Separation of tissue cholesterol esters and triglycerides by silicic acid chromatography.

bUnequivocal class separations of tissue lipids are important particularly whcn high temperature gas Chromatography is used at the same time for the determination of the long-chain acid composition of major lipid classes. This problem was studied most recently by Hirsch and Ahrens (1) ; their procedurc involves silicic acid column chromatography with clution by ether-petroleum ether mixtures for ((neutral” lipids, and methanol for phospholipids. The separation of cholesterol esters from triglycerides is difficult to achieve ; the Hirsch-Ahrens scparation procedure is the most detailed and most effective one that has been described. Benzene-hexane (and benzene-petroleuni ether) mixtures applied to a silicic acid column can usually be made to give the same kind of results as cther-petroleum ether mixtures, and Borgstr6m’s method (2) for class separations was based on the use of the former solvent pair. I n these procedures and that of Lipsky e t al. (3) , as in the ether-petroleum ether methods of Fillerup and Mead (4) and Luddy e t al. (5), the key to successful duplication of separations lies in the preparation of the silicic acid. Since benzene-hexane mixtures are more convenient to use than ethcr-petroleum ether mixtures, the following method was developed for this solvent pair ; the relatively large changes in benzene concentration make the neutral lipid separations particularly easy to accomplish.