Enrichment of chlorinated fatty acids in fish lipids prior to analysis by capillary gas chromatography with electrolytic conductivity detection and mass spectrometry

Chlorinated carboxylic acids of fatty acid character have been shown to account for up to 90% of the extractable, organically bound chlorine (EOCl) in fish. To facilitate the detection of chlorinated fatty acid methyl esters (FAMEs) released from fish lipids, an enrichment was performed by removing the polyunsaturated FAMEs and saturated, straight-chain FAMEs through their complexation with silver ions and urea, respectively. The resulting about 30-fold increase in the concentration of chlorinated FAMEs allowed for their analysis, by gas chromatography (GC) with halogen-selective electrolytic conductivity detection, in lipids containing only 30 ppm (m/m) of EOCl. Following additional purification by thin-layer chromatography, methyl esters of dichlorotetradecanoic, dichlorohexadecanoic and dichlorooctadecanoic acids were indicated by GC-ammonia positive ion chemical ionisation mass spectrometry in a fish sample containing 1200 ppm (m/m) of EOCl.