Environ. Sci. Technol. 2001, 35, 3513-3518
Comparison of an Individual Congener Standard and a Technical Mixture for the Quantification of Toxaphene in Environmental Matrices by HRGC/ECNI-HRMS ERIC BRAEKEVELT, GREGG T. TOMY, AND GARY A. STERN* Freshwater Institute, Department of Fisheries and Oceans, Winnipeg, Manitoba R3T 2N6, Canada
Both a technical standard and a recently commercially available standard containing 25 congeners were used to quantify toxaphene in a variety of environmental matrices, using high-resolution gas chromatography/electron capture negative ion high-resolution mass spectrometry (HRGC/ ECNI-HRMS). The purpose was to examine the differences between the two standards and to assess how well the congener standard describes the total toxaphene profile. At a resolving power of ∼11 000 no interferences from other organochlorines were observed. Biotic matrices were enriched in octa- and nonachlorobornanes relative to the technical mixture, whereas abiotic matrices were enriched in hexa- and heptachlorobornanes. The hexa- and heptachlorobornanes were generally overestimated by the weighted response of the technical mixture, whereas the nonachlorobornanes were consistently underestimated. The extent to which the technical mixture over- or underestimates total toxaphene concentrations depends on the distribution of congeners among homologue groups and the abundance of particular congeners. The current 25-congener mixture described only ∼35-75% of the total toxaphene response: more congeners are needed to adequately describe some matrices. Correction factors were developed that will allow laboratories to report reliable concentrations of individual congeners in samples that were quantified using the technical mixture, but they should be applied with caution, as they may be highly instrument dependent.
Introduction Toxaphene (camphechlor) was first introduced as a broadspectrum insecticide in 1945. It was used primarily on cotton, soybeans, and peanuts and by fishery managers to rid lakes of undesirable fish. Toxaphene has been one of the most heavily used chlorinated pesticides in the world, with total global production since 1950 estimated at >1 000 000 tonnes (1). Despite being banned in much of the industrialized world in the mid-1980s, toxaphene residues are readily detectable in a variety of environmental matrices. Toxaphene can be transported atmospherically and is now a widespread contaminant in the Arctic (2). It is a continued concern because of its persistence and high bioaccumulation potential (3). * Corresponding author phone: (204) 984-6761; fax (204) 9842403; e-mail:
[email protected]. 10.1021/es0018567 CCC: $20.00 Published on Web 08/08/2001
Published 2001 by the Am. Chem. Soc.
TABLE 1. IUPAC Names, Andrews-Vetter (AV) Codes, and Other Common Names of Individual Toxaphene Congeners in the Congener Standard IUPAC namea
AV code
2-exo,3-endo,6-exo,8,9,10-HxCB 2-endo,3-exo,5-endo,6-exo,8,9,10-HpCB 2-exo,3-endo,5-exo,8,9,10,10-HpCB 2,2,5,5,8,9,10-HpCB 2,2,5-endo,6-exo,8,9,10-HpCB 2-exo,3-endo,6-exo,8,9,10,10-HpCB 2-exo,3-endo,5-exo,6-exo,8,9,10-HpCB 2-exo,5-exo,6-endo,8,9,10,10-HpCB 2-endo,3-exo,5-endo,6-exo,8,8,10,10-OCB
B6-923 B7-1001 B7-1450 B7-495 B7-515 B7-1474 B7-1440 B7-1059 B8-1413
other names Hx-sed Hp-sed
P32, Tox B
P26, T2, Tox 8 2,2,5,5,9,9,10,10-OCB B8-789 P38 2,2,3-exo,5-endo,6-exo,8,9,10-OCB B8-531 P39, TS2 2-endo,3-exo,5-endo,6-exo,8,9,10,10-OCB B8-1414 P40, TS3 2-exo,3-endo,5-exo,8,9,9,10,10-OCB B8-1945 P41 2,2,5-endo,6-exo,8,8,9,10-OCB B8-806 P42a, Tox A 2-exo,5,5,8,9,9,10,10-OCB B8-2229 P44 2,2,5-endo,6-exo,8,9,10,10-OCB B8-810 P49a 2-endo,3-exo,6-exo,8,8,9,10,10-OCB B8-1471 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10B9-1679 P50, T12, NCB Tox Ac, Tox 9 2,2,3-exo,5,5,9,9,10,10-NCB B9-718 2,2,3-exo,5-endo,6-exo,8,9,10,10-NCB B9-743 2-exo,3,3,5-exo,6-endo,8,9,10,10-NCB B9-2006 2,2,5-endo,6-exo,8,8,9,10,10-NCB B9-1046 P56 2,2,3-exo,5,5,8,9,10,10-NCB B9-715 P58 2,2,5,5,8,9,9,10,10-NCB B9-1025 P62 a HxCB, hexachlorobornane; HpCB, heptachlorobornane; OCB, octachlorobornane; and NCB, nonachlorobornane.
