150
Fish
Phillipson and Puma [459] identified chlorinated methoxybiphenyls as contaminants in fish, and recognised them as potential interferers in their gas chromatography mass spectrometric method for the determination of chlorinated benzo-pdioxins. These workers used a similar sample digestion-clean-up procedure to that
used by Lamparski et al. [458], involving digestion of the fish with alcoholic potassium hydroxide followed by hexane extraction, extraction with concentrated sulphuric acid, and clean-up on alumina and florisil.
Gas chromatography-mass spectrometry of the solvent extracts of carp samples
revealed the presence of a group of xenobiotics (CI 3 , Cl 4 and CIs ring substituted
methoxybiphenyls). These compounds gas chromatographed in the region of C1 3 , Cl 4
and CIs polychlorinated dibenzo-p-dioxins and produced intense molecular ions having the same nominal masses and chlorine isotopic abundances as those observed in
the molecular ion clusters from trichloro-, tetrachloro-, and pentachlorodibenzo-pdioxins. Synthesis of 3,3',4',5-tetrachloro-4-methoxybiphenyl and 2,3',4,4'-tetrachlorO-3-methoxybiphenyl provided model compounds which came through the polychlorinated dibenzo-p-dioxins cleanup procedure, and had gas chromatographic and
mass spectrometric properties consistent with those of the residues recovered from
the fish. The finding of chlorinated methoxybiphenyls as contaminants in fish, combined with the potential for their molecular ions to be mistaken for those from polychlorinated dibenzo-p-dioxins, indicates a need for reappraisal of reported identifications of polychlorinated dibenzo-p-dioxin residues in environmental samples by
selected-ion monitoring gas chromatography-mass spectrometry methods based on
monitoring exclusively for the isotopic molecular ions from polychlorinated dibenzop-dioxins. For reliable identification and quantitation of polychlorinated dibenzo-pdioxins by GLe-low-resolution MS, it might be necessary to examine a sufficient
segment of the mass spectrum of the suspect residue to rule out the presence of
PCMBs (by the absence of fragment ion clusters resulting from losses of CH 3 , CH 3 CO
and CH 3 CO + 2CI from the M+ cluster) and other potential interferences not yet observed.
Paasivirta et al. [460] reported on the occurrence of polychlorinated aromatic
ethers in salmon and fish liver oil. They described an improved clean-up technique
which separated polychlorinated diphenyl ethers, anisoles and veratroles, phenoxyanisoles and biphenylanisoles, dioxins and dibenzofurans, into different fractions.
Compounds from all these groups of substances were detected and, in many cases,
identified.
Mitchum et al. [461] determined 10-30 Ilg kg-l levels of 2,3,7,8 tetrachlorodibenzop-dioxin in various fish samples by a procedure involving the use of a capillary
column gas chromatograph interfaced directly to an atmospheric pressure ionization
mass spectrometer. Isolation of 2,3,7,8 tetrachlorodibenzo-p-dioxin from tissue samples was accomplished via multistep high-pressure liquid chromatography on silica
gel incorporating stable label isotope dilution. Polychlorinated biphenyls were found
not to interfere with 2,3,7,8 tetrachlorodibenzo-p-dioxin analysis at the low ng kg- 1
levels. No mention is made of potential interference by chlorinated methoxy biphenyls as discussed by Phillipson and Puma [459]. Again, ethanolic potassium hydroxide was used to digest fish samples, followed by hexane extraction and clean-up on
charcoal column.
Fish
Phillipson and Puma [459] identified chlorinated methoxybiphenyls as contaminants in fish, and recognised them as potential interferers in their gas chromatography mass spectrometric method for the determination of chlorinated benzo-pdioxins. These workers used a similar sample digestion-clean-up procedure to that
used by Lamparski et al. [458], involving digestion of the fish with alcoholic potassium hydroxide followed by hexane extraction, extraction with concentrated sulphuric acid, and clean-up on alumina and florisil.
Gas chromatography-mass spectrometry of the solvent extracts of carp samples
revealed the presence of a group of xenobiotics (CI 3 , Cl 4 and CIs ring substituted
methoxybiphenyls). These compounds gas chromatographed in the region of C1 3 , Cl 4
and CIs polychlorinated dibenzo-p-dioxins and produced intense molecular ions having the same nominal masses and chlorine isotopic abundances as those observed in
the molecular ion clusters from trichloro-, tetrachloro-, and pentachlorodibenzo-pdioxins. Synthesis of 3,3',4',5-tetrachloro-4-methoxybiphenyl and 2,3',4,4'-tetrachlorO-3-methoxybiphenyl provided model compounds which came through the polychlorinated dibenzo-p-dioxins cleanup procedure, and had gas chromatographic and
mass spectrometric properties consistent with those of the residues recovered from
the fish. The finding of chlorinated methoxybiphenyls as contaminants in fish, combined with the potential for their molecular ions to be mistaken for those from polychlorinated dibenzo-p-dioxins, indicates a need for reappraisal of reported identifications of polychlorinated dibenzo-p-dioxin residues in environmental samples by
selected-ion monitoring gas chromatography-mass spectrometry methods based on
monitoring exclusively for the isotopic molecular ions from polychlorinated dibenzop-dioxins. For reliable identification and quantitation of polychlorinated dibenzo-pdioxins by GLe-low-resolution MS, it might be necessary to examine a sufficient
segment of the mass spectrum of the suspect residue to rule out the presence of
PCMBs (by the absence of fragment ion clusters resulting from losses of CH 3 , CH 3 CO
and CH 3 CO + 2CI from the M+ cluster) and other potential interferences not yet observed.
Paasivirta et al. [460] reported on the occurrence of polychlorinated aromatic
ethers in salmon and fish liver oil. They described an improved clean-up technique
which separated polychlorinated diphenyl ethers, anisoles and veratroles, phenoxyanisoles and biphenylanisoles, dioxins and dibenzofurans, into different fractions.
Compounds from all these groups of substances were detected and, in many cases,
identified.
Mitchum et al. [461] determined 10-30 Ilg kg-l levels of 2,3,7,8 tetrachlorodibenzop-dioxin in various fish samples by a procedure involving the use of a capillary
column gas chromatograph interfaced directly to an atmospheric pressure ionization
mass spectrometer. Isolation of 2,3,7,8 tetrachlorodibenzo-p-dioxin from tissue samples was accomplished via multistep high-pressure liquid chromatography on silica
gel incorporating stable label isotope dilution. Polychlorinated biphenyls were found
not to interfere with 2,3,7,8 tetrachlorodibenzo-p-dioxin analysis at the low ng kg- 1
levels. No mention is made of potential interference by chlorinated methoxy biphenyls as discussed by Phillipson and Puma [459]. Again, ethanolic potassium hydroxide was used to digest fish samples, followed by hexane extraction and clean-up on
charcoal column.