ANALYSIS OF FATTY-ACID MONOACYLGLYCEROL AND DIACYLGLYCEROL POSITIONALISOMERS BY SILVER ION HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Mono- and diacylglycerol positional isomer pairs were separated (as ac etates) by silver ion high-performance liquid chromatography on a comm ercially available column using an isocratic solvent system of 1.2% (v /v) acetonitrile in hexane and flame ionization detection. The acetate derivative(s) from the 1- and 2-monoacylglycerols and 1,2- and 1,3-di acylglycerols were prepared by acetic anhydride-pyridine. Conversion o f the thermodynamically less stable 2-mono- and 1,2- diacylglycerols t o triacylglycerols containing acetate(s) in the 1-, 3- and 2-positions , respectively, resulted in <3% isomerization. Conversion of the therm odynamically more stable 1-mono- and 1,3-diacylglycerol analogues yiel ded <1% isomers. Less than 0.5% inter-esterification by-products were noted. The triacylglycerol, the diacylglycerol-monoacetate isomer pair , the monoacylglycerol-diacetate isomer pair and triacetin were comple tely separated for the 16:0 and 18:1 fatty acid series. The triacylgly cerols eluted first and the triacetin eluted last. The 16:0 elution pa ttern is unusual, since silver ion chromatographic separations are gen erally ascribed to the interaction of silver ions with carbon-carbon d ouble bond pi-electrons, a condition absent in the 16:0 series.