Silver ion solid‐phase extraction chromatography for the analysis of trans fatty acids

Abstract

Summary This article describes the application of silver ion solid-phase extraction (Ag + -SPE) to the separation of the fatty acid methyl esters (FAMEs)prepared from a partially hydrogenated fish oil (PHFO) with a trans fatty acid (FA) content of 41%. The complex FAME mixture wasresolved into the following FAME fractions: saturated FA, trans-monounsaturated FA (trans-MUFA), cis-MUFA, and several polyunsatu-rated FA (PUFA) fractions with mixed geometric and positional isomers. Fractions were analyzed by gas chromatography (GC) using a 100 mcyanopropyl polysiloxane (CPS) coated capillary column. The GC analysis of the Ag + -SPE fractions allowed for the identification of the trans-andcis-MUFAandotherFAMEpreparedfromPHFO. Introduction As early as 1966 Morris [1] had concluded that argentation chroma-tography was third in importance to GC and thin-layer chromato-graphy (TLC) for the analysis of lipids. This optimistic predictionwas largely based on separations achieved by using Ag + -TLC toresolve FAMEs with different numbers and geometric configura-tions of double bonds. These results were essential to complementGC separations of FAMEs on packed columns that provided reso-lution determined by chain length and number of double bonds, butcould not resolve geometric isomers. One might have thought thatthe subsequent development of the very long, highly polar GC ca-pillary columns that now make it possible to resolve most geo-metric and positional isomers and PUFAs would have phased outthe need for silver ion (Ag