A study of pencil-lead bismuth-film electrodes for the determination of trace metals by anodic stripping voltammetry

This work reports the utility of inexpensive and disposable pencil-lead graphite as a substrate for bismuth-film electrodes (BFEs) for the simultaneous determination of Cd(II), Pb(II) and Zn(II) by square-wave anodic stripping voltammetry (SWASV). The BFE was generated in situ by depositing simultaneously the bismuth film and the metal cations by reduction at -1.4 V on the pencil graphite substrate. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from -1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. Using the selected conditions, the limits of detection were 0.3 (mu)g l^-1 for Cd and 0.4 (mu)g l^-1 for Zn and Pb at a preconcentration time of 10 min and these values could be further decreased by the use of Nafion-covered pencil-lead BFEs. Finally, the pencil-lead BFEs were successfully applied to the determination of Pb and Zn in tap water with results in satisfactory statistical agreement with atomic absorption spectroscopy.