Technical toxaphene is produced by the chlorination of camphene and is a complex mixture of ∼200 compounds, consisting primarily of hexa- to nonachlorinated bornanes as well as small quantities of unsaturated components such as chlorinated camphenes and bornenes (4). The technical toxaphene mixture is not completely resolvable even by highresolution GC columns, and many toxaphene peaks coelute with other chlorinated contaminants, including polychlorinated biphenyls (PCBs) and chlordane compounds. Early quantitative methods relied extensively on gas chromatography with electron capture detection (GC-ECD), which required extensive extract cleanup to reduce interferences from other organochlorine compounds. Increased selectivity was achieved by use of mass spectrometry (MS) in the electron ionization (EI) selective ion monitoring (SIM) mode but lacked sensitivity because of extensive ion fragmentation (5). Currently, the most common method for toxaphene analysis is GC-MS in the SIM mode under electron capture negative ionization (ECNI) conditions. Total toxaphene can be determined by summing the total area of all peaks and subtracting known interferences such as chlordanes (6). This method is time-consuming [although it can be automated (7)] and subject to interference by unknown compounds. The use of high-resolution mass spectrometry (HRMS) eliminates interferences from chlordanes and PCB-oxygen adducts and the need for extensive mathematical corrections (8). Analysis can be greatly simplified by selecting several “marker peaks” from the technical mixture, which are summed to determine total toxaphene (8, 9). However, many important toxaphene congeners are only minor components of the technical material or coelute VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Ions Used for Selected Ion Monitoring (SIM) of Hexa- to Nonachlorobornanes congener group C10H12Cl6 C10H11Cl7 C10H10Cl8 C10H9Cl9
[13C8]mirex
quantitation ion
confirmation ion
[M - Cl](308.9352) [M - Cl](342.8962) [M - Cl](376.8573) [M - Cl](412.8153) [M - HCl - Cl](374.8416) [M - 4Cl](409.7747)
[M - Cl](310.9323) [M - Cl](344.8933) [M - Cl](378.8543) [M - Cl](410.8183) [M - HCl - Cl](376.8387) [M - 4Cl](411.7718)
SIM windowa 1, 2 1, 2, 3 2, 3, 4 3, 4
4
a SIM windows (60 m DB-5MS column, 0.25 mm i.d., 0.25 µm film thickness): 1, 20-25 min; 2, 25-28 min; 3, 28-31 min; 4, 31-35 min.
with environmentally irrelevant congeners (8, 10-12), making marker peak selection difficult. The results obtained using this method are highly dependent on the number of marker peaks selected (9). In the absence of individual congener standards to match those observed in environmental samples, quantification of toxaphene is generally done using the technical mixture as an analytical standard. However, peak profiles in environmental samples often differ significantly from the industrial mixture, due to differing accumulation and decomposition behavior of individual congeners. The calculation of an average weighted response factor for individual congeners from the technical mixture can result in significant errors in quantitation because of the highly variable ECNIMS response of different toxaphene congeners (5, 13, 14). The magnitude of these errors would be expected to increase with decreasing similarity of an environmental sample to the technical mixture. The composition of the technical mixture can also vary depending on the manufacturer and lot number (15). In addition, the determination of detection limits in a
technical mixture is difficult, because as the concentration decreases, minor components fall below the detection limit while more abundant components remain detected (8). Efforts have been made to quantify toxaphene on the basis of individual congeners, which only recently have become available commercially. However, because all congeners observed in environmental samples are not yet available, technical toxaphene is still needed to estimate total toxaphene concentrations in environmental matrices. In this study, we determined toxaphene in environmental matrices by high-resolution gas chromatography (HRGC) coupled with ECNI HRMS. Samples were quantified using both a technical standard and a recently commercially available standard containing 25 congeners, with the purpose of examining the differences between the two standards. We compared different matrices to assess how well the congener standard describes the total toxaphene profile and developed correction factors that will allow laboratories to report reliable concentrations of individual congeners in samples that were quantified using the technical mixture.
