DETERMINATION OF ANIONIC SURFACTANTS IN AN AQUEOUS-MEDIUM BY DIFFERENTIAL PHOTOMETRIC TITRATION METHOD

A simple and rapid automatic photometric titration method was develope d for the determination of anionic surfactants in a one-phase aqueous system with tetrabromophenolphthalein ethyl ester (TBPE) as an indicat or. In the presence of non-ionic surfactants such as Triton X-100, pro tonated TBPE reacts with cation (Q+) to form an ion associate (Q+.TBPE -), causing a color change from yellow to blue. The titrant, distearyl dimethylammonium ion, was added to an anionic surfactant solution at p H 3.2, and the absorbance changes were monitored by a fiber-optic sens or with a 630 nm interference filter. The end points were read from th e inflection points with differential curves. Anionic surfactants at c oncentrations from 10(-6) approximately 10(-3) mol dm-3 could be deter mined by the proposed, method. The relative standard deviations of var ious anionic surfactants were 0.3 approximately 0.4%. The proposed met hod was applied to some practical samples, and the results, except for those of anionic surfactants possessing polyoxyethylenyl groups, were in good agreement with the results of the JIS titration method (Epton method) and a solvent extraction method with Ethyl Violet.