HIGHLY SENSITIVE KINETIC SPECTROPHOTOMETRIC METHOD FOR THE DETERMINATION OF OSMIUM BY ITS CATALYTIC EFFECT ON THE OXIDATION OF GALLOCYANINE BY HYDROGEN-PEROXIDE

A method is presented for the determination of osmium as osmium tetroxide (10-60000 pg.ml(-1)), based on catalytic effect of Os(Vm) on the oxidation reaction of gallocyanine by hydrogen peroxide. The reaction is monitored spectrophotometrically by measuring the decreasing colour of gallocyanine at 625 nm by the fixed time method. At a given time of 4.0 min at 25 degrees C, the detection limit is 1 pg.ml(-1) and the relative standard deviation for 150 pg.ml(-1) osmium is 1.5% (n=10). The method is free from most interferences, especially from large amounts of platinum metals. The procedure has been successfully applied to the determination of ultra trace amounts of Os(VIII) in synthetic samples and ore sample without preconcentration.