Experimental Section Materials. Glass-distilled grade dichloromethane (DCM), isooctane, and hexane were obtained from Caledon Laboratories (Georgetown, ON, Canada). Technical toxaphene in isooctane was purchased from Radian International (Austin, TX). A toxaphene standard (Tox 482) consisting of 25 individual toxaphene congeners in isooctane was graciously provided by Promochem (Wesel, Germany). IUPAC and common names of the congeners present in this standard mixture are shown in Table 1. Isotopically labeled [13C8]mirex was purchased from Cambridge Isotope Laboratories Inc. (Andover, MA). Sample Extraction and Cleanup. Invertebrates (Cyclocaris guilelmi) from the Beaufort Sea, air samples from Alert (Northwest Territory, Canada), and lake trout (Salvelinus namaycush) from Lake Laberge (Yukon, Canada) were collected in 1998. Beluga (Delphinapterus leucas) blubber samples were collected from Igloolik (Nunavut, Canada) in
TABLE 3. Fragmentation Patterns and Relative Retention Times (RRT) of Toxaphene Congeners in the Promochem Standard fragmentation (%) [M - Cl - HCl]-
[M - 2HCl]-
11.4 2.6 2.5 2.1
2.0 5.1 4.5
0.6 0.5
27.2
2.0
14.3
1.7
0.871
65.2
1.0
4.0
0.905 0.900 0.908 0.910 0.910 0.916 0.922 0.943 0.944 0.954 0.955 0.969 0.969 0.969 0.979 1.000
8.8 41.3 35.6 37.6 50.0 50.4 27.1 38.7 35.4 33.2 31.0 50.9 45.5 22.5 68.2
2.9 0.7 0.9
1.1 4.5 3.5 4.4 8.1 7.2 22.7 40.1 5.0
[M -
Cl]-
AV code
RRTa
B6-923 B7-1001 B8-1413 B7-1450 B7-495 B7-515 B7-1474 B7-1440 B8-789 B7-1059 B8-531 B8-1414 B8-1945 B8-806 B8-2229 B8-810 B9-1679 B9-718 B8-1471 B9-743 B9-2006 B9-1046 B9-715 B9-1025
0.769 0.799 0.835 0.855
58.8 50.3 32.2 44.3
0.866
[M -
HCl]-
6.2
5.2 1.4 5.7 34.5 2.6 24.9
[M - 2Cl - HCl]-
[M - 3Cl]-
11.8 2.1 1.8 1.5 1.2
0.6
1.4 4.3 15.8
a RRTs determined on a 60 m × 0.25 mm o.d. DB-5MS capillary column (0.25 µm film thickness). Oven temperature program: 80 °C (2 min), 20 °C/min to 200 °C, 2 °C/min to 230 °C, 10 °C/min to 300 °C, hold 8 min.
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1995. A sediment core from the south basin of Lake Winnipeg, a large oligotrophic lake receiving both atmospheric and riverine toxaphene inputs, was taken in 1999. Sample extraction and cleanup procedures are provided in detail elsewhere (16-20). Briefly, surface sediments and invertebrates were freeze-dried, combined with anhydrous sodium sulfate, and extracted in an accelerated solvent extractor (ASE, Dionex Canada Ltd., Oakville, ON, Canada) (20). PCB 30 and octachloronaphthalene recovery standards were added before extraction. Sulfur was removed by treatment of the extracts with activated copper powder (19). Blubber was combined with anhydrous sodium sulfate and extracted in a ball mill (16). Frozen fish muscle was ground cryogenically, combined with anhydrous sodium sulfate, and Soxhlet extracted with 50% DCM in hexane. Fish extracts were subjected to gel permeation chromatography (GPC) to remove lipids (17). Extracts were fractionated on 1.2% deactivated Florisil (18). Fractions 1 and 2, which contained toxaphene components, were combined. A known amount of [13C8]mirex was added as an internal standard prior to GC-MS analysis to correct for variations in MS performance between injections. GC-MS. All analyses were performed on a Hewlett-Packard 5890 series II gas chromatograph, fitted with a 60 m × 0.25 mm i.d. (0.25 µm film thickness) DB-5MS capillary column (Chromatographic Specialties, Brockville, ON, Canada), connected through a heated transfer line maintained at 280 °C to a Kratos Concept high-resolution mass spectrometer (EBE geometry) controlled by a Mach 3X data system. Helium was used as the carrier gas. Splitless injections of 2 µL were made by a CTC A200SE