EVALUATION AND IMPROVEMENT OF TRANSESTERIFICATION METHODS OF TRIGLYCERIDES

The causes responsible for the low reproducibility of the gas chromato graphic method used to analyze fatty acid methyl esters, derived from the transesterification of triglycerides in n-hexane by means of metha nol potassium hydroxide, were identified and eliminated. Partition coe fficients (Kd) of short-chain fatty acid methyl esters between n-hexan e and methanol were determined. These results indicate that even under the best experimental conditions, a substantial portion of these comp ounds are transferred in the methanol phase and therefore are not anal yzed. Accurate results, to within 2% were obtained by rigorously contr olling the volume of the reagents and introducing appropriate correcti on factors. The accuracy of the results, reported as a percentage by w eight, did not depend on the completeness of the transesterification r eaction. In the analysis of fatty acids as butyl eaters, a measurable quantity of butyric ester was lost during the washing phase with water . By contract, butyric acid pentyl ester is insoluble in water. Theref ore we propose an accurate method to analyze fatty acids as pentyl est ers. Oleic and elaidinic acids derived from triglyceride transesterifi cation are easier to separate as methyl esters than as longer butyl or pentyl esters.