This International Standard specifies a method for the accurate determination of isolated trans bonds in natural or processed long-chain fatty acids, fatty acid esters and triglycerides with trans isomer levels > 5 %. The method is not applicable, or is applicable only with specific precautions, to — fats and oils containing high levels (over 5 %) of conjugated unsaturation (e.g. tung oil), — materials containing functional groups which modify the intensity of the C-H deformation about the trans double bond [e.g. castor oil containing ricinoleic acid or its geometrical isomer, ricinelaidic acid (12-hydroxy-9-octadecenoic acid)], — mixed triglycerides having long- and short-chain moieties (such as diacetostearin), or in general, — any materials containing constituents which have functional groups which give rise to specific absorption bands at or sufficiently close to interfere with the 966 cm band of the C-H deformation of the isolated trans double bond. NOTE Dienes, such as cis-trans and trans-trans dienes, can affect the calibration. For accurate determinations on materials with trans levels below 5 %, a standardized capillary GLC method is recommended (for example, see ISO 15304).