ANODIC-STRIPPING VOLTAMMETRIC DETERMINATION OF THALLIUM AS [TLBR4]-RHODAMINE-B COMPLEX

The anodic stripping voltammetric behaviour of the [TlBr4]-rhodamine B complex is described and compared with that of thallium(I) and thalli um(III) ions. The electrolyte composition, the best potential for the deposition of thallium from the complex in the selected electrolyte, t he duration of the electrolysis, and the possibility of reduction of t hallium in the [TlBr4]-rhodamine B complex before the electrolysis wit h ascorbic acid were investigated. The results showed good reproducibi lity of the measurements of thallium as [TlBr4]-rhodamine B complex an d are similar to those obtained for thallium as Tl(I) and Tl(III) ions . As the [TlBr4]-rhodamine B complex is strongly adsorbed on polyethyl ene, a previous preconcentration step on a column, packed with polyeth ylene powder, allowed the voltammetric determination of thallium as [T lBr4]-rhodamine B complex in samples of KCl and NaCl as solid salts af ter the separation of the matrix. With this procedure it was possible to reach enrichment factors of 25 with recoveries from 96.7 to 107.9% for thallium concentrations from 5 to 40 mu g L-1 and RSD between 4.2 and 9.2%. The procedure was used to determine thallium traces in KCl a nd in sea salt. The results of these determinations were compared with the results obtained by graphite furnace atomic absorption spectromet ry.