autosampler, with the injector temperature set at 250 °C. The initial column temperature was 80 °C; at 2 min the oven was ramped at 20 °C min-1 to 200 °C, then at 2 °C min-1 to 230 °C, then at 10 °C min-1 to a final temperature of 300 °C, and held for 8 min. Electronic pressure programming was used to increase the pressure during the injection cycle (21) and then to maintain a constant flow of 1 mL/ min during the remainder of the run. ECNIMS was performed at an ion source temperature of 120 °C, an initial electron beam energy of 180 eV, and an ion accelerating voltage of 5.3 kV. The moderating gas was argon at a pressure of ∼2 × 10-4 Torr, as measured by the source ion gauge. Full-scan ECNI mass spectra were scanned at 1 s/decade over the mass range m/z 65-500. SIM was performed at a resolving power of ∼11 000, with perfluorokerosene (PFK) used as the mass calibrant. The cycle time for each window was 1 s, with an equal dwell time for each monitored ion. The two most abundant ions in the [M - Cl]cluster of each chlorine homologue group were monitored. For B9-1025, the intensity of the [M - Cl]- cluster is very low (5): the [M - HCl - Cl]- ion cluster was monitored instead. The most abundant ion was used for quantitation and the next most abundant as a confirmation ion. The ions monitored in each window are shown in Table 2. Quantitation. Individual congeners in environmental samples were identified by matching retention times to the congener standard and confirmed if quantitation and confirmation ions comaximized and were within 15% of the isotope ratio found in the standard. Individual congeners were quantified by comparing the peak area of each congener in the sample to that of the individual congener standard, after both sample and standard had been corrected for differences in [13C8]mirex response. Individual congener concentrations in the environmental samples were also determined using the average weighted response factor of the technical mixture. Homologue concentrations were determined by comparing the total area of all peaks in a particular homologue group in the sample to that in the technical mixture, with total toxaphene the sum of hexa- to nonachlorinated homologue groups.
FIGURE 1. Total ion chromatograms (sum of hexa- to nonachlorinated bornanes) of (A) Arctic air, (B) Lake Winnipeg sediments, (C) Arctic invertebrates, (D) Yukon lake trout, (E) beluga whale blubber, and (F) technical toxaphene.
TABLE 4. Relative Percent Distribution among Chlorine Homologue Groups in Technical Toxaphene and Environmental Media technical mixture air sediments invertebrates lake trout blubber
hexa-
hepta-
octa-
nona-
1.4 3.8 31.2 1.2 0.4 0.4
26.6 41.2 39.8 19.2 11.8 15.4
63.1 48.3 25.6 68.0 69.3 67.5
8.9 6.7 3.5 11.6 18.5 16.7
Potential Interferences. The effects of other halogenated organochlorines as potential interferences at a resolving power of 1000 have been discussed in detail elsewhere (6). At a resolving power >10 000, interferences from chlordanes and PCB-oxygen adducts are negligible (8). Technical chlordane, a mixture of 87 PCB congeners (Ultra Scientific, North Kingstown, RI), a mixture of organochlorine pesticides (SRM 2261; NIST, Gaithersburg, MD), and short (C10-C13) and medium (C14-C17) polychlorinated n-alkanes (PCAs) were injected using the above toxaphene method. At a VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 5. Comparison of Concentrations of Toxaphene Congeners in Environmental Media, Determined Using both the Average Weighted Response of Technical Toxaphene (tech) and the Congener Standard (cong) air (pg/m3)
sediments (pg/g of dw)a
invertebrates (ng/g of dw)a
lake trout (ng/g of ww)a
blubber (ng/g of ww)a
tech
cong
tech
