Dual-wavelength β-correction spectrophotometry for directly determining anionic detergents in environmental water

Abstract

Trace amounts of anionic detergents in environmental water have been determined directly by dual-wavelength β-correction spectrophotometry with ethyl violet (EV) at pH 2. The extraction of anionic detergents with nitrogen gas is effective for preconcentrating trace anionic detergents and separating other ions. The dual-wavelength β-correction method can eliminate completely the effect of excess EV to give the real absorbance of the product formed. Therefore, the composition ratio of the product can be calculated. The results show that Beer's law is obeyed over the concentration range 0–5.0 mg l^–1 for anionic detergents, the composition of the colouring product formed by the anionic detergent with EV is 1:1 and the detection limit for anionic detergents is 0.01 mg l^–1.