VOLTAMMETRIC BEHAVIOR OF THALLIUM(III) ON CARBON PASTE ELECTRODES CHEMICALLY MODIFIED WITH AN ANION-EXCHANGER

Thallium as tetrachlorothallate(III) can be preconcentrated from hydrochloric acid (10(-3) M) on to a carbon paste electrode that is chemically modified with an anion exchanger (Amberlite LA-2). This accumulation was performed under open-circuit conditions. The ensuing measurement was done by differential-pulse voltammetry by reducing the thallate(III) ions to Tl(0) during the equilibration period and then re-oxidizing it to TI(I) when recording the voltammogram. The electrode surface had to be conditioned with different concentrations of hydrochloric acid (I to 10 and 10(-3) M) before each accumulation step in order to generate a definite amount of ion-exchanging groups. For repetitive use, the electrode surface could be regenerated with an aqueous solution of ammonia (1 M). The dependence of the current response on the analytical parameters (composition of the paste, preconcentration time, composition of the solutions involved) was investigated. A linear relationship between concentration of TI(III) and the voltammetric signal was found with the range of 0.1-100 mg l-1. For these concentrations the standard addition method could be applied for analytical evaluations. The influence of other ions interfering in the determination was investigated. The applicability of this method to practical samples (fly ash) was investigated.