cong
tech
cong
tech
cong
tech
B6-923 B7-1001 B7-1450 B7-495 and B7-515b B7-147 and B7-1440b B7-1059
0.087 0.43 0.056 0.020 0.057 0.001
0.038 0.35 0.072 0.084 0.013 0.002
4.4 2.4 0.25 0.19 1.3 0.054
2.1 1.8 0.29 2.3 0.90 0.14
0.35 1.8 0.60 ndc 1.1 0.096
0.12 1.0 0.64 ndc 0.36 0.16
0.018 0.28 0.057 0.036 0.054 ndc
0.009 0.18 0.057 0.20 0.018 ndc
0.66 4.4 2.2 0.42 3.7 0.15
total hexa- and hepta-
0.65
0.55
8.6
7.6
3.9
2.3
0.45
0.46
11.5
10.0
B8-1413 B8-789 B8-531 B8-1414 and B8-1945b B8-806 B8-2229 B8-810 B8-1471
0.80 0.066 0.068 0.19 0.16 0.30 0.045 0.011
2.0 0.19 0.063 0.081 0.22 0.88 0.17 0.021
0.13 0.30 0.33 0.31 0.55 1.0 0.24 0.22
0.21 0.32 0.31 0.42 0.36 1.7 0.56 0.35
2.9 0.49 4.6 3.1 1.8 7.6 0.75 1.0
4.8 0.71 3.1 2.0 1.4 11.4 2.5 1.7
1.4 0.17 0.53 0.77 0.93 2.3 0.44 0.27
2.4 0.18 0.38 0.55 0.59 3.1 1.2 0.39
8.0 2.3 16.6 7.5 11.3 27.6 5.8 4.2
15.2 2.3 5.2 5.4 7.1 44.4 13.1 6.8
total octa-
1.6
3.6
3.1
4.2
27.5
6.8
8.8
83.2
99.4
B9-1679 B9-718 B9-743, B9-2006, and B9-1046b B9-715 B9-1025
0.39 0.001 0.002 0.004 0.004
0.59 0.009 0.028 0.029 0.26
0.43 0.014 0.057 0.061 ndc
0.59 0.17 1.9 0.16 ndc
3.8 ndc 0.066 0.14 0.064
2.4 ndc 0.004 0.072 0.074
9.5 ndc 0.047 0.54 2.5
19.3 ndc 0.58 2.4 0.075
29.4 ndc 10.3 7.3 2.3
total nona-
0.40
0.92
0.57
2.8
4.0
11.9
2.6
12.7
22.4
49.3
14.5
30.3 66.5
41.8
9.8 58.1
21.9
117 64.6
total congeners % of total toxaphene responsed
2.7 37.1
5.1
12.2 74.4
22.3
7.7 ndc 1.0 0.69 2.5
cong 0.30 2.9 2.3 2.9 1.4 0.32
159
a ww, wet weight; dw, dry weight. b These congeners coelute and are reported together. c nd, not detected. Instrument detection limits (pg, S:N ) 5): B7-495 and B7-515, 0.46; B7-1059, 1.4; B8-2229, 0.48; B9-718, 0.35; B9-1025, 1.8. d Pecent of total toxaphene response ) total peak area of the congeners ÷ total peak area of all toxaphene peaks × 100.
resolving power of 11 000, no interferences with toxaphene ions were detected. The presence of naturally occurring 13C results in other toxaphene fragments, such as [M - HCl]-, that can interfere with the [M - Cl]- ions. The mass of 13C is 4.5 mDa less than that of 12CH, and a resolving power of ∼70 000 is needed to exclude any overlap between [M - HCl]- and [M - Cl]-. However, the maximum abundance of the [M - HCl]- cluster relative to [M - Cl]- is 20% (Table 3). The maximum contribution of the [M - HCl]- cluster to [M - Cl]- is therefore 20% × (10 carbon atoms/molecule) × (natural 13C/12C ratio ) 1.1%) ) 2.2%. It is not necessary to apply a correction factor for this small potential contribution. Similarly, loss of HCl2 from a higher homologue group can interfere with the [M - Cl]- ion cluster. For some congeners, such as B8-810, the [M - HCl - Cl]- ion cluster is significant, but these peaks would be rejected from lower homologue groups because the ratio of quantitation to confirmation ions would be outside the acceptable range. Quality Control. Precautions used in the analysis of toxaphene include use of glass-distilled solvents and baking of glassware, sodium sulfate, and Florisil. A procedural blank, which was taken through all phases of extraction and cleanup, was included with each batch of samples. Quantitative results are regularly compared with those of other laboratories through participation in interlaboratory exercises for the analysis of chlorinated contaminants (including toxaphene) and by the use of standard reference materials. The linearity of ECNIMS response over the concentration range of 0.1-100 pg/µL was tested using the congener standard. Correlation coefficients (R2) of >0.96 were obtained 3516
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for all congeners with the exception of B8-531, which partially coelutes with B8-1414 and B8-1945.
