CONTINUOUS SOLVENT-EXTRACTION METHOD FOR THE SPECTROPHOTOMETRIC DETERMINATION OF CATIONIC SURFACTANTS

A rapid and automated spectrophotometric method for the determination of cationic surfactants, using the AutoAnalyzer, has been developed. This method is based on the continuous solvent extraction of the ion-pair complex formed in the reaction of Orange II with a cationic surfactant. Good traces and identical molar responses were obtained with seven different types of surfactant using methanol in the Orange II reagent. Fatty amines in mixtures of the amines and quaternary ammonium surfactants were determined by changing the pH of the aqueous phase. The proposed method was applied to the determination of cationic surfactants in several commercial products. The results agreed with those obtained by the two-phase titration procedure. The detection limit is 5 μM and the capacity is 10-20 samples per hour, with a relative precision of better than 1.5%.