ANALYSIS OF MIXTURES CONTAINING FREE FATTY-ACIDS AND MONOGLYCERIDE, DIGLYCERIDE AND TRIGLYCERIDE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY COUPLED WITH EVAPORATIVE LIGHT-SCATTERING DETECTION

Commercial monostearates of glycerol, generally used as antistatic age nts for thermoplastic polymers, consist of a complex mixture of mono-, di- and trisubstituted glycerides and the corresponding fatty acids. Thus far, the glycerides and the fatty acids have been analyzed separa tely by high-performance liquid chromatography (HPLC). In fact, the si multaneous analysis of glycerides and fatty acids requires esterificat ion of the acids in order to avoid overlapping of the chromatographic peaks. This paper describes an HPLC method which allows the direct sep aration and identification, simultaneously and in a single run, of the variously substituted glycerides, and also the corresponding saturate d fatty acids that are found as by-products in commercial glycerol mon ostearates. The procedure is based on the use of a ternary gradient HP LC instrument equipped with an evaporative light-scattering detector; the stationary phase was a reversed-phase RP-8 end-capped (Merck) colu mn; the mobile phase was two consecutive binary gradients consisting o f acetonitile-water plus acetic acid (0.1%, v/v) and acetonitrile-meth ylene chloride. The method is fast and shows high sensitivity and sele ctivity, being able to separate also the positional isomers of mono- a nd diglycerides in addition to the mixed di- and triglycerides.