Determination of thallium in bismuth by differential pulse anodic-stripping voltammetry without preliminary separation

The determination of trace levels of thallium in bismuth and bismuth salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent, in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte in the absence of surfactant, bismuth at concentrations below 10(-4)M does not interfere. When the electrolyte also contains tetrabutylammonium ions at 0.01 M concentration, bismuth can be tolerated at concentrations up 0.05M, and the height of the thallium peak is unaffected. It is thus possible to determine 1 nM Tl(I) in the presence of 0.05M Bi(III), i.e., Tl at the 1 x 10(-6)% level in bismuth. The precision of the determination and the recovery are satisfactory. Neither an 800-fold ratio of Cu(II) nor a 10(7)-fold ratio of Pb(II) to Tl(I) interferes in the determination. Other cations such as Zn(2+), Cd(2+), In(3+), Hg(2+), Fe(3+), Sb(3+) and Sn(4+) in 10(4)-fold molar ratio to Tl(I) have no effect on the determination. Thallium has been determined in bismuth metal and in bismuth nitrate of various degrees of purity.