 411, 413, 447, 449). Additional Ions are monltored to correct for interferences from Chlorinated pestlcldes ( m / z 336, 338, 371, 373, 376, 412, 444, 448). Quantitation Is done relatlve to an internal standard, 2,2',3,4,4',5,6,6'-octachlorobiphenyl ( m / z 428 and 430). The N I C I response was h e a r over 4 orders of magnitude, and the detection llmlt was 75 pg. Thls method Is accurate and reproducible for measuring toxaphene In the presence of a major interferent, technical chlordane. The method is successful at measuring toxaphene In complex environmental matrices such as fish, and It can also be used to evaluate the changes in the relatlve homologue dlstrlbutlon that may have resulted from environmental transforrnatlons.
Toxaphene is a complex mixture of chlorinated camphene derivatives. It is produced by the controlled chlorination of (B) via camphene (A) forming (2-exo)-2,10-dichlorobornane a Wagner-Meirwein rearrangement (1). This reaction goes on to yield a complex mixture of substituted polychlorintited compounds, primarily bornanes (e.g., C) and bornenes (e.g., D).
Toxaphene was first introduced as a broad spectrum insecticide in 1945. Since that time, it has been used extensively throughout the world (40-100 million pounds/year) to kill insects that attack cotton, soybeans, and peanuts and to kill parasites on cattle (2, 3). For a limited time in the 1960s, Present address: Environmental and Occupational Health, School of Public Health, 420 Delaware St., SW, University of Minnesota, Minneapolis, MN 55455. *Present address: California Public Health Foundation, P.O. Box 520, 2151 Berkeley Way, Berkeley, CA 94704.
toxaphene was used to kill fish in lakes in Canada and the U.S. ( 4 ) . Due to its environmental persistence (half-life = 0.2-10 years in soil) and its toxicity (5),the use and production of toxaphene have decreased since the mid-l970s, and the United States drastically limited its use in 1983 ( 4 ) . Toxaphene, however, continues to be found in air, rain, biota, and sediments in areas far removed from sites of application ( 4 , 6-8). Thus, further studies are needed to examine the transport and environmental behavior of toxaphene in the environment. These studies require a quantitation method that is sensitive and selective for toxaphene. Thus, we have developed a method using electron capture negative ion chemical ionization (NICI) mass spectrometry. Toxaphene is difficult to quantitate because it is a poorly characterized mixture of more than 670 compounds, primarily polychlorinated bornanes (CloHls-,C1,) (9-1 1). The components in the toxaphene mixture elute over a wide range of GC retention times and are not completely resolvable even by high-resolution GC columns. For example, a chromatogram of a toxaphene standard is shown in Figure 1. Note that there are less than 100 resolved peaks, suggesting that most peaks contain multiple compounds. The retention times of common coeluting interferences such as PCBs, heptachlor, dieldrin, DDT, DDE, technical chlordane, octachlorostyrene (OCS), and mirex are indicated. Many interfering compounds can be eliminated by adsorption column chromatography prior to GC (12-15). Unfortunately, tlie addition of any cleanup procedure requires time, reduces recoveries, causes poor reproducibility, and thus, compromises accuracy and sensitivity. Selectivity can be achieved by use of mass spectrometry. Electron-impact (EI) or positive chemical ionization (CI) mass spectrometry can be selective, but these techniques lack sensitivity because of extensive ion fragmentation (6, 13). NICI mass spectrometry is both selective and sensitive, and selected ion monitoring (SIM) can further increase selectivity and sensitivity (2, 11, 16-18). An NICI SIM method was developed by Jansson and Wideqvist (12). This method used silica gel separation to eliminate interferences, and it used mirex as an internal standard. The ions monitored represented the different degrees of chlorination of chlordane and toxaphene and the (M - OC1)- fragments of PCB components. The latter resulted from oxygen leaking into the ion source. Our method differs; no preseparation column chromatography is needed, and a PCB that was not produced commercially is used as the internal standard. The need to monitor PCB interferences is eliminated by keeping the ion source free of oxygen. Our internal standard coelutes with toxaphene and, unlike mirex, is easily vaporized in the injection port and would not be found in environmental samples. In our method, the SIM ions are grouped into four retention time windows. Quantitation and confirmation ions are representive molecular ions and fragment ions of toxaphene components. Additional ions are monitored to account for interferences such as technical chlordane and to correct for 13Ccontributions from coeluting compounds.
