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Abstract
The causes responsible for the low reproducibility of the gas chromatographic method used to analyze fatty acid methyl esters, derived from the transesterification of triglycerides in n-hexane by means of methanol potassium hydroxide, were identified and eliminated.
Partition coefficients (Kd) of short-chain fatty acid methyl esters between n-hexane and methanol were determined. These results indicate that even under the best experimental conditions, a substantial portion of these compounds are transferred in the methanol phase and therefore are not analyzed. Accurate results, to within 2%, were obtained by rigorously controlling the volume of the reagents and introducing appropriate correction factors.
The accuracy of the results, reported as a percentage by weight, did not depend on the completeness of the transesterification reaction.
In the analysis of fatty acids as butyl esters, a measurable quantity of butyric ester was lost during the washing phase with water. By contract, butyric acid pentyl ester is insoluble in water. Therefore we propose an accurate method to analyze fatty acids as pentyl esters.
Oleic and elaidinic acids derived from triglyceride transesterification are easier to separate as methyl esters than as longer butyl or pentyl esters.