Semi-empirical treatment of ionophore-assisted ion-transfers in ultrathin membranes coupled to a redox conducting polymer

Abstract

Applying spectroelectrochemistry to all-solid-state electrodes composed of poly(3-octylthiophene) (POT) and an ultrathin ion-selective membrane on top, it is possible to monitor the dynamic charge transfer (CT) in POT when this event is coupled to ion transfers (ITs) promoted by the absence/presence of a selective ionophore in the membrane. Herein, we report on a combination of empirical and theoretical evidence revealing that different molar ratios of the ionophore and the cation exchanger in the membrane result in the modulation of non-assisted and assisted ITs of different stoichiometries. This occurs upon the same anodic voltammetric scan. The use of the developed theory together with Sigmoidal−Boltzmann fittings of the experimental dynamic absorbance observed in the POT film permits calculating voltammograms with different ITs. An easy semi-empirical treatment additionally provides the calculation of binding constants related to the assisted transfers. Furthermore, the approach is suitable for both preferred and non-preferred ions by the ionophore, which additionally leads to the estimation of the selectivity profile of the POT-membrane system. The extra discovery about the number of electrons associated to the CT in the POT film is expected to propitiate further research towards maximizing peak resolution in the voltammetric experiments. In this context, the developed theory would help in future steps towards the prediction of voltammetric responses for multi-ionophore membranes backside contacted with new redox materials, prospecting hence new electrodes for multi-ion detection with optimized analytical features.