0003-2700/87/0359-0913$01.50/0 0 1987 American Chemical Soclety
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ANALYTICAL CHEMISTRY, VOL. 59, NO. 6,MARCH 15, 1987
TECH. CHLORDANE 4
)
DDT
I
DIELDRIN
HEPTACHLOR
Retention time, rnin.
b
14
16
18
20
22
24
26
I 28
4
30
32
34
36
Figure 1. Gas chromatogram of toxaphene. ISTD = 2,2',3,4,4',5,6,6'-0ctachlorobiphenyl. Approximate retention times of interfering compounds are indicated. The spectrum of the peak marked with an asterisk is given in Figure 2.
EXPERIMENTAL SECTION Toxaphene and chlordane reference standards (technical grade) were obtained from the U.S. EPA a t Research Triangle Park, NC, and diluted with hexane to known concentrations. Quantitation was done relative to the internal standard 2,2',3,4,4',5,6,6'-octachlorobiphenyl (Ultra Scientific). This PCB congener is not present in commercial Aroclor mixtures, and thus, it is not found in environmental samples. Standards and samples were analyzed on a Hewlett-Packard 5985B GC-MS system equipped with a 30 m x 0.25 mm DB-5 fused silica capillary column (J&W Scientific) with helium as the carrier gas. The chromatographic tiwe-temperature conditions were as follows: splitless injection, 0.9 min; initial temperature, 80 "C, hold for 1 min; to 200 "C a t 10 deg/min; to 230 "C at 1.5 deg/min; to 280 "C at 10 deg/min. The injection port and transfer lines were maintained a t 285 and 280 "C, respectively. The flow of the methane reagent gas for chemical ionization, introduced through a modified transfer line (19),was regulated as needed to control the ion source pressure. The ion source temperatures for electron impact (EI),positive chemical ionization (CI), and NICI modes were 250, 250, and 100 "C, respectively. Ion source pressures in CI and NICI were 0.55 and 0.35 torr as measured by a capacitance monometer. The emission current was approximately 200 PA, and the electron energies were approximately 70 and 200 eV for E1 and CI/NICI, respectively. Fish were netted in Siskiwit Lake on Isle Royale in Lake Superior, frozen, returned to the laboratory, and ground in a meat grinder. The lake trout and whitefish samples were homogeneous composites of five to six fish of similar size and weight. Four carp were obtained from the mouth of the Saginaw River a t Lake Huron by electroshocking and composited in the same manner. Two composites of lake trout and whitefish, and one composite of carp were analyzed. Fish samples (approximately 12 g wet weight) were mixed with anhydrous Na2S04(1:6), spiked with the internal standard, and Soxhlet extracted with 1/1 hexaneacetone for 24 h. Lipids were removed by gel permeation chromatography (20). Extracts in hexane were passed over 1%
,
I
M/Z
Flgure 2. The EI, CI, and NICI spectra of an octachlorobornane. See peak marked with an asterisk in Figure 1.
deactivated silica gel and eluted with dichloromethane followed by methanol. The dichloromethane extracts were exchanged into hexane, reduced in volume to approximately 1 mL, and stored at -20 "C until analysis. Prior to GC-MS, extracts were reduced to approximately 200 pL under a gentle N2 stream.
RESULTS AND DISCUSSION EI, CI, and NICI Spectrometry of Toxaphene. Generally, the mass spectra of toxaphene under EI, CI, and NICI conditions in our laboratory agree with the findings of other investigators (10-13,18,21). The E1 spectra are characterized by abundant lower mass ions which are not structurally characteristic (as an example, see top spectrum of Figure 2 ) .
AtrlALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987
Table I. Ions Used for Selected Ion Monitoring of Five Chlorine Homologue Classes in Toxaphene Mixture ion cluster empirical formula mol w t
moni-
CTnHjnCln C;,H;;CI, CloH&17 C,,H,,CI, CiiHiCls' C;,H;oCi, CIoH7C1, C,nHoClo C;;H,Cl;, CloH&llo
M
342
340
1, 2
M - C1
343
341
1, 2, 3
M-C1
377
375
2, 3
M - C1
413
411
3, 4
M - C1
449
447
4
340 342 374 376 408 410 442 444 476 478
tored
quantita- confirmation ion tion ion
SIM window
The CI and NICI spectra are less complex and contain higher mass ions due to successive losses of C1 and HC1 from the molecular ion (see middle and bottom spectra of Figure 2). Molecular ions were not observed in the E1 and CI spectra, which is consistent with previous reports (10-13,18,21). In the NICI spectra, the most abundant ions were the M- for the hexachlorinated components and the (M - C1)- for the heptathrough decachlorinated compounds. It seems clear that NICI is an excellent ionization technique for the analysis of toxaphene. We found it to be approximately 100 times more sensitive than E1 or CI, and the presence of intense high mass ions makes NICI suitable for selective ion monitoring. The fragmentation of ions and the sensitivity of NICI are affected by the ion source pressure and temperature. Previous experiments in our laboratory have shown that maximum sensitivity for the analysis of a-chlordane, a structurally similar compound, was achieved a t a pressure of approximately 0.35 torr (22). Thus, our toxaphene studies were conducted at this pressure. The probability of dissociative electron capture increases with ion source temperature (23), thereby affecting the NICI sensitivity. Spectra of toxaphene recorded a t 100, 150, and 250 "C were compared. Generally, there was an increase in fragmentation with increasing ion source temperature. The intensity of the (M - 2C1)- and (M - 2C1- H)fragments increased relative to the (M - C1)- and molecular ions. To maximize the M- or (M - C1)- ions, an ion source temperature of 100 "C was used for the studies reported here. Selection of Quantitation Ions. The major components observed in toxaphene using NICI have 6 to 10 chlorine atoms. We monitor each of these homologue groups to provide accurate quantitation even in cases where environmental processes may have modified the original mixture's composition. As mentioned previously, the major ion cluster observed in the toxaphene NICI spectra is a t (M - C1)- except for the hexachlorinated compounds which generally give a strong Mcluster. Thus, ions are monitored from the M- cluster for the hexachlorinated bornanes and bornenes and from the (M C1)- cluster for the higher chlorinated components. The ions selected are common to both bornanes and bornenes so that quantitation includes both families of compounds. The specific ions chosen for monitoring are shown in Table I along with the empirical formula and molecular weight of the components being measured. The most abundant ions from a given isotopic cluster were generally selected to be the quantitation and confirmation ions. The SIM method was constructed so that only two or three homologue groups are being monitored at one time. The hexaand heptachlorinated components are monitored in the first retention time window, the hexa-, hepta-, and octachlorinated components in the second, the hepta-, octa-, and nonachlorinated components in the third, and the nona- and de-
915
cachlorinated components in the fourth. The window times are established by running a toxaphene standard and plotting the abundance of m / z 342, 343, 377, and 413. Window 1 begins at the first appearance of m / z 342 and ends at the first appearance of mlz 377. Window 2 begins at the end of window 1 and ends prior to the first major peak of m / z 413. Window 3 begins where window 2 ends and ends when m / z 377 is finished, and window 4 begins where window 3 ends and extends to the end of the GC program. Interferences. NICI is sensitive to other halogenated pesticides and organic compounds which coelute with toxaphene. While many of these compounds are not a problem when monitoring for selected ions, there are several compounds that give ions common to those of toxaphene. These include heptachlor, dieldrin, octachlorostyrene (OCS), endosulfan, diphenyl ethers, and technical chlordane which contains chlordane, nonachlor, and chlordene isomers as major components. In the method presented here, most of the interferences are eliminated by our choice of retention time windows. Heptachlor, OCS, endosulfan, and dieldrin all give ions that interfere with the toxaphene m / z 375, 377 ion clusters but elute during the first window where these ions are not being monitored. Unfortunately, this is not true for the major technical chlordane components. Chlordene isomers have a six-chlorine cluster at m/z 336 (M-) which interferes with the m/z 340 and 342 toxaphene quantitation ions. Chlordane isomers produce six-chlorine fragment clusters at m / z 336 (M - 2C1) and 338 (M - 2C1+ 2H) causing a similar interference. By monitoring mlz 336 and 338, we can calculate the relative contribution of chlordene and chlordane to the toxaphene quantitation using theoretical chlorine isotope ratios. The interfering area is then subtracted from the area of the quantitation ion. Similarly, interferences from chlordane compounds with the toxaphene quantitation ion 377 are corrected by monitoring m/z 371 and 373. Nonachlor isomers have a fragment cluster at m / z 332. The m / z 336 and 338 ions in this cluster can be mistaken for chlordene and chlordane ions in SIM. Corrections for these ions would be in error because the actual isotope ratios would be different than expected. Therefore, we monitor mlz 444 from the nonachlor molecular ion cluster to determine where the nonachlor compounds elute. These compounds are resolved from toxaphene in our GC program, and their interference is eliminated by omitting the areas of m / z 336 (one 37Cl)and 338 (two 37Cl)at these retention times from the toxaphene quantitation. Unfortunately, the NICI spectra of the chlorinated diphenyl ethers contain no distinguishing ions that can be used to monitor for their interference. An additional interference arises from compounds which give ions that are one mass unit lighter than those being monitored for toxaphene. If present in high abundance, the 13C contribution of these ions can significantly interfere with the toxaphene quantitation. This interference can be a result of fragmentation of toxaphene itself, for example, the overlap of (M - C1)- and (M - HCl)-. The 13C contribution can be determined and subtracted by monitoring the ion one mass lighter than the toxaphene quantitation ion. Final S I M Program. The SIM program in its final form is presented in Table 11. In addition to the quantitation and confirmation ions for each of the toxaphene homologues, ions are monitored to account for technical chlordane interferences, 13Cinterferences, and the internal standard (at mlz 428 and 430). The corrected area of each of the chlorine homologue classes is summed for a total toxaphene area, which is quantitated against the area of a toxaphene standard calculated in the same manner, all relative to the internal standard. An example calculation of an artificial mixture of toxaphene and technical chlordane is shown in Table 111. The areas of
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ANALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987 Log Meosured Conc..
