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 ions down to a concentration of 2. 10(-8) mol 1(-1). The working principle of the reactrode is that thallium ions can be pumped into Prussian blue during alternating oxidation-reduction cycles. After a preconcentration 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 potassium ions. Cd(2+), Fe(3+), Zn(2+), Cu(2+) and Ni(2+) do not interfere up to a hundredfold excess, NH(4)(+) does not interfere up to a thousandfold - and Bi(3+) up to tenfold excess. The interference by Pb(2+) can be suppressed with EDTA.