Preparation of microelectrodes: Comparison of polishing procedures by statistical analysis of voltammetric data

Manual and instrumental procedures for polishing 1 and 6 mu m radius platinum microdisc electrodes were compared by performing a statistical evaluation of three basic electrochemical signal characteristics measured from steady-state voltammmograms for oxidation of ferrocene in acetonitrile. The three signal characteristics measured were the limiting current I-lim, the half-wave potential E(1/2) and the (E(3/4) - E(1/4)) potential difference, where E(3/4) and E(1/4) are the potentials at three quarters I-lim and one quarter I-lim, 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 E(1/2) and (E(3/4) - E(1/4)) potential measurements, being +/-0.20 and +/-0.36 mV for E(1/2) values and 0.11 and 0.19 mV for (E(3/4) - E(1/4)) at 1 and 6 mu m electrodes, respectively. The instrument designed for polishing microelectrodes is also described.