2797
Anal. Chem. 1985, 57, 2797-2801
Determination of Atrazine, Lindane, Pentachlorophenol, and Diazinon in Water and Soil by Isotope Dilution Gas Chromatography/Mass Spectrometry Viorica Lopez-Avila,* Pat Hirata, Susan Kraska, Michael Flanagan, and John H. Taylor, Jr. Acurex Corporation, Energy a n d Environmental Division, 555 Clyde Avenue, Mountain View, California 94039
Stephen C. Hern Environmental Protection Agency, Environmental Monitoring Systems Laboratory, Las Vegas, Neuada 89114
Thls paper describes an isotope dllution GC/MS technlque for the analysis of low-parts-per-billlon concentratlons of atrazine, lindane, pentachlorophenol, and dlazinon In water and soil. Known amounts of stable-labeled Isotopes such as atrazlned,, Ilndane-d,, pentachlorophenol-"C and diazlnon-d ,o are spiked Into each sample prior to extraction. Water samples are extracted with methylene chloride; sol1 samples are extracted wlth acetone/hexane. Analysis Is performed by hlgh-resolutlonGWMS wlth the mass spectrometer operated In the selected ion monltoring mode. Accuracy greater than 86% and preclslon better than 8% were demonstrated by use of spiked samples. Thls technlque has been used successfully In the analysis of over 300 water and 300 sol1 samples. Detectlon limits of 0.1-1.0 ppb were achieved for the test compounds by selected Ion monltorlng GWMS.
Stable-isotope dilution analysis is an analytical technique in which a known quantity of a stable-labeled isotope is added to a sample prior to extraction, in order to quantitate a particular compound. The ratio of the naturally abundant and the stable-labeled isotope is a measure of the naturally abundant compound and can be determined only by gas chromatography/mass spectrometry (GC/MS) since the naturally abundant and the stable-labeled isotope cannot be completely separated gas chromatographically. Parameters such as quantitation ion(s) for isotope ratio measurements, spiking level of the stable-labeled isotope, and data processing have been reported to affect the accuracy and precision of the GC/MS determination ( I ) . Deuterated and 13C-labeledisotopes have been commonly used in environmental analysis (2-4). Although the availability of the stable-labeled isotopes is still a problem and the synthesis costs are quite high, the benefits from using stable-labeled isotopes in environmental analysis are quite remarkable. Similarity between the naturally abundant compound and the stable-labeled isotope can be used for two purposes: (a) to establish if the naturally abundant compound has degraded in the sample prior to analysis, this is the case when the stable-labeled isotope is added to the sample in the field immediately following sample collection (5-7); and (b) to provide a continuous quality control, this is the case when the stable-labeled isotope is added to the sample in the laboratory immediately prior to sample extraction (2). The quantitation technique involving isotope dilution requires that the stable-labeled isotope be recovered, regardless of the value of recovery (2). Thus, method accuracy and precision should not be affected by the sample matrix. This paper describes an isotope dilution GC/MS technique for the analysis of low-parts-per-billion concentrations of atrazine, lindane, pentachlorophenol, and diazinon in water 0003-2700/85/0357-2797$01.50/0
Table I. SIM Descriptors Used in GC/MS Analysis begin mass
end mass
dwell time, s set actual
Descriptor I" 178.5 180.5 187.5 199.5 204.5 223.5 265.5 271.5 303.5 313.5
179.5 181.5 188.5 200.5 205.5 224.6 266.5 272.5 304.5 314.5
0.050 0.050 0.050 0.050 0.050 0.050 0.050 0.050 0.100 0.100
0.052 0.052 0.053 0.052 0.053 0.053 0.052 0.052 0.105 0.106
0.050 0.120 0.120
0.052 0.105 0.105
Descriptor IIb 181.5 265.5 271.5
188.5 266.5 272.5
" Total acquisition time, 0.633 s; total scan time, 0.690 s; centroid sampling intensity, 0.100 ms. bTotal acquisition time, 0.262 s; total scan time, 0.300 s; centroid sampling intensity, 0.200 ms. and soil. Stable-labeled isotopes, such as atrazine-d6, lindane-d6, p e n t a c h l ~ r o p h e n o l - ~and ~ c ~diazinon-dlo, , are spiked into each sample prior to extraction, and the ratio of the naturally abundant compound and the stable-labeled isotope is determined by high-resolution GC/MS with the mass spectrometer operated in selected ion monitoring (SIM) mode.
