Electrochemical stripping analysis from micro-counter electrode

Abstract

Electrochemical stripping analysis (anodic, cathodic, or adsorptive) is usually based on the pre-concentration of a target analyte on the working electrode surface and then measuring its quantity via its direct quantitative electrochemical transformation (with the electrode refreshed afterwards). In this work, we demonstrate a new approach to carry out electrochemical stripping analysis of non-adsorbing species, thus not based on the analyte being directly pre-concentrated on the working electrode (WE), but on the signal obtained indirectly from the counter electrode (CE) where metal ions are reduced and then electrochemically stripped. Different from the CE with large surface area in classical electrochemical measurements, an ultramicroelectrode is chosen here as CE to purposely exploit the polarization effect. The concept is based on oxidizing the analyte on WE in one compartment of the electrochemical cell while reducing Cu2+ on CE from another compartment connected with an ionic bridge or a less common metal “bridge”. The deposited Cu on CE is then analyzed by stripping in another three-electrode cell, and the charge shows good linear relationship with the concentration of analyte in the former cell. As the stripping current response (peak) is much clearer than the small current variations corresponding to the direct oxidation of the analyte, it improves the resolution of raw signal. Besides, it may also reduce the background signal from blank solution by “filtering” the non-Faradaic charge. Like in classical electrochemical stripping analysis, one may also prolong the oxidation time in exchange for higher sensitivity of analysis. This work extends the applications of stripping analysis and offers a new angle of electroanalysis by capturing signals from counter electrode.