DIFFERENTIAL-PULSE STRIPPING VOLTAMMETRIC DETERMINATION OF THALLIUM WITH AN 8-HYDROXYQUINOLINE-MODIFIED CARBON-PASTE ELECTRODE

A carbon paste electrode incorporating 8-hydroxyquinoline was fabricat ed to selectively accumulate Tl-I at open circuit. The accumulated Tl- I, after reduction to metallic thallium at the electrode surface, was anodically stripped by differential pulse voltammetry. Under optimized conditions, Tl-I concentrations in the range 1.00 x 10(-8) M - 1.00 x 10(-5) M gave two linear regions due to different controlling factors for accumulation. A detection limit of 4.90 x 10(-9) M (1.00 ppb) was found for a 120-s accumulation. For 10 determinations of Tl-I at conc entrations of 1.00 x 10(-6) M and 1.00 x 10(-7) M, relative standard d eviations of 2.60% and 3.20% were obtained, respectively. Interference s from Bi-III, Pb-II and Cu-II could be removed by masking with comple xing agents such as sodium diethyldithiocarbamate, EDTA, sodium citrat e, etc. A method was developed for thallium speciation and analysis, b ased on the determination of Tl-I while masking Tl-III with EDTA follo wed by chemical reduction of Tl-III to Tl-I with hydroxylamine hydroch loride. This method was tested using a synthetic sample containing kno wn concentrations of Tl-I and Tl-III.