Anal. Chem. 1990, 62,1867-1871
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Simultaneous Dual-Column, Dual-Detector Gas Chromatographic Determination of Chlorinated Pesticides and Polychlorinated Biphenyls in Environmental Samples Gregory S. Durell*J and Theodor C. Sauer2 Battelle Ocean Sciences, 397 Washington Street, Duxbury, Massachusetts 02332, and Marine Sciences Unit, Arthur D . Little, Inc., Acorn Park, Cambridge, Massachusetts 02140
The lack of confirmation of ldentlfled analytes In envlronmental gas chromatography (GC) that uses the tradltlonal onecolumn, onedetector systems (e.g., GGelectron capture detectlon with a nonpolar column) often ralses questions as to the valldlty of the data. To avold mlsldentiflcatlon of chlorinated pestlcldes and polychlorlnated blphenyls (PCB), we conducted slmultaneous dual-column, dualdetector GC analysls. WltMn one GC Instrument, InJectedsample extracts were spilt In two and each portlon passed through a caplllary column of different polarlty. A tradltlonal nonpolar column, 085, was connected to an electron capture detector for lnltlal Identiflcatlon of analytes; a more polar column, DB-17, was used wlth the halogen-speclflc electrolytlc conductlvlty detector for conflrmatlon analysls. GC column retention characteristlcs were determined for a large set of environmentally Important pesticides and PCB congeners for the DB-5 and DB-17 analytlcal columns. The dual-column, dual-detector system was then evaluated on a large number of envlronmental samples of dlfferent matrix types. Results lndlcated that a substantial number of analytes, especially pesticides, may be Incorrectly Identifled In envlronmental samples wlth onetolumn, one-detector systems. Use of a slmultaneous dual-column, dual-detector system, substantially decreases the risk of false-posltlve ldentlflcatlons without slgniflcantly lncreaslng the cost or tlme of analysls.
INTRODUCTION High-resolution capillary gas chromatography with 63Nielectron capture detection (GC-ECD) analysis is one of the most useful analytical techniques for the analysis of polychlorinated biphenyls (PCBs) and chlorinated pesticides in environmental samples (1-4). The GC-ECD and other detector (e.g., chromatography with electrolytic conductivity detection (GC-ELCD)) are especially useful alternatives to t h e preferred gas chromatography/mass spectrometry (GC/MS) when analyte concentrations are below the detection limits of GC/MS. The major drawback to these non-GC/MS single-column, single-detector systems is their inability to positively identify analytes in samples. This often raises serious questions about the validity of the data reported (5). Because of the compound complexity in some sample matrices, the possibility of false positive identifications from interfering unknown compounds becomes significant. To reduce the incidence of false positive identifications and improve the quality of the data, initial GC identifications must be confirmed. Additional analysis time and cost have deterred many analytical laboratories from conducting confirmatory analysis even though this analysis is recommended (6). An Battelle Ocean Sciences. *Arthur D. Little, Inc.
alternative to analyte confirmation by GC/MS is to perform both the initial identification and subsequent confirmation using a GC with a nonspecific or semispecific detector, fitted with two columns of different retention characteristics. To streamline initial and confirmatory analyses, a dualcolumn, dual-detector GC system was developed to simultaneously identify and c o n f i i analytes in sample extracts. This system is different than the simultaneous dual-column, single-detector systems that have previously been documented (7). An injected sample extract was split between two capillary columns of different polarities (a nonpolar column, DB-5, and a more polar column, DB-17) which were connected to two detectors of slightly different specificity to chlorinated compounds. The two detectors were the 63Ni-electron capture detector (ECD) and the electrolytic conductivity detector (ELCD). The ELCD is a halogen-compound-specific detector that does not response to some nonhalogenated compounds which the ECD recognizes (8). Thus, many of the interfering compounds typically detected by GC-ECD in organically complex samples are not detected by GC-ELCD. With this dual-column, dual-detector method, identification and confirmation of analytes were obtained in one GC run. GC conditions were optimized for simultaneous separation and identification of 34 environmentally important chlorinated analytes. The DB-5 and DB-17 column separation information for the selected pesticides and PCB congeners is presented in this work. The dual-column, dual-detector method was evaluated with many environmental samples of different sample matrices. The samples were analyzed for 15 selected chlorinated pesticides and 19 major PCB congeners. The usefulness of this method was established by comparing the number of confirmed identifications to the number of unconfirmed retention time matches that could have been misidentified by use of a one-column, one-detector method. In addition to demonstrating the results of the dual-column, dual-detector analysis, this paper presents the advantages of using two different detector systems, evaluates the method on different environmental matrices, and provides evidence for performing confirmation analysis.
