The substance is determined in a medium consisting of an aqueous and a chloroform phase by titration with a standard volumetric cationic-active solution (benzethonium- chloride) in the presence of an indicator which consists of a mixture of cationic dye (dimidium bromide) and an anionic dye (acid blue 1). The method is applicable to solids or to aqueous solutions of the active material. The relative molecular mass of the anionic active matter has to be known. The method is not applicable if cationic surface active agents are present.