Differential titrimetric determination of mixtures of selenium and tellurium

Methods are described for the differential titrimetric determination at room temperature of mixtures of selenium(IV) and tellurium(IV). The test solution in 0.75-3.5M condensed phosphoric acid medium is oxidized with an excess of permanganate and the unreacted permanganate is titrated with iron(n), with ferroin as indicator, to indicate the total content of selenium and tellurium present. Then 10-20 ml of 10M sulphuric acid, 0.4 ml of 0.1% osmium tetroxide solution and an excess of arsenic(III) are added to the same solution and the unreacted arsenic(III) is titrated with permanganate (ferroin as indicator) to indicate the content of tellurium.