Spot Test and Spectrophotometric Determination of Anionic Surfactants on Paper Impregnated with Mixed Hydro xide of Aluminum and Zinc

Abstract

A rapid and simple detection method for anionic surfactants is proposed.A 200-μl portion of test solution adjusted at pH 4-6 is dropped onto the filter paper impregnated with equimolar mixture of zinc and aluminum hydroxides. After being dried, the paper is moistened with water. Dodecylbenzenesulfonate (DBS) is detected as a white spot. The identification limit is 1 μg. When a drop of ethanol and a drop of Rhodamin B solution adjusted at pH 5.5 are added to the white spot, a reddish violet spot is obtained. The identification limit for DBS is 0.2 μg. For the spectrophotometric determination, the reddish violet spot is washed with water to remove excessive Rhodamine B and extracted with ethanol. The absorbance of the extract is measured at 545 nm. DBS ranging from 5 to 100 ppm can be determined. Cationic, nonionic and amphoteric surfactants do not interfer with the determination of anionic surfactants,