Differential pulse stripping voltammetric determination of thallium with an 8‐hydroxyquinoline‐modified carbon paste electrode

A carbon paste electrode incorporating 8‐hydroxyquinoline was fabricated 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 × 10 −8 M − 1.00 × 10 −5 M gave two linear regions due to different controlling factors for accumulation. A detection limit of 4.90 × 10 −9 M (1.00 ppb) was found for a 120‐s accumulation. For 10 determinations of Tl I at concentrations of 1.00 × 10 −6 M and 1.00 × l0 −7 M, relative standard deviations of 2.60% and 3.20% were obtained, respectively. Interferences from Bi III , Pb II and Cu II could be removed by masking with complexing agents such as sodium diethyldithiocarbamate, EDTA, sodium citrate, etc. A method was developed for thallium speciation and analysis, based on the determination of Tl I while masking Tl III with EDTA followed by chemical reduction of Tl III to Tl I with hydroxylamine hydrochloride. This method was tested using a synthetic sample containing known concentrations of Tl I and Tl III .