investigate a single electrode and thus a single event (see Figure 1). The current flows through the anode (electrode where oxidation happens) and the cathode (electrode where reduction takes place). So, both these electrodes influence the measured current and the current-limiting process cannot be determined. This is especially an issue in analytical chemistry. Another issue is concentration polarization. This is the effect of an electrode changing its environment and thus its potential during an electrochemical reaction. For most electroanalytical methods, a poten+ - Rf a) WE E I RE RE CE CE CE b) WE E I c) WE Vout - Vbias + Fig 1 - Current and potential in a two-electrode system (a) and in a three-electrode system (b), and the schematic of a potentiostat control circuit (c). Medical Design Briefs, June 2021 Cov www.medicaldesignbriefs.com ToC 15http://www.medicaldesignbriefs.com