This International Standard specifies a spectrometric method for the determination of the permanganate absorption number of caprolactam for industrial use. The permanganate absorption number is a measure of the oxidizable impurities in caprolactam, determined in a buffered neutral aqueous medium under fixed conditions. The method is applicable to purified caprolactam (and intermediates in the caprolactam purification process) with an alkalinity or acidity lower than 0,50 mmol/kg and a PAN value of up to 35.