Determination of trace bismuth by under-potential deposition-stripping voltammetry at mesoporous platinum microelectrodes: application to pharmaceutical products

A methodology for the determination of bismuth, based on under-potential deposition-stripping voltammetry (UPD-SV), was investigated. It makes use of mesoporous platinum microelectrodes (Pt-MEs) prepared by a liquid crystal templating technique. The mesoporous microelectrodes, which are characterised by a very high surface area, allowed the accumulation of relatively large amounts of bismuth at under-potential without saturation of the electrode surface. Calibration plots for quantification of bismuth at micromolar levels were constructed by using the charge involved in either the anodic or cathodic peak recoded by cyclic voltammetry that ensued the accumulation of bismuth at the electrode surface. During the anodic scan, the oxidation of metallic bismuth occurred; the cathodic scan involved irreversibly adsorbed bismuth species, which are retained on to the electrode surface. The reproducibility of the proposed UPD-SV procedure (which was within 5 %) was assured by the application to the Pt-MEs of a suitable potential waveform, properly designed to avoid memory effect due to the irreversibly deposited bismuth. The latter phenomenon along with UPD allowed to overcome interference due to copper, which is normally observed when quantification of bismuth is performed by anodic stripping voltammetry at solid electrodes involving bulk metal deposits. The usefulness of the proposed method for the determination of bismuth in real samples was demonstrated by the analysis of a tablet of a pharmaceutical preparation, which is used for curing ulcers.