Table 11. S I M Program Used for Quantitation of Toxaphene" window no. starting time of window, min stopping time of window, min
1 2 14.0 19.5
3 25.0
4 28.0
19.5 25.0
28.0
38.0
ions
336 338 340+ 341' 342* 343*
341+, 411' 411+, 447' 342, 412 412, 448 343*, 413* 413*, 449* 375+, 428" 376, 430'* 377*
336, 371 338, 373 340+, 375' 341+, 376 342*, 377* 343*.444
ng/g
S C
s
t t
9'
Includes ions necessary for correcting for interferences from coeluting chlorinated compounds. Key: +, confirmation ion; *, auantitation ion: i. internal standard.
each quantitation and correction ion were obtained by integrating the mass chromatograms in each of the four windows and summing. Corrections were calculated for the quantitation ions, and the total toxaphene area of the sample was given by the sum of the corrected quantitation ion areas. Corrections are based on the expected isotope ratios for a given number of chlorines or on the I3C contribution for 10 carbon compounds (11%). For example, the interference of m / z 336 to m / z 342 is calculated by subtracting the expected area of the A 6 ion in the six-chlorine cluster from the area of m / z 342. Likewise, the A + 4 interference of m / z 338 is subtracted from m / z 342. Note that the A + 2 contribution of m / z 336 to the area of m / z 338 is subtracted prior to this calculation, so that the interferences from 336 and 338 to 342 are figured independently. Evaluation and Application of SIM Program. We evaluated the NICI linear response by spiking toxaphene into fish tissue at concentrations of 0.01, 0.1, 1.0, 10, and 50 pg/g of whole fish. These values include the range of toxaphene concentrations found in most environmental samples. The fish was a white sucker from Siskiwit Lake, and it contained 0.014 pg/g toxaphene before spiking. This background level was subtracted from the spiking experiment results. Quantitation of spiked fish was done relative to a toxaphene standard concentration of 20 pg/mL. The measured and actual concentrations are compared in Figure 3, and these data indicate the response was linear for the concentration range tested. However, the slope was greater than 1 for total measured vs. actual toxaphene (solid line, Figure 3, y = 1 . 1 7 ~ - 0.64). At concentrations below the quantitation standard,
+
o " ' " ' " ' ~ ' ' ' ' " " ' " ~ ' ' ~ 0
1
2
4
3
Log Actual Conc..
5
ng/g
Figure 3. log measured concentration vs. actual concentration of toxaphene added to a fish matrix. Total toxaphene is shown by solid line, and quantitation based on a single peak is shown by dotted chain line. The dashed line shows y = x .
