A detailed electrochemical impedance spectroscopy study of a bismuth-film glassy carbon electrode for trace metal analysis.

A systematic electrochemical impedance spectroscopy (EIS) analysis at different potentials of an in situ-prepared bismuth-film glassy carbon electrode (BiFE) in 0.1 M acetate buffer solution is reported. This electrode is employed in the square-wave anodic stripping voltammetry (SWASV) technique for the determination of trace amounts of the heavy metals Zn, Cd, and Pb. The method was first validated for detection limit, linear range, sensitivity, precision and accuracy to clearly prove the superior action of BiFE compared with the bare glassy carbon electrode (GCE). Next, in order to investigate the characteristics of this sensor, EIS measurements were carried out at slightly more negative potentials than the potentials at which each individual stripping signal is detected, after the deposition step at different deposition potentials. For comparison, EIS measurements were also performed at open circuit potential. The studied trace metal concentration range (5-20 ppb) did not significantly influence the capacitive and resistive behaviour of the BiFE which explains why the performance of this sensor is superior compared with the bare GCE. The higher sensitivity of the SWASV method for BiFE compared with the bare GCE was explained by the lower polarisation resistance values of the former. Moreover, the potential of zero charge was also determined, and an explanation whether the system is under kinetic- and/or diffusion-controlled process is given.