Equivalent chain-lengths of methyl ester derivatives of fatty acids on gas chromatography A reappraisal

Abstract

The equivalent chain-lengths of the methyl ester derivatives of synthetic isomeric unsaturated fatty acids in addition to many from natural sources have been determined by gas chromatography (GC) with modern wall-coated open-tubular columns of fused silica coated with Carbowax 20M TM, Silar 5CP TM, CP-Sil 84 TM and a 5% phenyl-methyl silicone. The complete series of cis-octadecenoates (3- to 17-, but not the 2-), the methylene-interrupted cis,cis-octadecadienoates (3,6- to 14,17- but not the 2,5-isomer) and some cis,cis-octadecadienoates with more than one methylene group between the double bonds (5,12-, 6,12-, 7,12-, 8,12-, 6,10- and 6,11-) were used, together with natural fatty acids from pig testis, rich in the ( n−6) family, and from cod liver oil, rich in the ( n−3) family. There were 79 fatty acids in total. The availability of all these data from a single laboratory at one time allows a reassessment of the value of GC equivalent chain-lengths for the identification of unknown fatty acids, and of stationary phases of particular types for fatty acid analysis in general.