Spectrophotometric determination of cationic surfactants in water with an anionic dye-Disulphine Blue

Abstract

After removal of anionic surfactants by an ion-exchange technique, cationic surfactants were extracted as their chlorides into chloroform. Ion pairs of the cationic surfactants and Disulphine Blue formed in the chloroform phase were measured spectrophotometrically as follows : A 50 ml of a sample solution containing cationic surfactants (above 1 \\g as Zephiramine) is passed through an anion-exchange column (Amberlite IRA-401, 15 ml) at a rate of 1 ml/min and the column is washed with 50 ml of 50% methanol. Five milliliters of sodium chloride solution (10%) and 10 ml of chloroform are added to the eluate. The mixture is then shaken for 1 min to extract cationic surfactants into chloroform. The chloroform phase is shaken for 1 min with a mixture of 10 ml of citrate buffer solution (0.1 M, pH 5), 5 ml of sodium sulfate solution (0.4 M) and 1.5 ml of Disulphine Blue solution (1.17 × 10-4 M). The absorbance of the chloroform phase is measured at 628 nm. Cationic surfactants in water above 20 μg/1 could be determined by the proposed method. © 1990, The Japan Society for Analytical Chemistry. All rights reserved.