Photometric determination of cationic surfactants

Abstract

A number of classes of cationic surfactants have been determined by photometric titration with the anionic surfactant sodium dodecyl sulphate. The cationic surfactants were characterised and quantified by high-performance thin-layer chromatography (HPTLC) and, in general, were found to be >75% cationic active matter. The results obtained by photometric titration were within ±6%(relative) of the corresponding results obtained by the two-phase mixed indicator titration procedure that is the current British Standards Institution method (BS 3762: Section 3.4). A photometric approach offers considerable advantages over the two-phase titration. These include a single aqueous phase, a non-operator dependent mode of detection, a reduction of 50% or more in sample analysis time and a greater freedom from interference by non-ionic impurities. The repeatability of the photometric method is similar to that obtained by experienced operators using the two-phase titration.