The document specifies a method for the determination of up to approximately 1,5 milli-equivalents of tertiary amine oxide. Components which lose the basicity in reaction with acetic anhydride by forming an amide (e.g. primary and secondary amines) interfere. If present, these primary and secondary amines must be determined by a different procedure e.g. reaction with carbondisulfide. This method is applicable to solids or to aqueous solutions of the active material. The molecular mass of the amine oxide shall be known if its content is expressed as a percentage of mass.