Results and Discussion Toxaphene Profiles. The environmental matrices examined had different toxaphene profiles (Figure 1; Table 4). Biotic matrices were enriched in octa- and nonachlorobornanes relative to the technical mixture, whereas abiotic matrices were enriched in hexa- and heptachlorobornanes (Table 4). The distribution among chlorine homologue groups reflects the change in toxaphene composition due to physical or biological transformation of the technical mixture. Air contained the most volatile compounds, and a high number of the toxaphene peaks in these samples were not found in the congener standard (Table 5). Toxaphene in lake sediments, on the other hand, undergoes extensive microbial degradation and therefore has a much simpler profile (22). Approximately 75% of the total toxaphene response in the sediments was described by the congener standard. The biotic matrices were similarly described by the congener standard, at ∼55-65% of the total toxaphene peak area. These values are somewhat lower than those reported by others (23), who found that six toxaphene congeners accounted for at least 80-85% of the total toxaphene response. We suggest that this high percentage may be due to a large number of minor components falling below the instrument detection limit. In interlaboratory studies our congener-specific results agree well with those of other laboratories, but we consistently report higher total toxaphene concentrations (T. F. Bidleman, unpublished results), possibly because a higher number of minor components remain detectable.
FIGURE 2. HRGC/ECNI-HRMS elution profiles of monitored ions in (A) technical toxaphene and (B) individual congener standard aligned to show the four time windows used. All congeners in the congener standard are of equal concentration. Comparison of Standards. Results of quantitation using the two standards are presented in Table 5. In general, the hexa- and heptachlorobornanes were overestimated by the average weighted response of the technical mixture. The nonachlorobornanes were consistently underestimated and were generally the least accurately quantified homologue group. Quantitation differences between the two standards are most likely due to the appreciable differences in ECNIMS response of congeners within the same homologue group (Figure 2). The extent to which the technical mixture over- or underestimates total toxaphene concentrations depends on the distribution of congeners among homologue groups and the abundance of particular congeners. Sediments, for instance, were dominated by B6-923 and B7-1001, both of which were overestimated by the technical standard. This resulted in an overestimation of total toxaphene in sediments if the technical standard was used for quantitation. In contrast, total toxaphene concentrations in biotic matrices, which were enriched in nonachlorobornanes, were under-
estimated by the weighted response factor of the technical mixture. Correction Factors. There were consistent differences among environmental matrices in the quantitation of particular congeners. The ratio of sample concentration calculated by the congener standard to that of technical toxaphene (C/T ratio) is effectively a direct comparison of the technical and congener standards. There were no differences in C/T ratios among different matrices: the peak area of the sample is in both the numerator and denominator and therefore cancels out. The correction factors presented in Table 6 should be applied with caution, as they may be highly instrument dependent. Fragmentation in ECNIMS varies considerably with ion source temperature (24), which is not well controlled on some instruments (5). We also use argon as a moderating gas, whereas many other laboratories use methane. Both ion source temperature and moderating gas differences could change relative abundances of monitored ions, which may affect the presented correction factors. VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 6. Correction Factors (Ratio of Sample Concentration Calculated by the Congener Standard to That of Technical Toxaphene) for Toxaphene Congeners congener
correction factor
% RSD
B6-923 B7-1001 B8-1413 B7-1450 B7-495 and B7-515a B7-1474 and B7-1440a B8-789 B7-1059 B8-531 B8-1414 and B8-1945a B8-806 B8-2229 B8-810 B9-1679 B9-718 B8-1471 B9-743, B9-2006, and B9-1046a B9-715 B9-1025
0.45 0.67 1.8 1.1 4.8 0.35 2.3 1.0 0.77 1.6 0.62 1.6 2.3 1.6 15 1.5 10.7 4.9 34
7.7 10.6 16.1 9.9 10.0 10.4 12.1 7.2 33.4 91.1 7.3 13.4 3.6 35.1 43.7 9.1 33.0 65.7 12.3
a
These congeners coelute and are reported together.
