o-Tolidine: A new reagent for a simple nephelometric determination of anionic surfactants

Simple light scattering methods (batch, flow injection, sequential injection) for the determination of anionic active matter in detergents based on a novel reaction are reported. The methods are based on formation of a solid phase by association of anionic surfactants and protonated o-tolidine. Measurements were carried out with a conventional spectrofluorimeter at 400 nm, and dodecylbenzene sulfonic acid (DBS) was selected as the reference anionic surfactant. Influence of the main parameters affecting the characteristics of the methods was studied by the univariate method. The optimized methods provided linear ranges from 1.6 to 300 mg l−1 DBS with a repeatability within the 1.2-2.6% range. Reaction time for the manual method is 45 s and sampling frequency for FIA and SIA were estimated as 68 and 20 h−1, respectively. The methods were applied to commercial samples and results successfully compared with a volumetric recommended method. The proposed methods are simple, fast and neither require sample preparation nor any organic solvent.