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 TlI at open circuit. The accumulated TlI, after reduction to metallic thallium at the electrode surface, was anodically stripped by differential pulse voltammetry. Under optimized conditions, TlI 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 TlI 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 BiIII, PbII and CuII 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 TlI while masking TlIII with EDTA followed by chemical reduction of TlIII to TlI with hydroxylamine hydrochloride. This method was tested using a synthetic sample containing known concentrations of TlI and TlIII.