EXPERIMENTAL SECTION Apparatus. A Finnigan 4021 quadrupole mass spectrometer coupled to a 9610 gas chromatograph and an Incos 2300 data system was used for all measurementsreported here. Calibration standards and sample extracts were injected automatically by a Varian autosampler. Compound separations were performed on a fused silica capillary column 30 m X 0.25 mm i.d. (DB-5, 0.25 Fm film thickness, J&W Scientific, Rancho Cordova, CA) at the following conditions: splitless injection at 50 "C followed by temperature programming to 300 "C at 15 "C/min; injector temperature of 260 "c;transfer line temperature of 280 "C; carrier gas (He) at 10 psi pressure. The mass spectrometer operating conditions were ion source temperature at 300 "C, electron energy of 70 eV, and selected ion monitoring mode for ions at m / z 188, 200, 205, 181, 224, 304, 314, 266, and 272. TWOSIM descriptors have been used for GC/MS analysis (Table I). Descriptor 1was used in the analysis of water samples for all four compounds and in the analysis of soil samples for atrazine, lindane, and diazinon. Descriptor 2 was used in the analysis of soil samples for pentachlorophenol, The total acquisition times, total scan times, and the dwell times for the various ions monitored are given in Table I. Reagents and Standard Compounds. Analytical reference standards of atrazine, lindane, pentachlorophenol, and diazinon 0 1985 American Chemical Society
2798
ANALYTICAL CHEMISTRY, VOL. 57, NO. 14, DECEMBER 1985
were obtained from the U.S. EPA Pesticides and Industrial Chemicals Repository (MD-8),Research Triangle Park, NC. Stock solutions were prepared in pesticide grade methanol (Baker resi-analyzed) and stored a t -10 OC. Stable-labeled isotopes (atrazine-d,, lindane-d,, and diazinon-dlo) were synthesized by Pathfinder Laboratories, St. Louis, MO. Pentachl~rophenol-~~C, was obtained from MSD-Isotopes, Division of Merck Frosst Canada, Inc., Montreal, Canada. Chemical purity of the stable-labeled isotopes was determined by gas chromatography with flame ionization detection using concentrated stock solutions (concentration 10 mg/mL). Isotopic purity determinations were performed by GC/MS and directprobe MS. Approximately 100 mg each, accurately weighed, of atrazine, lindane, pentachlorophenol, and diazinon and their corresponding stable-labeled isotopes, were dissolved in 10 mL of methanol to provide stock standards. These solutions were stored at -10 "C in a freezer. Two composite standards of the four unlabeled compounds and the four stable-labeled isotopes were prepared from these individual stock solutions at a final concentration of 100 pg/mL in methylene chloride. These standards were prepared fresh monthly. Working calibration standards were prepared by serial dilution of the composite standards with methylene chloride, at five concentrations, 0.1, 1.0, 2.0, 5.0, and 10 pg/mL, for the unlabeled compounds, and 1pg/mL for the stable-labeled isotopes. Water Extraction. Standard water samples were prepared by spiking concentrated solutions of atrazine, lindane, pentachlorophenol, and diazinon into organics-free water (pH 6.7) at various concentrations. Stable-labeled isotopes were added at 4 ppb or 80 ppb each. The standard water samples and real samples (1 L) were extracted vigorously, for 2 min, in a 2-L separatory funnel with 