EXPERIMENTAL SECTION GC Configuration. A Hewlett-Packard 5890A gas chromatograph equipped with a 63Nielectron capture detector, a Model 4420 electrolytic conductivity detector (0.1.Corp., College Station, TX), and a split/splitless inlet employed in the splitless mode was modified to include two capillary columns, a DB-5 column and a DB-17 column (J&W Scientific, Folsom, CA). The nonpolar DB-5 column was connected to the ECD (DB-5/ECD) and the more polar DB-17 was coupled with the ELCD (DB-17IELCD). The DB-5 and DB-17 columns are both fused silica columns; the DB-5 column has a stationary phase of 95% methylsiliconeand 5% phenylsilicone, and the DB-17 column has a stationary phase of 50% methylsilicone and 50% phenylsilicone. Both columns were 30 m long and had a 0.25 mm i.d. and a 0.25-pm stationary
0003-2700/90/0382-1867$02.50/00 1990 American Chemical Society
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phase film thickness. Hydrogen was used as the carrier gas at a flow rate of approximately 1.5 mL/min. Hydrogen was also used as the make-up gas for the ELCD. The make-up gas for the ECD was 95% argon/5% methane at a flow rate of 30 mL/min. Injector and detector temperatures were 290 and 300 "C, respectively. The ELCD was set in the halogen mode with a reactor tube temperature of 900 OC. 1-Propanol was used as the ELCD electrolyte solvent. To split the injected sample between the two columns, several options, including Y-tubes and two-holed ferrules (7), were considered. The arrangement that was chosen consisted of simply inserting both columns side by side through the injection port nut and soft graphite ferrule (which had been slightly enlarged) into the injection port liner, just as would be done for a single column. Care was taken in tightening the nut a t the injection port so as to not twist the columns around each other and cause them to break. An internal standard was used for analyte quantification, making it unnecessary to know the exact sample volume diverted to each column. Three microliters of sample extracts was injected by an H P 7673A autosampler. Data acquisition and reduction were accomplished through both an HP3393A integrator, which gave real-time hardcopy chromatograms of either detector signal, and an HP A Series minicomputer operating with PeakPro chromatography software (Beckman, Inc., Waldwick, NJ) for subsequent data manipulation of both detector signals. Analyte Selection and GC Separation, For preparation of GC calibration standard two National Institute of Standards and Technology (NIST) standard solutions, one of the pesticides and the other of the PCB congeners, were combined with tetrachloro-rn-xylene (TCMX). TCMX and decachlorobiphenyl (Cllo(209)),which was in the PBC mixture, were used as internal standards and relative retention index (RRI) reference compounds. The RRIs of TCMX and Cllo(209)were designated as 0 and 100, respectively. The 34 chlorinated pesticides and PCB congeners chosen for this study are presented in Table I. The PCB congeners were labeled according to their level of chlorination and B.Z. (Ballschmiter & Zell) number (e.g., C1, (8)).The selected PCB congeners represent the dominate PCB congeners of the major environmentally important Aroclors, which include the less chlorinated Aroclors, 1016, 1232, and 1242 through Aroclors 1248 and 1254 to the highly chlorinated Aroclors 1260 and 1262. Our work has shown that these PCB congeners are not only important for PCB/Aroclor identification but represent total PCB/ Aroclor concentrations well and are also useful for accurate quantification of total