A PRUSSIAN BLUE-BASED REACTIVE ELECTRODE (REACTRODE) FOR THE DETERMINATION OF THALLIUM IONS

A reactive electrode (reactrode) made of Prussian blue (PB), graphite and paraffin can be used for a selective determination of thallium ion s down to a concentration of 2 . 10(-8) mol l(-1). The working princip le of the reactrode is that thallium ions can be pumped into Prussian blue during alternating oxidation-reduction cycles. After a preconcent ration of thallium ions in PB, the voltammetric determination follows as usually in anodic stripping voltammetry, i.e. the thallium ions are reduced to thallium metal which is subsequently oxidized to give the anodic stripping signal. The peculiarity of the Prussian blue-thallium system is that the thallium ions are situated in the holes of the PB matrix. When reduced to metallic thallium, they are substituted by pot assium ions. Cd2+, Fe3+, Zn2+, Cu2+ and Ni2+ do not interfere up to a hundredfold excess, NH4+ does not interfere up to a thousandfold - and Bi3+ up to tenfold excess. The interference by Pb2+ can be suppressed with EDTA.