Indirect amperometric detection of non-electroactive species. towards an electrochemical bioasay of mineral weathering?

Abstract

Ion exchange polymers doped with a suitable electroactive mediator (i.e., Cu2+ or Fe(CN)63-) have been used to modify carbon paste electrodes that have been further applied to the indirect amperometric detection of non-redox cations or anions in flow injection analysis. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles located at the electrode surface, followed by the electrochemical transformation of the mediator species leached out of the polymer at the electrode/solution interface. Operating in the absence of added supporting electrolyte led to peak currents made of a major faradic component that is added to a capacitive contribution due to the conductivity jump occurring upon the analyte passing the electrode surface. The method can be applied to the detection of non-electroactive mineral cations and anions, as well as poorly-dissociated organic acids, which are usually involved in mineral weathering. After having characterized and discussed the main parameters affecting the sensitivity of the detection (with respect to analyte charge, size and degree of dissociation), the electrochemical device was evaluated as a possible test to monitor mineral weathering in a simple case (zeolite dissolution in acidic medium) and in a more sophisticated one (biomediated olivine dissolution by fungi).