Voltammetric determination of surface active compounds at Au and Pt ultramicroelectrodes in flowing solutions

Abstract

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.