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 mu m) for end-capillary detectio n in capillary electrophoresis with metal ions as test analytes; some studies were also done with 25-mu m Pt disk electrodes. The waveform a pplied to the electrode consisted of a preconcentration period (55-330 ms) followed by cyclic voltammetry (2-100 ms). Maximum signal-to-nois e was obtained with the integrated CV current as the analytical signal , and this was linearly proportional to sweep rate; maximum response w as obtained at sweep rates of >100 V/s for 10-mu m electrodes and >200 V/s for 25-mu m electrodes; sweep rates of >400 V/s caused peak taili ng due to trapping of the analyte at the electrode. With this CV detec tion approach, comigrating analytes could be identified and determined . Reproducibilities for six analytes over the range 1.0 x 10(-7)-1.0 x 10(-5) mol/L were 2%-5%, and calibration curves were linear, with res ponse factors in the range of 2%-6%. Detection limits (2 x peak-to-pea k baseline noise) were in the range of 5 x 10(-9)-4 x 10(-8) mol/L, wh ich are 1-2 orders of magnitude better than results obtained previousl y with square-wave pulsed amperometric detection of metal ions.