PCB concentrations at any level of chlorination (9-11). Although the use of these individual congeners significantly reduce the amount of time required for quantification, it does not replace qualitative identification of Aroclor patterns for confirmation purposes. Since both the DB-5 and DB-17 columns were operated simultaneously, it was necessary to develop a GC temperature program that would best resolve the analytes on both columns. A number of temperature programs were evaluated and the following program was selected as most appropriate: a 1-min hold a t 50 "C, 50 to 150 "C a t 4 OC/min, 150 to 280 OC a t 2 OC/min, and a 5-min hold at 280 "C. Because the DB-5 column is the more commonly used of the two column types, it was designated as the primary column on which separation of all analytes was to be achieved. Analyte separation on the confirmatory column was to be as complete as possible. The temperature program used gave optimum separation on the DB-5 column, and near optimum separation was achieved for the DB-17 column. All analytes in Table I are resolved on the DB-5 column. However, there are two or three instances of coelution of analytes on the DB-17 column: for lindane and C13 (18), o,p'-DDD and C15 (118), and p,p'-DDT and Cls (126). Dieldrin and p,p'-DDE sometimes also coelute on the DB-17 column. Therefore, in instances where both of these analyte pairs are present, confirmation may not be established. With some other temperature programs, slightly better separations on the DB-17 column were achieved for this complex analyte mixture but resulted in worse separation on the DB-5 column. However, the complex analyte mixture did not allow for perfect separation on the DB-17 column under any of the GC conditions evaluated. The GC conditions used in this work are
Table I. Elution Order, Retention Time (RT), and Relative Retention Index (RRI) for Chlorinated Pesticides and PCBs on DC-5 and DB-17 Chromatographic Columns" DB-5
analyte TCMX Clz (8) HCB lindane c13 (18) c13 (28)
heptachlor C11 (52) aldrin
c1, (44)
heptachlor epoxide C1, (66) o,p'-DDE C15 (101) a-chlordane trans-nonachlor dieldrin p,p'-DDE c4
(77)
o,p'-DDD C16 (118) p,p'-DDD O,P '-DDT Cl, (153) C15 (105) p,p'-DDT Cl, (138) C15 (126) C17 (187) C1, (128) C17 (180) mirex C17 (170) C1, (195) C1, (206) '2110 (209)
elution order 1 2 3 4 5 6 7 8
DB-17
RTb RRI
e1ution order
RRI 0.00 11.09 7.97 18.19 18.19 24.32 23.18 30.07 28.38 35.39 38.69 40.90 45.85 43.69 44.49 42.18
10 11
26.11 28.79 28.99 30.89 31.67 35.01 35.82 37.77 38.34 39.33 41.75
5.62 6.04 10.03 11.66 18.67 20.37 24.46 25.66 27.73 32.81
8 10 11
30.03 36.07 34.37 39.94 39.94 43.28 42.66 46.41 45.49 49.31 51.11
12 13 14 15 16
42.80 44.67 44.88 45.01 45.44
35.01 38.93 39.37 39.65 40.55
12 16 14 15 13
52.31 55.01 53.83 54.27 53.01
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
46.80 43.40 47.47 44.81 47.80 45.50 48.08 46.09 50.12 50.37 51.03 52.28 51.12 52.46 52.14 54.60 52.31 54.96 54.17 58.86 54.43 59.41 55.12 60.86 55.92 62.53 56.69 64.15 60.33 71.79 61.31 73.84 62.75 76.86 66.41 84.54 71.31 94.82 73.78 100.00
17 18 19 20121 20121 24 23 22 25 27/28 26 27/28 29 30 31 32 33 34 35 36
57.16 49.80 57.39 50.22 58.15 51.62 59.74 54.53 59.74 54.53 62.70 59.97 62.44 59.49 61.21 57.23 63.60 61.62 65.34 64.81 65.13 64.43 65.34 64.81 65.52 65.14 69.00 71.53 70.18 73.70 72.62 78.18 74.30 81.26 78.19 88.40 81.80 95.03 84.51 100.00
9
0.00
1 3 2 415 415 7 6
RTb
9
a The PCB congeners are identified by level of chlorination and the specific congener B.Z. number (e.g., Clz (8) = dichlorobiphenyl (8)). *Retention times are given in minutes.
