Impedimetric detection of chloride ions using two symmetric Ag/AgCl electrodes

Abstract

The suitability of Ag/AgCl electrodes for specific detection of chloride ions in aqueous gels is investigated. In contrast to potentiometric sensors, we use an impedimetric approach and avoid the need for a separate reference electrode through a symmetric two-electrode configuration. As such, electrochemical impedance spectroscopy is employed to characterise the response of the Ag/AgCl electrodes in contact with gels at various hydration levels containing different types as well as concentrations of salt. In order to extract quantitative information related to e.g. the ion concentration and mobility from the impedance spectra, an equivalent circuit model is fitted to the data. Here, we develop a simple equivalent circuit model related to the physical parameters of the system, which can be reduced to a modified Randles circuit with only few circuit elements. Importantly, even though the equivalent circuit model contains the same elements as a Randles circuit, their physical origin is different. Systematic variations of ion mobility, ion concentration, and type of ions allow us to evaluate the relationship between those physical properties and the resulting fitting parameters of the modified Randles circuit. This finally enables us to determine chloride concentrations in complex liquids, containing other salts and long chain molecules.