DETERMINATION OF DIACYLGLYCEROL ISOMERS IN VEGETABLE-OILS BY SOLID-PHASE EXTRACTION FOLLOWED BY GAS-CHROMATOGRAPHY ON A POLAR PHASE

Diacylglycerol (DG) isomers in vegetable oils were determined by sever al chromatographic techniques. The use of reversed-phase high-performa nce liquid chromatography on LC-18 under isocratic conditions was inap propriate, since no complete resolution of the 1,2- and 1,3-isomers ap pearing at low retention time was achieved. In addition, overlapping o f some peaks, absence of peaks of the minor components and interferenc es by sterols were observed. On the other hand, the isolation of the p olar fraction by solid-phase extraction (SPE) using a bonded diol phas e and further analysis of the silyl derivatives by capillary GC on 65% -phenyl-methylsilicone, was carried out successfully. No interferences by other components were found and isomerisation by passing the DGs t hrough the SPE column was negligible. The procedure is easy, fast and reproducible, allowing the quantitation and separation of DGs accordin g to their carbon number, their isomeric structure (1,2 and 1,3) and t he degree of unsaturation. The effect of unsaturation on the DG retent ion times depends on the number and arrangement of the double bonds in the molecule. Applications to some vegetable oils are shown.