Evaluation of carbon paste electrodes modified with 1-furoylthioureas for the analysis of cadmium by differential pulse anodic stripping voltammetry

Two series of 1-furoylthioureas (FTHD) were used as modifiers of carbon paste electrodes (CPEs) for the analysis of Cd(II). The capacities of the newly FTHD-modified CPEs were calculated and the surface reactions during the preconcentration of Cd(II) were studied by cyclic voltammetry. The analyte was accumulated on the surface of the modified CPEs by complexing with FTHD 3,3-disubstituted (series 1) and 3-monosubstituted (series 2) and reduced at a negative potential (−1.0 V). It was then quantified by differential pulse anodic stripping voltammetry (DPASV) in Britton–Robinson buffer at pH 4. Experiments were conducted to establish the optimal carbon paste composition, electrolyte and pH of the determination, accumulation potential and time, and instrumental parameters. Under the optimized working conditions good linear correlations were obtained for the calibration graphs in the concentration ranges studied. For 5 min of accumulation time, detection limits using modified CPEs with ligands of series 2 were lower than that of series 1 (6 × 10−5 mg L−1 versus 3 × 10−3 mg L−1, respectively, for the CPEs modified with 1-furoyl-3-p-tetradecylphenylthiourea and 1-furoyl-3-benzyl-3-phenylthiourea taken as models of both series). For a series of seven determinations of Cd(II) at 0.5 mg L−1 relative standard deviations below 3.9% were achieved for CPEs with ligands of both series. Only Pb(II) and Cu(II) apparently affected the electrochemical response of Cd(II).