toxaphene measurements were lower than actual values, and at higher concentrations the reverse occurred. The ideal relationship (y = x) is shown by the dashed line. The instrument threshold may omit smaller peaks during integration, and this effect would be more pronounced a t low concentrations. To test this, we compared the actual and measured concentrations based on the integration of a single large peak that would be unaffected by threshold. This result is shown by the dotted chain line in Figure 3. The slope of this relationship (y = 1 . 0 6 ~- 0.27) is not significantly different than 1 (95% confidence limits). Thus,at low concentrations smaller peaks may be excluded during integration and measured concentrations may be underestimated. The detection limit was estimated to be 75 pg injected based on background noise and instrument response. This estimate is based on the overall toxaphene response and not on an individual peak within the mixture. Because of the potential for significant interference from technical chlordane in the quantitation of toxaphene, we tested the ability of our program to correctly distinguish toxaphene
Table 111. Example Quantitation Calculation of Toxaphene Using S I M Program quantitation ion m,'z area 342
275500
343 377
344200 367800
413 449 430
177730 8910 28315
correction ions mJ Z area 336 338 341 342 371 373 376 412 448
(A)
(Bj (C)
(D) (E) (F) (C) (H)
cn
8550 53300 175500 275500 1228 10970 87110 36450 5930
corrections
A
35/51a = 5870 X 100/51b)] X 81/51' = 58030 C X O . l l d = 19310 D X 0.11 = 30310 E X 53/44e = 1480 [F- ( E X 100/44f)] X 98/44' = 18220 G X 0.11 = 9580 H X 0.11 = 4010 I X 0.11 = 650 total toxaphene area = X
quantitation ion corrected area 192290
[ B - (A
313890 338520 173720 8260 1026680
ng of toxaphene = area X re1 rf X (ng istd, sample)/(area istd, sample) = (1026680) X (0.0121) X (107/28315) = 47 ng where re1 r@ = (ng toxaphene/area toxaphene) X (area istd/ng istd) from toxaphene standard "(A + 6)/A ratio for six-chlorine cluster. *(A + 2 ) / A ratio for six-chlorine cluster. c(A + 4)/A ratio for six-chlorine cluster. d13C contribution for 10 carbon atoms is 11%. '(A + 6)/A ratio for seven-chlorine cluster. '(A + 2)/A ratio for seven-chlorine cluster. g ( A + 4) /A ratio for seven-chlorine cluster. Relative resDonse factor.
ANALYTICAL CHEMISTRY, VOL. 59, NO. 6 , MARCH 15, 1987
Table IV. Quantitation of Toxaphene in Known Mixtures of Toxaphene and Technical Chlordane Using SIM Program
mixture
toxaphene concn, ppm
45 130 43
1 2
3
technical chlordane concn,
NI % recovery
ppm
response ratio
N
(std dev)
7.0 13 2.6
2:3 1:l 3:2
4 1 3
98 (15) 99 98 (16)
Table V. Toxaphene Concentrations (ng/g of Whole Fish) and Relative Distribution among Chlorine Homologue Classes in Fish Samples sample Siskiwit L a k e t r o u t Siskiwit whitefish Saginaw B a y carp toxaphene std"
toxaphene concn, n g / g
% distribution
6C1
7C1
8C1
9+1OC1
290
17
21 47
24 30 38 33
29
220 510
31 13 33
30 18 2 14
20
a Relative variation in t h e congener d i s t r i b u t i o n in toxaphene standards is *3%.
from technical chlordane. Three artificial mixtures of toxaphene and technical chlordane with known concentrations were prepared (see Table IV). Concentrations were selected such that their NICI response rations were approximately 23, 1:1,and 3:2 (at equal concentrations, the NICI response of chlordane is about 10 times that of toxaphene). These concentrations are representative of toxaphene to chlordane ratios of Great Lakes fish. Mixtures were then quantitated for toxaphene using a toxaphene standard containing no chlordane. Recoveries of toxaphene, shown in Table IV, averaged 98% with good reproducibility. The SIM program was also applied to the quantitation of toxaphene in fish composites from the Great Lakes region. Siskiwit Lake, located on Isle Royale in Lake Superior, is a remote, wilderness ecosystem receiving contaminants solely by atmospheric transport. In contrast, Saginaw Bay is a highly contaminated region because of its dense population and industrialization. Concentrations of chlorinated pesticides in fish differ by a factor of 100 between these two sites (24, 25). The toxaphene data are given in Table V. Siskiwit Lake trout and whitefish contain about 200-300 ng/g (whole fish) or about 0.2-0.3 ppm of toxaphene; the Saginaw Bay carp contain about 0.5 ppm. These toxaphene concentrations differ by less than a factor of 2 which is consistent with reports that toxaphene enters the Great Lakes region predominantly by atmospheric sources rather than from direct point sources (4, 7, 26). Thus, our quantitation method was successful a t measuring trace levels of toxaphene from a complex environmental matrix such as contaminated carp. One concern in the analysis of toxaphene is the degree of environmental transformation which changes the relative distribution of the toxaphene components due to physical or
917
biological processes (27). The relative distribution of toxaphene among the different chlorine homologue classes in the fish sampled is shown in Table V. By comparing the distribution with the toxaphene standard, we note that changes are not observed in the Siskiwit whitefish, but the toxaphene homologue distributions seen in the other fish samples are altered. Saginaw Bay carp were more altered than Siskiwit lake trout. These changes may be due to different metabolic processes or rates between species or to alterations that take place in the food chain prior to uptake by fish. Lake trout are higher in the aquatic food web than whitefish, while carp are a t the top of the benthic food web. Thus, toxaphene may show increased environmental transformations at higher levels in the food webs.
