DETERMINATION OF TRACE THALLIUM AFTER ACCUMULATION OF THALLIUM(III) AT A 8-HYDROXYQUINOLINE-MODIFIED CARBON-PASTE ELECTRODE

Thallium(III) was selectively accumulated, in an open circuit, from a stirred Britton-Robinson buffer solution (pH 4.56) onto a carbon paste electrode incorporating 8-hydroxyquinoline. The ensuing measurement w as carried out by differential pulse anodic stripping voltammetry afte r reducing the thallium(III) to metallic thallium in ammonia-ammonium chloride buffer (pH 10.00). Factors affecting the accumulation, reduct ion and stripping steps were investigated and an optimized procedure w as developed. Under optimized conditions, a calibration plot for thall ium(III) concentration in the range 5.00 x 10-(10)-1.60 x 10(-5) mol I -1 gave two Linear regions arising from different controlling factors during the accumulation step. A detection limit of 2.30 x 10(-10) mol l(-1) (0.047 ppb) (S/N = 3) was found for a 2 min accumulation. For 10 successive determinations of 1.00 x 10(-6) mol I-1 and 1.00 x 10(-7) mol l(-1) Tl-III, relative standard deviations, s(r), of 2.8 and 4.8% were obtained, respectively. Interferences from other ions and organic substances were examined. The developed method was applied to thalliu m determinations in sea-water and human urine samples.