Spectrophotometric determination of thallium after its extraction as an ion-pair of the chloro-complex and pyronine G

A sensitive and selective procedure for the spectrophotometric determination of thallium is described. The method is based on the formation of an ion-pair between TlCl(4)](-) and the pyronine G cation in chloride-containing acid media. The ion-pair is extracted into benzene and permits the determination of as low as 0.3 mug of thallium in a final volume of 25 ml at 530 nm. The system obeys Beer's law in the concentration range 1-14 mug of thallium in a final volume of 25 ml. Potassium iodate was found to be highly effective for the oxidation of Tl(I) to Tl(III) and the presence of excess oxidant does not interfere. The method can be used for the determination of thallium in high purity cadmium, cadmium sponge and rock samples.