suitable for simultaneous dual-column analysis as long as the DB-5 column is the primary column and the DB-17 is the confirmatory column. Instrument detection limits (IDLs) were determined for all analytes on each detector (Table 11). The EPA-suggested method in calculating IDLs used in our study involved analyzing the low concentration standard mixture (20 pg/fiL of each analyte) 5 times, determining the standard deviation for each analyte from the five runs, and then multiplying the standard deviation by 3. Method Evaluation. To evaluate the dual-column, dualdetector system, samples of different environmental matrices collected during a survey in the Atlantic Ocean, 250-km off the coast of Florida, were analyzed for the selected pesticides and PCB congeners (12,13).The environmental samples included seawater filter and filtrate, microlayer filter and filtrate, unfiltered rain, neuston (copepods and mixed microcrustaceans), and air filter and polyurethane foam (PUF) samples. Extraction and processing of samples for analysis on the dual-column, dual-detector system followed established and validated procedures (12-15). In summary, the sample preparation included solvent extraction (liquid-liquid extraction for the water samples, Soxhlet extraction for the PUF and filter samples, and Tissuemizer homogenization/extraction for neuston samples), column cleanup and isolation of the PCB/chlorinated pesticide/PAH fraction, concentration, and submission for instrumental analysis. Response factors were determined for each analyte on both column/deMr systems and strict quality control
ANALYTICAL CHEMISTRY, VOL. 62, NO. 17, SEPTEMBER 1, 1990
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IS
, / Y
I
Flgure 1. DB-WECD and DB-l7/ELCD
GC chromatograms of the PCB and pesticide standard.
procedures, that included three point calibration (approximately 20,40, and 80 pg/pL) of each analyte each day of analysis, were followed (15). Analyte response factors were monitored against preestablished criteria of consistency. Laboratory quality control procedures included the processing of a procedural blank and matrix spike and matrix spike duplicate samples with each batch of no more than 12 samples. The procedural blank sample ensured that no significant levels of contamination were introduced, and the matrix spike and matrix spike duplicate samples provided recovery information for each analyte, and thus extraction and sample processing efficiency information, as well as information on the laboratories ability to reproducibly analyze samples. Internal standard recoveries were determined for each sample and tracked against predetermined criteria. Concentrations of analytes initially identified by RRI match on the primary (DB-5) column were calculated by the method of internal standard using TCMX or dibromooctafluorobiphenyl (DBOFB) as the internal standard. Analytes were then identified by RRI on the confirmatory (DB-17)column. The RRI criteria were *O.l RRI unit for identification, on both columns. In addition to RRI matching, the response of the analytes relative to the internal standard on both column/detector systems was compared for confirmation purposes. PCB pattern recognition was also used for identification purposes whenever possible. Analytes identified on both columns were considered confirmed identifications. The detection limit differences between DB5/ECD and DB-l7/ELCD (Table 11) were considered in confirming initially identified analytes. The value of the simultaneous dual-column, dual-detector method was established by evaluating the importance of the added information relative to the additional effort. This evaluation included comparing the number of confirmed identifications with the number of identifications on the primary column, which might have been misidentified by a one-column, one-detector system.
RESULTS AND DISCUSSION Table I lists the elution order and absolute and relative retention times of the PCB and pesticide analytes on the two column/detector systems. Figure 1shows the DBd/ECD and DB-l7/ELCD GC chromatograms for a 3-pL injection of a GC standard, split between the two column/detector systems, with an analyte concentration of approximately 80 pg/pL per analyte. GC retention time characteristics were determined to be constant and reproducible for both the DB-5/ECD and DB-17IELCD. The operation and data reduction of the dual-column, dual-detector system involved only slightly more work than
Table 11. Typical Instrument Detection Limits (IDL) for Pesticides and PCBs on DB-5/ECD and DB-l7/ELCD Systems’
analyte
DB-5/ ECD IDLb 2.1
lindane
cia (8)
C b (28) heptachlor C1, (52) aldrin Cl, (44) heptachlor epoxide c14 (66) o,p’-DDE Cl, (101) a-chlordane trans-nonachlor dieldrin p,p’-DDE c4 (77) O,P ’-DDD
Cl, (118)
p,p’-DDD O,P ’-DDT Cl, (153) C1, (105) p,p’-DDT C& (138) Cl, (126) C1, (187) cl, (128) C11 (180) mirex C11 (170) Cl8 (195) C1, (206)
1.3 0.9 2.5 2.5 3.9 3.1 1.3 2.9 4.2 4.0 3.9 3.6 3.6 3.6 2.5 5.9 10.5 8.1
6.6 5.5 3.7 4.4 5.7 6.6 4.6 7.6 5.5 5.0 5.9 8.4 8.1 8.4 9.2
analyte HCB Clz (8) C1, (18)/lindane heptachlor cb (28) aldrin c4 (52) cc (44) heptachlor epoxide c4 (66) trans-nonachlor Cl, (101) a-chlordane 0,p ’-DDE dieldrin
DB-171 ELCD IDLb 16.6 14.7 15.3c 13.2
15.4 13.4 12.3 15.3 16.5 12.1
20.6 14.5 13.4 10.6 9.0 15.4 17.4 9.T 13.6 16.1 13.4 28.9 16.2 13.gC 16.5 14.5 11.9 11.5 20.9 19.6 7.4
=ThePCB congeners are identified by level of chlorination and the specific congener B.Z. number (e.g., Clz (8) = dichlorobiphenyl (8)). IDLs are given in pg/rL. e The IDL is calculated as half the IDL obtained for both analytes coeluting and is thus an IDL estimate for each analvte individuallv.
