This International Standard specifies a procedure for the determination of alkyl nitrate in diesel fuel in the concentration range 0,03 % (V/V) to 0,30 % (V/V) (volume fraction 0,03 % to 0,30 %). A knowledge of the specific alkyl nitrate present in the diesel fuel is required for accurate determinations, as the calibration of instrumentation is reliant on reference solutions containing the nitrate to be analysed. When the specific alkyl nitrate is not known, a result comparative to a reference alkyl nitrate (4.2) gives indicative information. NOTE — The addition of certain alkyl nitrates to diesel fuel enhances the cetane number as measured by the engine test described in ISO 5165. It has no effect on the cetane index value as described in ISO 4264. See annex A. The presence of nitrate esters, inorganic nitrate ions and nitrogen oxides will interfere with this determination.