Separation of cholesterol esters by silver ion chromatography using high-performance liquid chromatography or solid-phase extraction columns packed with a bonded sulphonic acid phase

Abstract

Two methods for the separation of cholesterol esters, based on the number of double bonds in their fatty acid moieties, are presented. Silver ion chromatography, usually performed on thin-layer chromatographic plates, was made suitable for high-performance liquid chromatography (HPLC) and solid-phase extraction. Separation on a bonded sulphonic acid phase loaded with silver ions was achieved with cholesterol esters containing up to six double bonds in their fatty acid moieties. No cross-contamination between fractions with different numbers of double bonds was detected with the HPLC method, as was demonstrated by subsequent gas chromatographic analysis of the fatty acid moieties, following transmethylation. For adequate separations with the solid-phase extraction columns it proved important to avoid over-loading. The methods may be of use for the off-line analyses of the sterol compositions of the isolated fractions, which each contain sterol esters with an equal number of double bonds in their fatty acid moieties.