Square-wave amperometric monitoring of reaction rates

Abstract

The application of square-wave amperometry, an analytical technique involving the use of two indicator electrodes polarized by a square wave, in the determination of reaction rates is described. Kinetic measurements have been made on the bromination of anisole in aqueous solution. Square-wave amperometry in conjunction with a stopped-flow apparatus equipped with Pt electrodes in the observation tube was used to monitor the disappearance of bromine in dilute solutions. Reaction rates with half-lives down to ca. 5 ms can be measured using relatively high-frequency square waves (ca. 800–1000 Hz). The results are in good agreement with values measured spectrophotometrically at higher bromine concentrations. The rate of dissociation of Ag⁺ from its macrobicyclic cryptand 211 complex was also measured, using a pair of silver indicator electrodes. Free Ag⁺ may be monitored selectively in the presence of its cryptate complex by using a low-amplitude square wave (± 150 mV). The advantages and limitations of the amperometric technique for kinetic measurements are discussed.