ONLINE LIQUID-CHROMATOGRAPHY GAS-CHROMATOGRAPHY FOR THE ANALYSIS OF FREE AND ESTERIFIED STEROLS IN VEGETABLE OIL METHYL-ESTERS USED AS DIESEL FUEL SUBSTITUTES

An on-line LC-GC method for the analysis of free and esterified sterols in vegetable oil methyl esters has been set up. Qualitative and quantitative information about this important group of minor components is provided without saponification and off-line pre-separation. Prior to analysis the free sterols are silylated with N-methyl-N-trimethylsilyltrifluoracetamide; betulinol is used as an internal standard. Using concurrent eluent evaporation with the loop-type interface for eluent transfer, transfer temperature and transfer efficiency are carefully optimized. The concentration of the free sterols as well as their qualitative and quantitative composition and the concentration of the sterol esters are determined in five different types of vegetable oil methyl esters. The recovery of the LC-GC procedure and the reproducibility of the quantitative results are evaluated.