Identification of fatty acid methyl esters as minor components of fish oil by multidimensional GC‐MSD: New furan fatty acids

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Abstract
The separation and analysis of furan fatty acids and other minor component fatty acids present at very low concentrations in complex sample matrices, such as fish oil or lipids derived from liver and testes, require several pre‐analytical separation steps if single column gas chromatography is to furnish sufficient resolution: after extraction and transesterification hydrogenation, urea complex precipitation and argentation TLC have been applied prior to GC analysis of furan fatty acids.By using multidimensional GC‐MSD with cooled injection and flow‐controlled column switching with intermediate cold trapping, it has been possible to identify directly the methyl esters of furan fatty acids without further pre‐analytical separation.The most common of the furan fatty acids can be subdivided into two groups depending on whether they bear a propyl or pentyl side group in the 5‐position of the furan ring. In addition to the eight furan fatty acids known to be present in fish oil, six new ones were identified, four with propyl substitution and two with pentyl substitution. Four have earlier been reported to be present in the hepatopancreas of crayfish and in fish tissue, whereas the propyl‐substituted 16,19‐epoxy‐17,18‐dimethyldocosa‐16,18‐dienoic acid and the pentyl‐substituted furan fatty acid 6,9‐epoxy‐7‐methyltetradeca‐6,8‐dienoic acid were hitherto unknown.