Spectrophotometric determination of trace amounts of vanadium based on its catalytic effect on the reaction of diphenylamine and hydrogen peroxide

In this work a kinetic spectrophotometric method for,I the determination of trace amounts of vanadium is presented. The method is based on the catalytic effect of the vanadium(V) on the reaction between diphenylamine (DPhA) and hydrogen peroxide in a concentrated solution of formic acid. The formation of the deep-blue oxidation product is followed by a filter spectrophotometer, equipped with an optical fiber assembly, on line with a PC provided with the suitable software. The measurements were taken at 583 nm, with an immersed type cell of 1 cm light path length. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The working curve is linear over the concentration range 0.40-4.0 mug/ml vanadium(Ti). The relative standard deviation for a standard solution of 0.6 mug/ml of vanadium is 0.5% (n = 5). The proposed method proved highly sensitive, selective and relatively rapid for the assay of vanadium, at low level of 0.40 mug/ml without any pre-concentration step. The method was applied to alloys and cosmetics samples. The results were compared to those received with a reference method. Good agreement was attained, with a mean error of 0.5%.