Cyclic voltammetric detection in capillary electrophoresis with application to metal ions

Fast cyclic voltammetry (CV) was evaluated over sweep rates of 20-1000 V/s at Au disk electrodes (25 and 10 μm) for end-capillary detection in capillary electrophoresis with metal ions as test analytes; some studies were also done with 25-μm Pt disk electrodes. The waveform applied to the electrode consisted of a preconcentration period (55-330 ms) followed by cyclic voltammetry (2-100 ms). Maximum signal-to-noise was obtained with the integrated CV current as the analytical signal, and this was linearly proportional to sweep rate; maximum response was obtained at sweep rates of >100 V/s for 10-μm electrodes and >200 V/s for 25-μm electrodes; sweep rates of >400 V/s caused peak tailing due to trapping of the analyte at the electrode. With this CV detection approach, comigrating analytes could be identified and determined. Reproducibilities for six analytes over the range 1.0 × 10(-)(7)-1.0 × 10(-)(5) mol/L were 2%-5%, and calibration curves were linear, with response factors in the range of 2%-6%. Detection limits (2 × peak-to-peak baseline noise) were in the range of 5 × 10(-)(9)-4 × 10(-)(8) mol/L, which are 1-2 orders of magnitude better than results obtained previously with square-wave pulsed amperometric detection of metal ions.