KINETIC-SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF SELENIUMWITH CATALYTIC REDUCTION OF GALLOCYANINE BY SULFIDE

A kinetic-spectrophotometric method is presented for the determination of trace amounts of selenium (0.010 - 0.500 mg.ml(-1)), based on the catalytic effect of Se(IV) on the reduction of Gallocyanine by sodium sulfide, which yields a colorless product. The reaction is followed sp ectrophotometrically by measuring the absorbance change at 620 nm and 30 degrees C. The detection limit is 0.002 mu g.ml(-1). Se(VI) can be reduced with hot hydrochloric acid to Se(IV), allowing determination o f total selenium. The variables which affected the reaction rate were fully investigated and the optimum conditions were established. The re lative standard deviation for 50 ng.ml(-1) of selenium was 2.5% (n=6). The method was applied to determination of Se(IV) in real samples.