Carbon paste electrodes bulk-modified with Bi(2)O(3)were used for the determination of Cd(II) and Pb(II). The best composition was 1% (wt%) Bi(2)O(3) in the paste. The measurements were made by differential pulse voltammetry in the potential range from -1.2 V to -0.3 V. The peak potential of the reoxidation of Cd is -0.85 V, and of Pb -0.60 V vs. SCE. The lowest concentration that could be determined was 5 microg L(-1) of both metals (preconcentration time 240 s), the relative standard deviation was 3.5%-5.0% (four determinations). The correlation coefficient ( r(2)) of the calibration curves was 0.9966 (for Cd) and 0.9971 (for Pb). The Bi(2)O(3)-modified electrode could be used for the analysis of drinking water, mineral water and urine.
Bismuth film electrodes (BiFE) prepared by plating a glassy carbon support ex situ from a solution containing 0.5 M LiBr and 1 M HCl was tested for the determination of cobalt traces using adsorptive stripping voltammetry (AdSV) and catalytic adsorptive stripping voltammetry (CAdSV). AdSV enables one to determine cobalt as the Co(II)-dimethylglyoximate (Co-DMG) complex down to 0.3 mg/L Co. Addition of NaNO 2 to the solution containing dimethylglyoxime in ammonia buffer provides a 15-fold enhancement of the voltammetric signal of cobalt due to the catalytic effect occurring during the reduction of Co(II)-DMG. Utilization of the bismuth film electrode under optimized conditions assures a stable catalytic adsorptive stripping voltammetric response for Co, with an extremely high sensitivity (1.75 mA/(mg/L)), good precision (RSD 3%), and a low detection limit (0.07 mg/L Co with 60 s of adsorptive accumulation). The results of the measurement of the catalytic cobalt response in the presence of DMG and nitrite under hydrodynamic amperometric conditions have shown the BiFE to be an attractive and suitable tool for the rapid determination of cobalt at low mg/L level in both batch and flow systems.
An attempt is made to describe the electrochemical properties of bismuth films, plated in-situ on glassy carbon in acetic buffer, over a broad range of deposition potentials. It is shown that accumulation during anodic stripping voltammetric determination of lead and zinc at the bismuth film electrode depends to a large extent on the electrolyte composition and the plating parameters. The influence of the plating potential on Pb deposition is moderate, but it could not be disregarded during Zn quantification. The sources of electrode poisoning effects are discussed in detail. Voltammetric studies are complemented by AFM microscopic observations.
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