Catalytic spectrofluorimetric determination of vanadium using oxidation of o-phenylenediamine with bromate in the presence of gallic acid

Abstract

A highly sensitive method for the determination of vanadium was developed by spectrofluorimetric monitoring (λ_ex= 415 nm; λ_em= 555 nm) of the vanadium-catalysed oxidation of o-phenylenediamine with bromate in the presence of gallic acid as an activator. Kinetic studies suggested that the complexation of vanadium with gallic acid accelerated the catalysed reaction markedly. The fluorescence intensity (I) increased linearly with increasing reaction time (t) in the initial reaction at pH 4.0 (acetate buffer) and 25 °C. The calibration graph had a linear range of 0–0.8 µg l^–1 for both V^V and V^IV and was constructed by using the reaction rate, i.e., the slope of the I versus t graph. The detection limit was 2 ng l^–1. The interferences from iron ions and humic acid were checked by simple visual and spectrofluorimetric detection and eliminated by dilution of the sample solutions. The proposed method was successfully applied to the determination of vanadium down to 0.02 µg l^–1 in river-, rain- and tap water.