Abstract

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.

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Manual and instrumental procedures for polishing 1 and 6 pm radius platinum microdisc electrodes were compared by performing a statistical evaluation of three basic electrochemical signal characteristics measured from steady-state voltammograms for oxidation of ferrocene in acetonitrile. The three signal characteristics measured were the limiting current Ilim, the half-wave potential Ell2 and the (E3/4 -E1/4) potential difference, where E3/4 and E1/4 are the potentials at three quarters Zlim and one quarter Zlim, respectively. Fisher-Snedeckor F-test and Student's t-test statistical data are presented together with corresponding critical values for the three electrochemical parameters obtained in the manual and instrumental polishing modes. The reproducibility of all measured data is significantly improved when the electrode is polished after each experiment. The mean values of the limiting currents were significantly better using the instrumental rather than the manual polishing method. However, with respect to uncertainty of the experimental values, instrumental polishing gave the best estimates of the measured parameters; confidence intervals were very small for and (E3/4 -E1/4) potential measurements, being ltO.20 and lt0.36 mV for E1/2 values and 0.11 and 0.19 mV for (E314 -E1/4) at 1and 6 pm electrodes, respectively. The instrument designed for polishing microelectrodes is also described.

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