200 mL of methylene chloride. Extraction was performed three consecutive times, each time using fresh aliquots of methylene chloride. The extracts were combined, dried through a column of anhydrous sodium sulfate, and concentrated to 4 to 6 mL in a Kuderna-Danish evaporator. Further concentration to 1 mL was performed using nitrogen blowdown evaporation. Soil Extraction. Standard soil samples were prepared as follows: 50-g aliquots of the fresh sandy loam soil were slurried with 10 mL of organics-free water and were spiked with various amounts of atrazine, lindane, pentachlorophenol, and diazinon. The spike was added in 1OO-wL of methanol to the wet soil and was allowed to equilibrate with the soil for 1 h. Stable-labeled isotopes were added at 4 ppb each and were also allowed to equilibrate with the soil for 1 h. Following equilibration, the soil slurry was extracted as shown in Figure 1. Two separate aliquots were extracted for each sample: one aliquot was extracted at neutral pH to separate atrazine, lindane, and diazinon; the other aliquot was extracted at acidic pH to separate pentachlorophenol. The aliquot designated for extraction at neutral pH was extracted three times, with 100 mL of acetone/hexane (50/50). An ultrasonic cell disruptor, in pulsed mode at 50% duty cycle, was employed to enhance the contact between the extraction solvents and soil. Following each extraction, the soil was allowed to settle, the solvent was decanted, and the combined supernatants were dried through a column of anhydrous sodium sulfate (5-cm bed height; 3-cm diameter). Concentration of the extract was performed with a KudernaDanish evaporator. Final volume was adjusted to 1 mL by use of nitrogen blowdown evaporation. The extraction at acidic pH was performed as follows: 50-g aliquots of the soil sample were slurried with 10 mL of organics-free water and were spiked with the stable-labeled isotopes. Following equilibration, the soil slurry was adjusted to pH 51 with approximately 10 mL of H2S04(1+ 1)and was extracted with 100 mL of acetone/hexane (50/50) using an ultrasonic cell disruptor. The extraction with acetone/hexane (50/50) was repeated two additional times. Each time the sonicator probe was activated for 3 min. Following each extraction, the soil was allowed to settle, the solvent was decanted, and the combined supernatants were filtered through a column of Celite (5-cm bed height; 1.5-cm diameter). The filtrates from the Celite column were combined. To remove water, the combined filtrates were transferred to a separatory funnel and washed twice with 100 mL of acidified organics-free water. The layers were separated. The organic layer
I
I ' Weigh aliquot lor extraction at pH 51
Weigh aliquot for extraction at neutral PH
dlazinon.dl0 equlltbrate lor 1 h i
equilibratelor 1 hr I
L
Acidify to pH I 1 sonicate 3X with acetonelhexane
Sonicate 3 X with acetonelhexane
Decant extract dry through Na2S04 concentrate
I-
Decant Solvent, filter
Spike Phenanthrenedlo
i----L----l
I
GCiMS atrazine, lindane. diemon
I
I
Extract Z X with 100 mL acidified water
t
t
t Aqueous layer
Hexane layer
.(. Extract 3 X with methylene chloride
I V Composite concentrate
Methylene chloride
t Discard aqueous
I
I
GCiMS pentachlorophenol
I
Flgure 1. Extraction of atrazlne, lindane, pentachlorophenol, and dlazlnon from soil.
