Capillary electrochromatography of sterols and related steryl esters derived from vegetable oils

Capillary electrochromatographic (CEC) separations of plant sterols and related esters were evaluated under various conditions. Stationary phases included octadecylsilica (C18) and triacontylsilica (C30). Mobile phases comprised acetonitrile, tetrahydrofuran, and tris(hydroxymethyl) aminomethane buffers in aqueous or non-aqueous systems. Apart from notable differences in component resolution, both C18 and C30 phases had dramatic influence on the elution behavior of the title compounds. Generally, C18 had greater selectivity for most components with elution patterns in consistence with the hydrophobicity of side chain structures, while no predictable trend of analyte elution was observed in CEC with C30. In the latter column systems, analyte separations appeared to be improved by conversion to benzoates or ferulates. Twenty-four-epimers of campesterol acetate and 7-campestenol acetate as well as the campesterol–stigmasterol pair were readily resolved by CEC with either phase. However, the cholesterol–stigmasterol pair was barely resolved and had an elution order opposite to that of their acetates or benzoates. Potential applicability of the CEC technique in the analysis of sterols and sterol ferulates in vegetable oil is demonstrated.