HIGH-FREQUENCY IMPEDANCE SPECTROSCOPY OF PLATINUM ULTRAMICROELECTRODES IN FLOWING SOLUTIONS

A method for studying impedance spectroscopy of micrometer-sized elect rodes in the frequency range from 5 kHz to 5 MHz has been developed an d tested. Details of the electronic circuit and the data processing me thod are provided. Since the method involves high-speed data acquisiti on 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 compositi on. In particular, the method is well suited to studying the performan ce of electrochemical microdetectors in flowing solutions. The perform ance of the method was tested in a brief study of the competitive adso rption of hydrogen and methionine on a Pt ultramicroelectrode. It has been shown that proper electrochemical conditioning can prevent any lo ng-term changes in the properties of the electrode caused by its expos ure to common organic or inorganic substances. Hence, it provides mean s 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 t ime periods.