Photometric determination of cationic surfactants in aqueous solutions using methylene blue and silica gel

The method is based on the coadsorption of surfactants and Methylene Blue under batch conditions. It was found that the color intensity of the Methylene Blue solution determined photometrically is proportional to the amount of the adsorbed surfactant. It is proposed to use silica gel as an adsorbent in the determination of cationic surfactants. The concentration of surfactants is determined using a calibration plot. This method is suitable for the determination of 0.002-1 g/L of quaternary ammonium compounds and amine salts. The relative error of the determination is 6-12%. The detection Limit for technical surfactants under study is 0.4-8 mg/L.