Determination of cholesteryl esters and of cholesteryl and epicholesteryl silyl ethers by capillary gas chromatography

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Abstract
The capillary gas chromatography of cholesteryl esters after splitless injection into a 25-m, OV-1-coated, fused silica WCOT column and a 7-m Silar 10C-coated glass WCOT column is reported. The nonpolar OV-1 column separated the cholesteryl esters principally on the basis of carbon number, but separation of the saturated esters from the unsaturated esters was also achieved. The polar Silar 10C column separated the esters mainly according to the degree of unsaturation. Thus, the 2 column types complement each other in the analysis of nanogram quantities of cholesteryl esters from small samples, such as those from plasma or single arterial atherosclerosis lesions. This technique therefore obviates some of the difficulties of analyzing such cholesteryl ester samples in the form of methyl esters (incomplete transmethylation, and contamination by solvent impurities and/or plasticizer esters). Both columns were also found to be useful for the separation and quantitaiton of thet-BDMS ethers of cholesterol and epicholesterol in mixtures containing various proportions of these epimers.