148
Fish
nor widespread a contaminant of seafood as are PCBs and DDT. This does not
correspond to earlier seafood studies [449-451], which reported that mirex occurred
much more frequently and densely in many of these same collection sites. Probably
the reason for the discrepancy between their study and earlier studies is the confusion
of Aroclor 1260 with mirex. The retention time for the last peaks of Aroclor 1260 is
almost identical to the retention time for mirex on most columns routinely used for
analysing mirex [448]. Unless extensive additional clean-up procedures are employed,
such as those used by Markin et al. [445] it is almost impossible to separate these two
peaks. In their study, if the problem of PCB confusion had not been recognized and
the special clean-up procedure used, the PCB peaks probably would have been reported as mirex.
Kaiser [452] used gas chromatography-mass spectrometry to identify mirex in
fishes in Lake Ontario, Canada. Under standard gas chromatographic conditions, the
peak due to this substance is superimposed on that of the PCBs and, as a result, the
presence of mirex may have been unrecognized and may therefore have been misinterpreted, as a PCB isomer by previous workers. The fish samples were digested with
sulphuric acid. The purified extracts were analysed for their PCB contents by two
parallel means:
(1) quantitative determination of PCBs by gas chromatography with electron capture
detectors [453-455]; and
(2) qualitative investigation of the gas chromatographic peaks by computerized gas
chromatography-mass spectrometry [455].
One of the PCB peaks was found with a mass spectrometric fragmentation pattern
different from that of known PCB isomers. The base peak of this compound had a
mass-to-charge ratio (m / e) of 272 with an isotope cluster centred on this peak,
unambiguously indicating a (C s C1 6 )+ moiety. Mass spectrometric fragmentations showing this cluster are derived from compounds containing a perchlorocyclopentadiene
unit in their molecule structure or, for a very few cases, from similar, highly chlorinated hydrocarbons. Compounds of this kind include such insecticides as aldrin, chlordane, dieldrin, endrin, endosulfan, heptachlor, kepone, mirex, pentac, and toxaphene.
The identification of the unknown in the fish samples as mirex was established by a
combination of gas chromatographic and mass spectrometric techniques.
Laseter et al. [456] also used a gas chromatography-mass spectrometry system to
determine mirex in lake Ontario fish samples. Quantitative analyses employing
reconstructed mass chromatograms with the mirex (perchloropentacyc10[5.3.0.0 2 . 6 .0 4 . 8 ] decane or dodecachlorooctahydro-1.3.4-metheno-2H-cyclobuta[c,d]pentalene) base peak (m/ e 272) and gas chromatography with electron capture and Hall electrolytic detectors providing concentration values ranging from
0.15 to 0.33 mg kg- 1 fresh weight of tissue. However, the technique of selective ion
monitoring or mass fragmentography using high mass ion fragments exclusively
associated with mirex demonstrates that the actual mirex concentrations are from
three to six times lower.
Onuska et al. [457] analysed lake trout and lamprey samples from Lake Ontario, to
provide a rapid, quantitative procedure for the determination of mirex. Statistically
insignificant differences were found, based on the correlation of results from linear
Fish
nor widespread a contaminant of seafood as are PCBs and DDT. This does not
correspond to earlier seafood studies [449-451], which reported that mirex occurred
much more frequently and densely in many of these same collection sites. Probably
the reason for the discrepancy between their study and earlier studies is the confusion
of Aroclor 1260 with mirex. The retention time for the last peaks of Aroclor 1260 is
almost identical to the retention time for mirex on most columns routinely used for
analysing mirex [448]. Unless extensive additional clean-up procedures are employed,
such as those used by Markin et al. [445] it is almost impossible to separate these two
peaks. In their study, if the problem of PCB confusion had not been recognized and
the special clean-up procedure used, the PCB peaks probably would have been reported as mirex.
Kaiser [452] used gas chromatography-mass spectrometry to identify mirex in
fishes in Lake Ontario, Canada. Under standard gas chromatographic conditions, the
peak due to this substance is superimposed on that of the PCBs and, as a result, the
presence of mirex may have been unrecognized and may therefore have been misinterpreted, as a PCB isomer by previous workers. The fish samples were digested with
sulphuric acid. The purified extracts were analysed for their PCB contents by two
parallel means:
(1) quantitative determination of PCBs by gas chromatography with electron capture
detectors [453-455]; and
(2) qualitative investigation of the gas chromatographic peaks by computerized gas
chromatography-mass spectrometry [455].
One of the PCB peaks was found with a mass spectrometric fragmentation pattern
different from that of known PCB isomers. The base peak of this compound had a
mass-to-charge ratio (m / e) of 272 with an isotope cluster centred on this peak,
unambiguously indicating a (C s C1 6 )+ moiety. Mass spectrometric fragmentations showing this cluster are derived from compounds containing a perchlorocyclopentadiene
unit in their molecule structure or, for a very few cases, from similar, highly chlorinated hydrocarbons. Compounds of this kind include such insecticides as aldrin, chlordane, dieldrin, endrin, endosulfan, heptachlor, kepone, mirex, pentac, and toxaphene.
The identification of the unknown in the fish samples as mirex was established by a
combination of gas chromatographic and mass spectrometric techniques.
Laseter et al. [456] also used a gas chromatography-mass spectrometry system to
determine mirex in lake Ontario fish samples. Quantitative analyses employing
reconstructed mass chromatograms with the mirex (perchloropentacyc10[5.3.0.0 2 . 6 .0 4 . 8 ] decane or dodecachlorooctahydro-1.3.4-metheno-2H-cyclobuta[c,d]pentalene) base peak (m/ e 272) and gas chromatography with electron capture and Hall electrolytic detectors providing concentration values ranging from
0.15 to 0.33 mg kg- 1 fresh weight of tissue. However, the technique of selective ion
monitoring or mass fragmentography using high mass ion fragments exclusively
associated with mirex demonstrates that the actual mirex concentrations are from
three to six times lower.
Onuska et al. [457] analysed lake trout and lamprey samples from Lake Ontario, to
provide a rapid, quantitative procedure for the determination of mirex. Statistically
insignificant differences were found, based on the correlation of results from linear