High-Frequency Impedance Spectroscopy of Platinum Ultramicroelectrodes in Flowing Solutions

A method for studying impedance spectroscopy of micrometer-sized electrodes in the frequency range from 5 kHz to 5 MHz has been developed and tested. Details of the electronic circuit and the data processing method are provided. Since the method involves high-speed data acquisition and fast Fourier transformation, the impedance data can be obtained within a 5-ms time window. This enables measurement of changes in the electrode impedance caused by rapid changes in the solution composition. In particular, the method is well suited to studying the performance of electrochemical microdetectors in flowing solutions. The performance of the method was tested in a brief study of the competitive adsorption of hydrogen and methionine on a Pt ultramicroelectrode. It has been shown that proper electrochemical conditioning can prevent any long-term changes in the properties of the electrode caused by its exposure to common organic or inorganic substances. Hence, it provides means for making an ultramicroelectrode with a virtually renewable surface. Alternatively, without electrochemical conditioning, it is possible to construct an adsorbed layer with desired properties by exposing the electrode to one or even several solutions for precisely controlled time periods.