Copper-film electrodes for Pb(II) trace analysis and a detailed electrochemical impedance spectroscopy study

The analytical performance of differently prepared in situ copper-film glassy carbon electrodes (CuFE) was compared with the bare glassy carbon electrode (GCE) for the electroanalytical determination of Pb(II) traces in a solution containing 0.1 M HCl and 0.4 M NaCl. Electrodes were prepared and validated for different accumulation potentials in order to check the influence of hydrogen evolution on the performance of the methods. The methods were first validated for limit of detection, linear concentration range, sensitivity, accuracy, and precision. The applicability of the CuFE method was also tested in a real sample analysis (local tap water). The main focus of this work is to understand the electroanalytical behaviour of such systems by performing a detailed electrochemical impedance spectroscopy (EIS) study at potentials that are more negative, just before, and more positive than the Pb(II) stripping signal develops. For comparison, the same analysis was also performed for the bare GCE. Moreover, the EIS spectra were also obtained at the open circuit potential in order to test the electrodeposited material. Different equivalent electrical circuits were employed in order to fully describe the situation on the electrodes surface. It was shown that the CuFE system is under kinetic control when the stripping signal is obtained, whereas it is under both kinetic and diffusion control at potentials more positive than the Pb (II) stripping peak potential. On the other hand, in the case of the bare GCE, the system is under both kinetic and diffusion control even before the analytical signal is obtained. This is the main electroanalytical difference between the modified and the non-modified electrodes and might be responsible for the differences in their analytical performances.