Spectrophotometric determination of trace amounts of vanadium based on itscatalytic 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 catalyt ic effect of the vanadium(V) on the reaction between diphenylamine (DPhA) a nd hydrogen peroxide in a concentrated solution of formic acid. The formati on of the deep-blue oxidation product is followed by a filter spectrophotom eter, equipped with an optical fiber assembly, on line with a PC provided w ith the suitable software. The measurements were taken at 583 nm, with an i mmersed type cell of 1 cm light path length. The optimization of the operat ing conditions regarding concentrations of the reagents, temperature and in terferences are also investigated. The working curve is linear over the con centration range 0.40-4.0 mug/ml vanadium(Ti). The relative standard deviat ion 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-concent ration step. The method was applied to alloys and cosmetics samples. The re sults were compared to those received with a reference method. Good agreeme nt was attained, with a mean error of 0.5%.