ACKNOWLEDGMENT We thank E. Stemmler for helpful discussions, B. McVeety for the Siskiwit fish samples, and D. Weidner for clerical assistance. LITERATURE CITED Parlar, H. Int. J . Environ. Anal. Chem. 1982, 2 0 . 141. Cairns, T.; Siegmund, E. G.; Froberg, J. E. Biomed. Mass. Spectrom. 1981, 8 , 569. Casida, J. E.; Holmstead, R. L.; Khalifa, S.; Knox, J. R.; Ohsawa, T.; Palmer, K. J.; Wong, R. Y. Science 1974, 783, 520. Rice, C. P.; Evans, M. S. Toxic Contaminants in the Great Lakes; Nriagu, J., Simmons, M. S., Eds.; Wiley: New York, 1984; Chapter 8. Hooper, N. K.; Ames, B. N.; Salch, M. A.; Casida, J. E. Science 1979, 205, 591. Jansson, B.; Vaz, R.; Blomkvlst, G.; Jensen, S.; Olsson, M. Chemosphere 1979, 4 , 181. Bidleman, T.; Olney, C. E. Nature (London) 1975, 2 5 7 , 475. Gooch, J. W.; Matsumara, F. J . Agric. Food Chem. 1985, 3 3 , 844. Jansson, B.; Wideqvist, U. Int. J . Environ. Anal. Chem. 1983, 73, 309. Holmstead, R. L.; Khalifa, S.; Casida, J. E. J . Agric. Food Chem. 1974. 2 2 . 939. Saleh, M.'A. J. Agric. Food Chem. 1983, 3 7 , 748. Jansson, B.; Widaqvist, U. Int. J . Environ. Anal. Chem. 1983, 73, 221. Ribick, M. A.; Dubay, G. R.; Petty, J. D.; Stalling, D. L.;Schmitt, C. J. Environ. Sci. Technol. 1982, 76, 310. Wideqvist, U.; Jansson, B.; Reutergardh, L.; Sundstrom, G. Chemosphere 1984. 13, 367. Bidleman, T. F.; Matthews, J. R.; Olney, C. E.; Rice, C. P. J . Assoc. Off. Anal. Chem. 1978, 6 7 , 820. Budde, W. L.; Eichelberger, J. W. J . Chromatogr. 1977, 734, 147. Wells, D. E.; Cowan, A. A. Anal. Proc. 1982, 79, 242. Thruston, A. D., Jr. EPA 600/4-76-010, 1976. Jensen, T. E.; Kaminsky, R.; McVeety, B. D.; Wozniak, T. J.; Hites, R. A. Anal. Chem. 1982, 5 4 , 2385. Stalling, D. L.; Tindle, R. C.; Johnson, J. L. J . Assoc. Off. Anal. Chem. 1972, 55,32. Stalling, D. L.: Huckins, J. N. EPA-600/3-76-076, 1976. Stemmler, E. A.; HBes, R. A. Anal. Chem. 1985, 5 7 , 684. Crow, F. W.; Bjorseth, A.; Knapp, K. T.; Bennett, R. Anal. Chem. IgSI. 53. 619. - Jaie, R.; Stemmler, E. A.; Eitzer, B. D.; Hites, R. A. J. Gr. Lakes Res. 1985. 7 7 . 156. ..., Swackhame;,-D. L.; Hites, R. A., Indiana University, Bloomington, IN, unoublished work. Rice, C. P.; Sampson, P. J.; Noguchi, G. E. Environ. Sci. Technol. 1986. 2 0 . 1109. Vaz, k.; Blomkvist, G. Chemosphere 1985, 14, 223
-. - - .
REXE~VED for review September 22,1986. Accepted November 19,1986. This work was supported by the US. Environmental Protection Agency, Grant No. 808865.
