Methyl esters are still the most popular derivative for the gas chromatography (GC) of fatty acids. When analyzing triglycerides and other liquids for fatty acid composition, methyl esters usually are made by a saponification-acidic methanolysis technique. Transesterification with sodium methoxide is also often used for preparing methyl esters. However, there are some drawbacks to both these procedures: the saponification-esterification method requires an extraction step which can be troublesome, and the sodium methoxide transesterification technique does not convert any free fatty acids present to esters. A technique has been developed which overcomes these disadvantages. Tetramethylammonium hydroxide in methanol (TMAH) is used to catalyze the transesterification of the fat dissolved in diethyl ether, and methyl esters form almost instantly. Glycerine drops out of solution to form a second layer containing the bulk of any free fatty acids present as their TMAH soaps. GC of the ether layer gives the fatty acid composition of the glycerides. On injecting the lower layer, the TMAH soaps pyrolyze to form methyl esters. If methanol is added to the flask to solubilize the glycerine and excess base neutralized with methanolic HCI, total fatty acid composition can be obtained by chromatographing the resulting solution.