The correction factors generally showed good reproducibility (Table 6). Many that had high (>20% RSD) variability were coeluting groups of congeners. Interestingly, if an octachlorobornane coeluted with a nonachlorobornane (B8810 and B9-1679; B9-718 and B8-1471), it was the nonachlorobornane that showed the highest correction factor variability. The coelution of many congeners leads us to recommend that a GC column other than 5% diphenyl poly(dimethylsiloxane) (DB-5) be used. Vetter et al. (11) reported separation of B8-1414 and B8-1945 on a CP-Sil 2 column. The variability of these correction factors may decrease if the congeners are adequately separated. This method will be improved as more congeners become available. The current 25-congener mixture described only ∼35-75% of the total toxaphene response: clearly, more congeners are needed to adequately describe some matrices. In addition, the availability of isotopically labeled toxaphene congeners would increase the robustness of this method by allowing internal standards to be placed in all SIM windows, similar to EPA methods for the analysis of chlorinated dioxins and furans.
Acknowledgments We are grateful to Ulrich Berger (Promochem) for providing the congener standard and to Brian Billeck (Freshwater
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Institute) and Vladimir Nikiforov (St. Petersburg University, Russia) for their technical assistance.
Literature Cited (1) Voldner, E. C.; Li, Y. F. Chemosphere 1993, 27, 2073-2078. (2) Bidleman, T. F.; Patton, G. W.; Walla, M. D.; Hargrave, B. T.; Vass, W. P.; Erickson, P.; Fowler, B.; Scott, V.; Gregor, D. J. Arctic 1989, 42, 307-313. (3) Fisk, A. T.; Rosenberg, B.; Cymbalisty, C. D.; Stern, G. A.; Muir, D. C. G. Chemosphere 1999, 39, 2549-2562. (4) Kimmel, L.; Coelhan, M.; Leupold, G.; Vetter, W.; Parlar, H. Environ. Sci. Technol. 2000, 34, 3041-3045. (5) Lau, B.; Weber, D.; Andrews, P. Chemosphere 1996, 32, 10211041. (6) Swackhamer, D. L.; Charles, M. J.; Hites, R. A. Anal. Chem. 1987, 59, 913-917. (7) Glassmeyer, S. T.; Shanks, K. E.; Hites, R. A. Anal. Chem. 1999, 71, 1448-1453. (8) Fowler, B. Chemosphere 2000, 41, 487-492. (9) Fowler, B.; Hoover, D.; Hamilton, M. C. Chemosphere 1993, 27, 1891-1905. (10) Muir, D. C. G. Chemosphere 1993, 27, 1827-1834. (11) Vetter, W.; Krock, B.; Luckas, B. Chromatographia 1997, 44, 65-73. (12) Shoeib, M.; Brice, K. A.; Hoff, R. M. Chemosphere 2000, 40, 201211. (13) Vetter, W.; Luckas, B. Rapid Commun. Mass Spectrom. 1998, 12, 312-316. (14) Shoeib, M.; Brice, K. A.; Hoff, R. M. Chemosphere 1999, 39, 849871. (15) Howdeshell, M. J.; Hites, R. A. Environ. Sci. Technol. 1996, 30, 220-224. (16) Grussendorf, O. W.; McGinnis, A. J.; Solomon, J. J. Assoc. Off. Anal. Chem. 1970, 53, 1048-1054. (17) Stalling, D. L.; Tindle, R. C.; Johnson, J. L. J. Assoc. Off. Anal. Chem. 1972, 55, 32-38. (18) Norstrom, R. J.; Simon, M.; Muir, D. C. G.; Schweinsburg, R. E. Environ. Sci. Technol. 1988, 22, 1063-1071. (19) Muir, D. C. G.; Omelchenko, A.; Grift, N. P.; Savoie, D. A.; Lockhart, W. L.; Wilkinson, P.; Brunskill, G. J. Environ. Sci. Technol. 1996, 30, 3609-3617. (20) Tomy, G. T.; Stern, G. A. Anal. Chem. 1999, 71, 4860-4865. (21) Bartha, R.; Vetter, W.; Luckas, B. Fresenius’ J. Anal. Chem. 1997, 358, 812-817. (22) Stern, G. A.; Loewen, M. D.; Miskimmin, B. M.; Muir, D. C. G.; Westmore, J. B. Environ. Sci. Technol. 1996, 30, 2251-2258. (23) Kimmel, L.; Angerho¨fer, D.; Gill, U.; Coelhan, M.; Parlar, H. Chemosphere 1998, 37, 549-558. (24) Stemmler, E. A.; Hites, R. A. Anal. Chem. 1985, 57, 684-692.
Received for review November 8, 2000. Revised manuscript received May 14, 2001. Accepted June 18, 2001. ES0018567
