This International Standard specifies a gas chromatographic method using capillary columns for the determination of the content of trans fatty acid isomers of vegetable oils and fats. The method is specially designed to evaluate, by a single capillary gas chromatographic (GC) procedure, the level of trans isomers as formed during (high temperature) refining, or during hydrogenation of vegetable oils or fats. The method may also be used to report all other fatty acids (e.g. to obtain the full fatty acid composition and total amounts of saturated fatty acids, mono-unsaturated fatty acids and poly-unsaturated fatty acids) from the same sample and same analysis. NOTE 1 The trans-isomer content as obtained with this method may not agree with the trans-isomer content as obtained using other methods. NOTE 2 During (high temperature) refining (deacidification and deodorization), only geometrical isomers are formed of the mono- and poly-unsaturated fatty acids; i.e. the double bond(s) remain(s) at the same natural position. During hydrogenation, both positional and geometrical isomers are formed. NOTE 3 For some specific cis- and trans-isomers formed during hydrogenation, co-elution is possible. This could influence the accuracy of the result. The level of these isomers is usually negligible in normal partially hydrogenated oils and fats.