Extraction and spectrophotometric determination of cobalt in coal fly ashes using 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid

Abstract

The dibromo derivative of 2-(2-pyridylazo)-5-dimethylaminobenzoic acid was synthesised and evaluated as a chromogenic reagent for the determination of trace amounts of cobalt. The reagent was very sensitive and reacted with cobalt(III) to form a 1:2 (Co:reagent) stable green complex, which was extracted into dichloromethane. The apparent molar absorptivity of the cobalt(III) complex was 1.55 × 10⁵ l mol^–1 cm^–1 at 673 nm in dichloromethane. The reagent was used in the determination of trace amounts of cobalt in coal fly ashes and the results were compared with those obtained using the nitroso-R method.