Quantification of toxaphene residues in fish and fish products using a new analytical standard

Toxaphene, the most heavily used chlorinated hydrocarbon insecticide, is difficult to quantify, because it is a mixture of more than 200 compounds, primarily polychlorinated bornanes^1-5). These components elute over a wide range of GC retention times and are not completely resolvable even by capillary columns. Interferences with other organochlorine contaminants cannot be excluded^6-8). Some of the interfering compounds can be eliminated by adsorption column chromatography^9,10). Unfortunately, any additional clean-up procedure reduces recoveries, causes poor reproducibility and thus, compromises accuracy and sensitivity. Selectivity can be achieved by use of negative ion mass spectrometry - selected ion monitoring (NICI-SIM)^11-14). The GC analyses of environmental samples are furthermore complicated by changes in the original composition of the chlorobornanes due to chemical and metabolic conversions⁹⁾. Differences in the degree of chlorination or in positional isomerization influence NICI-SIM response significantly⁸⁾. Quantification using a technical standard can therefore lead to erroneous results. Considering conversion and accumulation processes of toxaphene components in the environment, we have prepared a chlorobornane mixture, yielding a GC-NICI-SIM chromatogram, which resembles very much that of the residues obtained from different fish tissues. It was demonstrated, that this mixture can be used as representative standard for the exact quantification of toxaphene residues in fish and fish products.