Spectrophotometric determination of anionic surfactants with 1-(4-bromomethylbenzyl)-4-(4-diethylaminophenylazo)-pyridinium bromide.

Abstract

A new cationic dye, 1-(4-bromomethylbenzy1)-4-(4-diethylaminophenylazo)-pyridinium bromide, with anionic surfactants such as laurylbenzenesulfonate(LBS) and laurylsulfate (LS), reacts to form ion-associates extractable into benzene. The concentration of the surfactants can be determined by measuring the absorbance of extracts at 545 nm. Calibration curve obeyed Beer's law over the range 0.222.2×10-5mol dm-3 (in benzene) of the surfactans. The apparent molar absorptivity of the ion-associates is 34000 dm3 mol-1 cm-1. The procedure for surfactant determination is as follows : In a 30 ml stoppered test tube, place 25 ml of sample solution, 1 ml of 4.9×10-4 mol dm-3 reagent and 1 ml of phosphate buffer solution (pH 7). Add 5 ml of benzene, and shake the test tube for 5 min mechanically and allow to stand for 15 min. Measure the absorbance of the benzene phase at 545 nm with glass cells of 1-cm path-length. The relative standard deviation for 1.1×10-6 mol dm-3 LBS was 3.4%.