This part of ISO 12966 gives an overview of the gas chromatographic determination of fatty acids, free and bound, in animal and vegetable fats and oils following their conversion to fatty acid methyl esters (FAMEs).The qualitative and quantitative determination of the composition of fatty acids by gas liquid chromatography (GLC) is a widely used application in lipid analysis. It is used for the characterization of fats and oils, or fatty foodstuffs after the extraction of the oil from the matrix. The bound fatty acids of the triacylglycerols (TAGs) and, depending on the esterification method, the free fatty acids (FFA) and other lipids, are converted to fatty acid methyl esters (FAMEs), which are determined by capillary gas chromatography. Depending on the number of different fatty acids (theoretically more than 50 different fatty acids can be present) capillary columns with a length of 10 m to 100 m are used for a separation.The GLC of FAMEs is applicable to all natural and synthetic mixtures of tri-, di- and monoacylglycerols, to fatty acid esters, free fatty acids, soaps and other fatty compounds. With this suite of standards, FAMEs from C4 to C26 can be determined, including saturated fatty acid methyl esters, cis- and trans-monounsaturated fatty acid methyl esters, and cis- and trans-polyunsaturated fatty acid methyl esters.For the determination of short chain fatty acids, isopropyl and butyl esters are often used so as to avoid interferences with the solvent peak and in order to reduce differences in detector responses.