HALOGENATED FATTY-ACIDS .2. METHODS OF DETERMINATION IN LIPIDS

Halogenated fatty acids are the major contributors to organohalogen co mpounds in lipids of marine mammals, fish, and bivalves. For the initi al characterization of these recently noticed compounds, a determinati on of the halogen concentration has usually been combined with some li pid isolation and separation method. This review covers separation by solid phase chromatography, gel permeation chromatography, and liquid- liquid extraction, followed by halogen determination. All studies perf ormed according to this outline have indicated that the major organoha logen compounds are chlorinated fatty acids bound in different lipids. For the detection and identification of individual, halogenated fatty acid methyl esters (FAMEs) liberated from the lipids, gas chromatogra phy (GC) has been employed together with detection methods such as ele ctron capture detection, electrolytic conductivity detection (ELCD), a tomic emission spectrometry, and mass spectrometry. For most environme ntal samples, chlorinated FAMEs must be enriched prior to GC. ELCD is a useful detection method for indicating halogenated FAMEs in the chro matograms, and tentative identification of the halogenated species can be obtained by calculation of retention indices. For closer identific ation of halogenated FAMEs, mass spectrometry (MS) is very useful, in particular when employing the chemical ionisation mode. MS identificat ion, however, is highly facilitated if halogenated species are first i ndicated by element-selective methods.