Limitations of ambient temperature methods for the methanolysis of triacylglycerols in the analysis of fatty acid methyl esters with high accuracy and reliability

A comparison is presented of a method for the preparation of fatty acid methyl esters, involving hydroxide catalyzed transesterification at ambient temperature, with a second method employing methoxide catalyzed transesterification at reflux temperature. The first of these methods was specifically designed for the analysis of fats that contain very short chain length fatty acids (butyric and caproic acids), but it has been suggested that it might be suitable as a general method for the preparation of esters. It is now shown that the methoxide/reflux method gives more accurate results than does the hydroxide/ambient method when the samples to be analyzed contain high levels of long chain length fatty acids (e.g. stearic, palmitic, elaidic, oleic) and that it is quicker and at least as simple to carry out. The hydroxide/ambient method should be used only for its specific purpose and, when used, the procedure should be strictly followed and carefully standardized. Results obtained from fats that contain significant quantities of long chain length components should be viewed with suspicion.