contained pentachlorophenol; the aqueous layer contained traces of pentachlorophenol. To recover these traces, the aqueous layer was extracted three times with 50 mL of methylene chloride. After the last extraction the aqueous layer was discarded. The methylene chloride was combined with the acetone/hexane extract and was concentrated to approximately 4 mL on a Kuderna-Danish evaporator. Further concentration to 0.5 mL was performed with a slow stream of nitrogen. Acetone was then added to adjust the volume of the extract to 4 mL from which an aliquot of 1mL was taken for GC/MS analysis. Quantitation. After a preliminary ratio measurement using a five-point calibration, two calibration standards were subsequently chosen for daily calibration: one whose concentration of atrazine, lindane, pentachlorophenol, and diazinon was at 0.1 pg/mL and the other at 1 pg/mL. All calibration standards contained the stable-labeled isotopes and phenanthrene-dlo at 1 pg/mL. Whenever sample concentration exceeded 1 pg/mL, additional calibration standards at 10 pg/mL were analyzed with the samples. The calibration standards were analyzed at the beginning of the day and after the last sample during a 10- to 12-h period. The concentration of atrazine, lindane, pentachlorophenol, and diazinon was calculated from
e=---A Aisotope
WiIVisotope
1
RR
Wsample
(1)
where C is the concentration of test compound in parts per billion if W is in liters for water samples and in kilograms for soil samples, A is the area of the quantitation ion of the test compound, AIsotope is the area of the quantitation ion of the stable-labeled isotope,
ANALYTICAL CHEMISTRY, VOL. 57, NO. 14, DECEMBER 1985
2799
Table TI. Mass Spectra, Ions Selected for Quantitation by SIM GC/MS Technique, and Relative Responses ion selected for no. of quantitation relative determi(m/z) responsea*b nations mass spectrum m / z (intensity) compound atrazine atrazine-d, lindane lindane-d6 pentachlorophenol pentachlorophenol-13C6 diazinon
200 (IOO), 215 (60), 58 (541, 93 (37), 202 (331, 217 (211, 68 (361, 69 (23)205 (loo), 58 (77), 220 (61), 69 (461, 94 (391, 178 (391, 143 (201, 222 (20) 181 (loo), 183 (95), 217 (65), 219 (79), 109 (881, 111 (811, 51 (70), 220 (39) 224 (loo), 222 (85), 112 (521, 185 (53), 187 (5% 114 (33), 226 (47), 54 (35) 266 (loo), 268 (66), 264 (621, 165 (26), 167 (26), 270 (23), 202 (16)
200 205 181 224 266
0.993 f 0.058 0.184 f 0.025 1.134 f 0037 0.096 k 0.003 1.117 f 0.169
15 15 12 17 16
272 (loo), 274 (66), 270 (62), 170 (27), 172 (26), 205 (131, 207 (171
272
0.106 f 0.01
16
179 (loo), 137 (94), 304 (661, 152 (71), 199 (53), 93 (50), 66 (371, 97 (34)
304
15
diazinon-d,,
138 (loo), 183 (99), 153 (76), 99 (52), 200 (401, 93 (451, 314
314
1.299 f 0.228 1.402 f 0.071 0.034 f 0.007
67 (49), 66 (49)
12
15
"Relative responses were determined using standards at 0.1; 1.0; 2.0; 5.0; 10.0 pg/mL each standard being analyzed in triplicate. Phenanthrene-d,, was spiked at 1.0 pg/mL. *Relative responses of stable-labeled isotopes have been determined relative to phenanthrene-dlo.
Wisotopeis the amount in micrograms of the stable-labeledisotope that was spiked into the sample prior to extraction, RR is the relative response of the test compound to the corresponding stable-labeled isotope, and W,,ple is the volume of water sample (liters) or weight of soil sample (kilograms). In the case of pentachlor~phenol-~~C~, Aisotopeis the adjusted area of ion at mlz 272 (eq 2); this is necessary due to 3.4% contribution of the ion at mlz 266. Apentachlorophenol-'3Cg
=
- A266
0.034
SIM DESCRIFTOR 1
SIM DESCRIPTOR 1 m / r 188
loo0
1t 1
.*
I -
979 1213164 1064840
2.6
1
(2)
m/z 188
1
1
i I I
948 10648. 21558. 1
1064640
p =5
7584. 13966.
