This International Standard specifies methods of preparing the methyl esters of fatty acids. It includes methods for preparing fatty acid methyl esters from animal and vegetable fats and oils, fatty acids and soaps. To cover different requirements, three methylation methods are specified, as follows: a) boron trifluoride (BF3) method (see clause 3); b) trimethylsulfonium hydroxide (TMSH) method (see clause 4); c) trans-esterification method (see clause 5). Methyl esters so produced are used in various analytical procedures requiring such derivatives, for example gasliquid chromatography (GLC), thin-layer chromatography (TLC) and infrared spectrometry (IR).