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 was carried out by differential pulse anodic stripping voltammetry after reducing the thallium(III) to metallic thallium in ammonia–ammonium chloride buffer (pH 10.00). Factors affecting the accumulation, reduction and stripping steps were investigated and an optimized procedure was developed. Under optimized conditions, a calibration plot for thallium(III) concentration in the range 5.00 × 10–10–1.60 × 10–5 mol l–1 gave two linear regions arising from different controlling factors during the accumulation step. A detection limit of 2.30 × 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 × 10–6 mol l–1 and 1.00 × 10–7 mol l–1 TIIII, relative standard deviations, sr, of 2.8 and 4.8% were obtained, respectively. Interferences from other ions and organic substances were examined. The developed method was applied to thallium determinations in sea-water and human urine samples.