L
RESULTS AND DISCUSSION Chromatography. Chromatographic separation of atrazine, lindane, diazinon, pentachlorophenol, atrazine-d5, lindane-d6, diazinon-dlo, penta~hlorophenol-~~C6, and phenanthrene-dlo (internal standard) is presented in Figure 2. Each unlabeled compound in Figure 2 was present a t a concentration of 0.1-1.0 pg/mL, while the stable-labeled isotopes were present a t 1 Kg/mL (sample size 1 pL). In 15 repetitive injections of the calibration standards the maximum deviation from the average retention time for any compound was less than 5 s. The chromatograms in Figure 2 show that the stable-labeled isotope coelutes with the unlabeled compound as is the case of pentachlorophenol (Figure 2c) or it is only slightly resolved as in the case of atrazine, lindane (Figure 2a,b), and diazinon (Figure 2d). In the later case, the stable-labeled isotope eluted from the chromatographic column 3-5 s before the naturally abundant compounds. Total analysis time was 20 min; in addition a 10-min cooling cycle between runs was allowed. The analysis time could be shortened by 10 min since the temperature a t which the compounds elute from the fused silica capillary is approximately 235 OC. This is not practical however, since less volatile materials in the sample extract that tend to deposit either in the injector or onto the front-end of the capillary column could cause peak tailing, especially for pentachlorophenol and atrazine. If poor peak shape or sensitivity problems are experienced, replacement of the injection port liner and clipping off approximately 30 cm from the front end of the fused silica capillary column are recommended. Quantitation. The abundances of eight major fragment ions in the mass spectra of atrazine, lindane, pentachlorophenol, diazinon, and their stable-labeled isotopes are summarized in Table 11. In selection of the quantitation ions for the SIM technique, consideration was given primarily to the most intense ions in the mass spectra to maximize the instrument response. For three of the compounds it was possible to select the base peaks for quantitation. In the case of diazinon and diazinon-dlo this was not possible because of overlap of several fragment ions. To avoid this, the molecular
n
1.61
I
I
137886
900 1021
scan Time
950 10 55
900 10 21
1
2531 908268 ,148?10 n i
1
TlIllE
SIM DESCRIPTOR 1
SIM DESCRIPTOR 2
1
100.0
Scan
950 10 55
413184 1000
10646110.
L
I(
c
I I
m/z 304
,
I
981
24672 46964.
2400 1200
2450 1215
2500 1230
Scan Tlme
900 10 21
950 10 55
n T
Flgure 2. Selected ion monitoring chromatograms for: (a) atrazine (mlz 200), atrazine-d, ( m l z 205), phenanthrene-d,, ( m l z 188); (b) lindane (mlz 181), lindane-d, ( m l z 224), phenanthrene-d,, (mlz 188); (c) pentachlorophenol (m l z 266), pentachlorophen~I-'~C, (m / z 272). phenanthrene-d,, ( m l z 188); (d) diazinon (mlz 304), diazinon-d,, ( m l z 314), phenanthrene-d,, ( m l z 188).
ions a t m / z 304 and 314 were selected for quantitation. Under ideal conditions the relative responses on each of the four naturally abundant compounds relative to their corresponding stable-labeled isotopes would be 1.00. This is not always the case, since errors introduced in the preparation of standards and in the GC/MS analysis could lead to relative standard deviations as high as 15%; thus, the relative responses need to be determined by using standards of known concentration. Relative responses of the stable-labeled isotopes were determined by using phenanthrene-dloas internal standard. They are used in the quantitation of the stablelabeled isotopes and their values give an indication of the instrument detection limit. For example lindane-d, and pentachl~rophenol-~~C, give almost identical responses while atrazine-d5response is twice that of lindane-& Consequently,
ANALYTICAL CHEMISTRY, VOL. 57, NO. 14, DECEMBER 1985
2800
Table 111. Accuracy and Precision Data for Atrazine, Diazinon, Pentachlorophenol, and Lindane by Isotope-Dilution GC/MS
spike level, ppb 1
matrix
parameterb
water
