SUB-STOICHIOMETRIC ISOTOPE-DILUTION ANALYSIS FOR THE DETERMINATION OF THALLIUM BY LIQUID SCINTILLATION-COUNTING

A sensitive and selective sub-stoichiometric isotope dilution method for the determination of trace amounts of thallium is described. The method is based on the extraction of the ion-association complex with a sub-stoichiometric amount of Victoria Blue B into toluene from 0.5 mol l-1 HCl. The beta activity of thallium-204 was measured by liquid scintillation counting. The counting efficiency was found to be 95%. The calibration graph was linear in the range 0-4 mug of Tl(III) in a final volume of 30 ml. The method is sensitive down to 0.2 mug of Tl(III) in a final volume of 30 ml. The interferences of Hg(II), Sb(III), As(III) and Mo(VI) were overcome by collecting thallium on PbS. The method was found to be useful for the determination of thallium in flue dust, zinc ore, zinc base die castings, rock samples, cadmium turnings and cabbage leaf samples.