a one-column, one-detector system. The reaction tube of the ELCD only needed to be replaced once during the 4 months
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Table 111. DB-B/ECD and DB-l'I/ELCD identifications and Confirmations of Individual PCB Congeners in Different Sample Matrices
Table IV. DB-5/ECD and DB-l'I/ELCD Identifications and Confirmations of Chlorinated Pesticides in Different Sample Matrices
% of DB-5/ DB-171 DB-5/ ECD ELCD confirmed ECD hits no. of hits hits confirmed samples hits
DB-5 I DB-171 DB-5/ no. of ECD ELCD confirmed ECD hits hits confirmed hits samples hits
sample type
55
93
40
73
9 23
1 56
16 109
0 40
0 71
9
2
2
1
50
9
6
10
5
83
18
8
12
6
75
precipitation
3
0
0
0
NA
34
neuston
7
21
30
6
29
97
87
8
67
62
44
66
15 0 119
15 0 112
NA
air, PUF + filter air, PUF air, filter air (total)
1 1
6 0 68
2 0 46
NA
10
7 0 74
268
149
59
61
159
219
98
62
66
76
26
39
9 23
9 75
13 89
0 26
0 34
9
5
6
0
0
9
11
9
0
0
18
16
15
0
0
precipitation
3
1
4
0
0
neuston
7
32
41
11
air, PUF + filter air, PUF air, filter air (total)
8
112
104
1 1
10
17 0 129
61
253
microlayer, filtrate microlayer, filter microlayer (total)
total (all samdes)
sample type
14
14
seawater, filtrate seawater, filter seawater (total)
% of
88 87
of operation. Although the ELCD required somewhat more attention than the ECD, the ELCD operated for long periods of time without maintenance, once the analytical parameters were set. As illustrated in Table 11, the instrument detection limits for the selected analytes were noticably lower for the ECD than the IDLs for the ELCD. The ELCD IDLs were 5-10 times higher than those of the ECD. The higher IDLs of the ELCD suggest that the ELCD has a greater signal variability than the ECD a t low analyte concentrations. However, the difference in IDLs between the two detectors was not much smaller when the signal-to-noise ratio method, rather than the standard deviation method, was used to determine the IDLs. In another study (8),detection limits of PCB for the ELCD were 1.4-7.2 times higher than those of the ECD, depending on the sample matrix. If the sample matrix had been used in determining IDLs of the ECD and ELCD in our work, the IDLs of the two detectors would probably have been less different in some sample matrixes because interferences in the ECD analysis would be higher than in the ELCD analysis. Although the ELCD IDLs were higher than the ECD IDLs in our study, the a n a l e s tentatively identified and quantified by the DB-5/ECD were never below the detection limits of the DB-l7/ELCD. In determination of the IDLs for the ECD and ELCD, the standard deviation for the 34 analytes in five analyses of the low standard mixture was 2-19% for the DB-5/ECD and 13-3470 for the DB-l7/ELCD. Similar precision discrepancies were observed between the ECD and ELCD in PCB analysis by another investigator (8). The standard deviation values represent variability in the split, the injection, and detector response. The ELCD signal variability was lower for higher concentration standards, which were closer to the sample extract concentrations. Each of the different sample types (e.g., seawater filtrates) were evaluated to see which of the analytes identified by DB-5/ECD corresponded to the analytes identified by DB17/ELCD. The PCB analysis results are presented in Table I11 and the chlorinated pesticide analysis results are presented in Table IV. The total number of identifications of the possible 15 pesticides and 19 PCB congeners for a particular
seawater, filtrate seawater, filter seawater (total) microlayer, filtrate microlayer, filter microlayer (total)
total (all samoles) I
29 62
,
sample type were independently determined for each type of analysis, DB-5/ECD and DB-l7/ELCD. With these data, the number of analytes identified by both analysis types was computed and the percentage of analytes confirmed was calculated. The identifications, which were made based on retention time and relative retention index as well as detector response/sample concentration, were unambiguous, good matches of peaks of significant size, and were identified with a high degree of confidence by experienced analysts. As indicated in Table 111, the overall rate of PCB congener confirmation of DB-5/ECD identifications was 59%. However, the rate of confirmation varied significantly between sample matrices. In microlayer and precipitation samples none of the DB-5/ECD 'hits" were confirmed by DB-17/ ELCD. For the seawater and neuston samples 35% and 34% of the PCB congener "hits" were confirmed, respectively. The air samples