Anodic stripping voltammetric determination of thallium as [TlBr4]-rhodamine B complex

Abstract

The anodic stripping voltammetric behaviour of the [TlBr₄]-rhodamine B complex is described and compared with that of thallium(I) and thallium(III) ions. The electrolyte composition, the best potential for the deposition of thallium from the complex in the selected electrolyte, the duration of the electrolysis, and the possibility of reduction of thallium in the [TlBr₄]-rhodamine B complex before the electrolysis with ascorbic acid were investigated. The results showed good reproducibility of the measurements of thallium as [TlBr₄]-rhodamine B complex and are similar to those obtained for thallium as Tl(I) and Tl(III) ions. As the [TlBr₄]-rhodamine B complex is strongly adsorbed on polyethylene, a previous preconcentration step on a column, packed with polyethylene powder, allowed the voltammetric determination of thallium as [TlBr₄]-rhodamine B complex in samples of KCl and NaCl as solid salts after 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 μg L^–1 and RSD between 4.2 and 9.2%. The procedure was used to determine thallium traces in KCl and in sea salt. The results of these determinations were compared with the results obtained by graphite furnace atomic absorption spectrometry.