Spectrophotometric determination of anionic surfactants in river waters using 1-(4-nitrobenzyl)-4-(4-diethylaminophenylazo)-pyridinium bromide

Abstract

Nitro, bromo and methyl derivatives of 1-(benzyl)-4-(4-diethylaminophenylazo)pyridinium bromide were synthesised and evaluated as new cationic reagents for the determination of anionic surfactants. These reagents were very stable and reacted with anionic surfactants, such as alkylbenzene-sulphonate and alkylsulphate, to form a 1 : 1 stable ion associate, which was extracted into chlorobenzene in a single extraction. The apparent molar absorptivity of the ion associate of the 4-nitro derivative with sodium di(2-ethylhexyl)sulphosuccinate was 6.10 × 10⁴ l mol^–1 cm^–1(at 573 nm) in chlorobenzene. 1-(4-Nitrobenzyl)-4-(4-diethylaminophenylazo)pyridinium bromide was used in the determination of µg l^–1 levels of anionic surfactants in river water. The results were compared with the methylene blue method (Japanese Industrial Standard method) for river waters. This method is designed to determine anionic surfactant concentrations in solution.