were the only samples in which Aroclor patterns were detected, and thus a large number of PCB congenen were identified, resulting in a high percentage of confiiation. The presence of Aroclors in the air samples significantly raised the overall average percentage of PCB congener confirmation in this study. It appears that for samples without a clearly identified Aroclor pattern, the percentage of PCB congener c o n f i a t i o n of initial analyte "hits" is likely to be significantly lower than the overall 59% obtained in this work. Table IV lists the chlorinated pesticide confirmation data. On an average 62% of the DB-5/ECD analyte identifications were confirmed by DB-l7/ELCD. The rate of confirmation of chlorinated pesticides varied less with the matrix for chlorinated pesticides than it did for PCBs. An exception was the neuston matrix, for which only 29% of the initially identified pesticides were confiied. For seawater, microlayer, and air samples the average percentage of confirmation of chlorinated pesticides was 71%, 75%, and 62%, respectively. The sample matrix obviously affects the number of interfering peaks and initial analyte identifications by either column/detector system. However, even for "clean" (i.e., low interference) samples, such as microlayer samples, a significant number of analytes could be incorrectly identified without confirmation analysis. As an example, dieldrin was frequently
ANALYTICAL CHEMISTRY, VOL. 62, NO. 17, SEPTEMBER 1, 1990 DE-YECD
1.
DB 17lELCD
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Potentially erroneous analyte identifications in environmental samples can be addressed by implementing analyte confirmation in the laboratory. The simultaneous dual-column, dual-detector method described in this work was found to drastically reduce the risk of false positive identifications without significantly increasing the cost or time of analysis. Although the ECD was more sensitive to halogenated compounds than the ELCD, the ELCD did generally reduce matrix interferences. The ECD, however, is generally simpler to use, is slightly more reliable, and requires less maintenance than the ELCD. If the slightly better halogen screening capability of the ELCD is not important, two ECDs with different chromatographic columns may be the more appropriate system. The DB-5 and DB-17 columns were excellent columns for the types of analyses performed in this work. Both columns were able to separate a large number of analytes in complex matrices with very good reproducibility.
LITERATURE CITED
Figure 2. Region of DB5/ECD and DB-l7/ELCD chromatograms of a neuston sample with an analyte standard superimposed for Menti-
fication purposes. identified by DB-5/ECD in microlayer filter and neuston samples, but was shown to be a matrix interference when it could not be confirmed by DB-l7/ELCD (Figure 2). Similarly, aldrin, which had a perfect DB-17 RRI match in several samples, was not evident on the DB-5 column. Although some matrix specific patterns of interference were observed, to the most part the potential misidentifications were not predictable and would not have been avoided even by an experienced analyst had single-column, single-detector analysis been performed. The results of this work indicate that on an average, nearly twice as many analytes would have been identified had a one-column, one-detector system been used rather than the dual-column, dual-detector system, and in some matrices the discrepancy would have been even greater. There is no reason to believe that misidentifications of this magnitude are rare in environmental analyses when confirmation is not performed.
CONCLUSIONS Sets of GC elution data have been presented for a large number of environmentally important PCB congeners and chlorinated pesticides analyzed using two capillary columns with different stationary phase polarity. The DB-5 and DB-17 columns can be used under similar GC conditions and their different retention characteristics make them suitable for preliminary and confirmatory analysis. As has been shown by this work, compounds such as PCBs and pesticides are probably very frequently misidentified in environmental samples when nonspecific detectors (e.g., ECD) are used without confirmation analysis. The degree of misidentification can be 50%, or greater, in many cases. Such misidentification may occur with both simple and complex sample matrices.
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RECEIVED for review December 26,1989. Revised manuscript received May 21, 1990. Accepted May 30, 1990.
