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.