KINETIC - SPECTROPHOTOMETRIC DETERMINATION OF TRACES OF VANADIUM(V) BY ITS CATALYTIC EFFECT ON THE OXIDATION OF 1,4-DIHYDROXYPHTHALIMIDE DIOXIME WITH BROMATE

A kinetic-spectrophotometric method for the determination of trace amounts of vanadium(V) is described. It is based on the catalytic action of this ion on the oxidation of 1,4-dihydroxyphthalimide dioxime by bromate, which yields a red-violet product in acidic medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 500 nm and 30-degrees-C. Using several kinetic methods (tangent, fixed-time and fixed-absorbance), vanadium(V) in the range 10-400 ng ml-1 can be determined. The proposed methods are hardly subject to interferences. The tangent method was used for the determination of vanadium in atmospheric particulate matter, human serum and synthetic mixtures. The kinetic parameters of the catalysed and uncatalysed reactions are reported.