A transparent membrane filter for the solid-phase spectrophotometric determination of trace cationic surfactant in water

Abstract

The use of a transparent membrane filter is proposed for a simple and rapid solid-phase spectrophotometric determination of trace cationic surfactant in water. Cationic surfactant is retained on the membrane filter during filtration as an ion-pair with an intensely colored inert anionic cobalt complex, bis[4-hydroxy-3-(8-quinolyl)azo-1-naphthalenesulfonato]cobaltate(III). The absorbance of the colored membrane filter is measured directly at 593 nm against a reagent blank. A linear calibration was obtained for 0.8–4.0 × 10^–6 mol dm^–3 of benzyldimethyltetradecylammonium ion as a standard material. Inorganic major ions in natural water at mg dm^–3 or higher concentrations and sodium dodecylsulfate at 0.4 mg dm^–3 did not interfere with the determination. The recoveries of the cationic surfactant added to river water and tap water were quantitative.