KINETIC-SPECTROPHOTOMETRIC DETERMINATION OF TRACES OF OSMIUM BY ITS CATALYTIC EFFECT ON THE OXIDATION OF PYROGALLOL RED BY HYDROGEN-PEROXIDE

A Kinetic-spectrophotometric method for the determination of ultra-tra ce amounts of osmium(VIII) is described. It is based on the catalytic action of osmium(VIII) on the oxidation of Pyrogallol red with hydroge n peroxide , yielding a colorless product in neutral medium. The react ion is followed spectrophotometrically by measuring the rate of change in absorbance at 540 nm and 30-degrees-C. Os(VIII) in the range 0.005 -100 ng.ml-1 can be determined. The proposed method is hardly subject to interferences. The relative standard deviation is 1.5% for 1 ng.ml -1 of Os(VIII). The kinetic parameters of the catalyzed and uncatalyze d reactions are reported. The detection limit is 1 pg.ml-1.