This European Standard specifies a method for the determination of the content of inorganic sulphate in anionic surface active agents. It can be applied to a-olefin sulphonates and n-olefin sulphonates, alcohol sulphates, alcohol ether sulphates, alkyl benzene sulphonates and other alkyl sulphonates. This method is used also for the determination of inorganic sulphate in alkyl benzene sulphonates or other alkyl sulphonates in their acid form. This method also applies to deep-coloured samples.