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A square-wave voltammetry (SWV) detection method for capillary electrophoresis (CE) using end-capillary detection is investigated. Although sensitive detection methods have been reported using off-capillary electrochemical detection methods, these methods typically use fragile carbon fiber electrodes and complex decoupling apparatus to separate the high separation voltage from the detection electronics. While end-column detection systems are not usually as sensitive as off-column techniques, they require much simpler instrumentation and are more robust. By modifying the Osteryoung SWV method to accommodate the high-frequency sample rate required by CE, a detection limit of 5 × 10-7 M (S/N = 10) was obtained for dopamine using end-capillary detection, which is comparable to sensitivities obtained using off-capillary detection with amperometric detection.

A new detection method was developed that takes advantage of changes in cyclic voltammograms (recorded with either a platinum or a gold ultramicroelectrode) caused by the adsorption, of inorganic and organic molecules. These changes may include reduction or oxidation of the adsorbate, inhibition of oxygen adsorption, inhibition of hydrogen adsorption, and also changes in the charging current. The detection is carried out in a stripping mode after the accumulation of analyte on the electrode surface for 50–1000 ms. Typical scan rates are between 10 and 1000 V/s. Removal of oxygen from the solutions studied is not required. Electrochemical conditioning of the working electrode is sufficient to insure a stable response for a period of several hours. For strongly adsorbing molecules the linear dynamic range extends over two orders of magnitude from about 10−7 M to 10−5 M with the relative standard deviation for replicate determinations lower than 5%. The smallest discernable signal is associated with about 0.1% surface coverage, which corresponds to the adsorption of about 10−18 mol of analyte on a ultramicroelectrode 5 μm in radius. Keywords: adsorption, cyclic voltammetry, ultramicroelectrode, flow injection.

An experimental setup for carrying out faradaic rectification measurements at micrometer-sized electrodes under potential control is described. A new method of data analysis is proposed that allows the determination of the standard rate constant and the electron-transfer coefficient of a fast charge transfer process without knowing the impedance of the microelectrode. This method is based on the frequency dependence of the shape of the faradaic rectification voltammograms (i.e., the average width of the peaks and the ratio of the peak heights) rather than on the magnitude of the faradaic rectification signal. The method was tested in the determination of heterogeneous electron transfer kinetics of Fe(CN)6(3-/4-) and Ru(NH3)6(2+/3+) in aqueous solutions on a platinum microelectrode (12.5 microm in radius) and ferrocene/ferrocinum redox couple in a dimethylformamide solution on a gold microelectrode (12.5 microm in radius).