A f SD RSD n A f SD RSD n A f SD RSD n A f SD RSD n A f SD RSD n A f SD RSD n A f SD .RSD n A f SD RSD n A f SD RSD n A f SD RSD n
5
water
10
water
50
water
20
soil
40
soil
100
soil
200
soil
1000
soil
10000
soil
atrazine
lindane
95.2 f 5.5
98.6 f 7.9
5.8
8.0
3 93.5 f 4.2 4.4 3 97.2 f 2.3 2.4 3 86.0 f 11.3 13 3 115.3 f 4.7 4.1 3 93.2 f 5.4 5.8 4
3 89.1 f 3.0 3.4 3 89.0 f 2.6 2.9 3 114.3 f 12.9 3 109.0 f 5.6 5.1 3 90.2 f 3.3 3.7 4
a
a
103.3 f 4.9 4.8 3
109.3 f 1.2 3
a
a
a
a
11
pentachlorophenol 100.4 i 5.9 6.0 6 109.8 f 15.9 14 5
107.6 f 7.7 7.2 3 93.5 f 0.5 0.5 3
diazinon
89.4 f 3.9 4.4 3
105.3 f 4.7 4.5 3 103.6 f 2.9 2.6 3 a
102.7 f 15.6
a
15
94 f 7.9 8.4 4 117.6 f 8.1 6.9 3 a
1.1
100.7 f 3.5 3.5 3 89.7 f 1.5 1.7 3
3 92.8 f 5.3 5.7 4 a
100.0 f 4.0 4.0 3 a a
'Accuracy and precision data not available at this concentration. b A f SD, accuracy (average recovery f standard deviation); RSD, relative standard deviation (percent); n, number of determinations Table IV. Accuracy and Precision Data for the Stable-Labeled Isotopes by GC/MS
spike level, ppb 4
A
,
matrix
parametera
atrazine-d,
lindane-d6
water
& SD RSD n A f SD RSD n A f SD RSD n A f SD RSD n
87.0 f 14.7
98.2 f 15.2 15 196 73.5 f 12.1 16 84 93.5 f 22.9 24 28 82.5 f 19 23 57
80
water
80
soil
4
soil
f
A
17
195 78.5 f 18.6 24 82
87.9 f 22.9 26 28 77.9 f 20 26 57
pentachl~rophenol-~~C~ diazinon-dIo 80.3 f 19.1 24 197 64.6 f 22.6 35 64 65.0 f 21.1 32 25 80.7 f 20 25 57
96.9 & 1.55 16 196 82.9 f 20.7 25 79 85.8 22.5 26 28 82.8 f 20 24 57
SD, accuracy (average recovery f standard deviation); RSD, relative standard deviation (percent); n, number of determinations.
the instrument detection limit for atrazine and atrazine& is lower by approximately a factor of 2 compared to lindane and pentachlorophenol. Likewise, since the relative response of diazinon-dlo is three times lower than that of lindane-& the instrument detection limit for diazinon and diazinon-dlo is three to four times higher than for lindane. Typical instrument detection limits at signal/noise ratio of 10 and with the instrument operated in the SIM mode are in the range of 10-50 pg for lindane and atrazine, 50-100 pg for pentachlorophenol, and 100-200 pg for diazinon. Method Accuracy and Precision. Twelve to 17 standard water samples and 10 to 13 standard soil samples containing the four compounds were analyzed by the isotope dilution GC/MS procedure. Compound concentrations ranged from 1 to 50 ppb for water samples and 20 to 10000 ppb for soil samples. The accuracy and precision data are presented in Table 111. These results indicate that the method accuracy (average recovery) is greater than 86%, and method precision given as relative standard deviation (RSD) is better than 8%. Twenty out of 28 of the RSD values were equal to or less than
8% and only 3 out of 28 were greater than 8% but below 15%. Since in the isotope dilution GC/MS procedure quantitation is done from the ratio of response of the naturally abundant compound to the stable-labeled isotope, the absolute recovery of the stable-labeled isotope is not critical. Typical recoveries using real samples spiked with stable-labeled isotopes, at 4 and 80 ppb, are presented in Table IV. Results obtained on a set of almost 200 water samples spiked with the stable-labeled isotopes a t 4 ppb indicated average recoveries greater than 80% with RSD values between 15 and 25%. Results obtained on soil samples indicate slightly larger RSD's (23-32%). The precision data for the naturally abundant compounds is better than 8% for at least 80% of the measurements; thus it can be concluded that method precision of the isotope dilution GC/MS technique is improved by a factor of 2 to 3 over the method precision of the standard GC/MS technique, which uses internal standard calibration. Although superior in terms of accuracy, precision, and sensitivity, the SIM GC/MS technique developed here lacks specificity when compared to the standard GC/MS technique
2801
Anal. Chem. 1985, 57,2801-2806
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
