Sorption-Photometric Determination of Cationic Surfactants with the Use of Silica Gel and Dyes (Zincon and Thiazine Red)

Conditions were determined for the formation of colored ion-pair complexes of cationic surfactants with Zincon and Thiazine Red in aqueous solutions and at the surface of silica gel. A photometric method using Zincon with a detection limit of 1 mg/L and a sorption–spectrometric method using Thiazine Red with a detection limit of 2–3 μg/L were developed for the determination of trace cationic surfactants in water. The relative standard deviations of the results of analysis in both cases were no more than 10%. A test method with the use of indicator tubes filled with silica gel and Zincon as the reagent is proposed; the detection limit of cationic surfactants is 0.5 μg/L (RSD < 25%).