CAPILLARY GAS-LIQUID-CHROMATOGRAPHY OF ACETATE-METHYL ESTERS OF BILE-ACIDS

Gas-liquid chromatographic separations of acetate-methyl eaters of sev eral common bile acids with and without a hydroxyl group at C-6 are co mpared with those of the corresponding trimethylsilyl ether-methyl eat ers on a CP-Sil-5 CB capillary column. Unlike the trimethylsilyl ether derivatives, the retention indices of the corresponding acetates were greatly influenced by the number of hydroxyl groups in the ring syste m. Epimeric hydroxyl groups at carbons 6, 7 as well as 12 increased re tention index of the acetate-methyl esters of the bile acids, the effe ct of the 7 beta-hydroxyl group being most prominent. The 6 beta-aceto xyl group increased the retention index more than the 6 alpha-acetoxy group and contrary to the trimethylsilyl ether derivatives, a 6 beta,7 beta-diacetoxy group showed larger increase in the retention index th an the corresponding 6 alpha,7 beta-diacetoxy group. The acetate deriv atives of bile acid-methyl eaters show larger retention times and redu ced sensitivity than the corresponding trimethylsilyl ether derivative s. However, gas chromatography of bile acid acetate-methyl esters can be very useful for the characterization of bile acids and for bile aci d analysis in the rat where muricholic acids and hyodeoxycholic acid a re in abundance, since these bile acids are difficult to resolve from each other and from other common bile acids as the trimethylsilyl ethe r derivatives.