Thalhum as tetrachlorothallate(II1) can be preconcentrated from hydrochlonc acid (10 3 M) on to a carbon paste electrode that IS chenucally modified wth an amon exchanger (Amberhte LA-21 This accumulation was performed under open-clrcmt conditions The ensmng measurement was done by differential-pulse voltammetry by reducing the thallate(II1) ions to Tl(0) during the eqmhbration pe.nod and then re-oxldlzmg it to Tl(1) when recording the voltammogram The electrode surface had to be conditioned wrth different concentrations of hydrochloric acid (1 to 10 and 10e3 M) before each accumulation step m order to generate a defmlte amount of ion-exchanging groups For repetltwe use, the electrode surface could be regenerated with an aqueous solution of ammoma (1 M) The dependence of the current response on the analytical parameters (composition of the paste, preconcentration tune, composttion of the solutions involved) was investigated A linear relationship between concentration of Tl(II1) and the voltammetnc signal was found unth the range of 0 l-100 mg 1-l For these concentrations the standard addition method could be appbed for analy-ncal evaluations The influence of other ions interfering m the determmation was mveswated The apphcabdtty of this method to practical samples (fly ash) was investigated Keywords Voltammetry, Carbon paste electrodes, Fly ash, Thallium Correspondence to IL Kalcher, Karl-Franzens Umversltat Graz, Instdut fbr Analytlsche Chenue, Umversltatsplatz 1, 8010 Graz (Austna) * On leave from Haman Umverslty, Haman (China) * On leave from LaTrobe Umverslty, Melbourne (Australia)