This International Standard specifies a method for the determination, in detergents, of anionic-active matter hydrolyzable and non-hydrolyzable under acid conditions. This active matter includes alkyl sulfates and hydroxysulfates and alkylphenol and fatty alcohol ethoxysulfates. The mean relative molecular mass of the two types of active matter must be known or previously determined, if their content is expressed as a percentage by mass. If the detergent contains any oxidizing agent, this must be destroyed before the hydrolysis.