The use of 204thallous chromate columns for the determination of lead

0.5-10 micromoles of lead in aqueous solution may be determined by passing the solution through a short column of thallous chromate labelled with 204Tl displacement method and counting the eluate. Cations giving very insoluble chromates like Ba2+ interfere and the technique is not suitable for solutions with pH<5.5. Consideration of solubility product data as well as the ionic sizes shows that both Ba2+ and Pb2+ should replace thallium ions from thallous chromate. The experiments were carried out by precipitating Ba2+ and Pb2+ present in the mixture as sulphates and then treating the sulphates with an excess of ammonium acetate to dissolve lead sulphate as acetato complex of lead. It was observed that up to the molar ratio of Ba to Pb 0.1, the interference was almost negligible. The influence of several other cations like Al3+, Ni2+, Co2+, Mg2+, Ca2+, Zn2+, Fe2+ and Fe3+ was studied, out of which Fe2++Fe3+ were found to interfere even in the presence of masking agents. However, a preliminary extraction with ether saturated with 6M HCl was found to remove Fe3+ completely from the solution. From the solubility product data it is clear that Ag+, Ca2+, Sr2+, Cu2+, Hg22+ do not interfere. (T.I.)