Description of the Effects of Non‐ion‐exchange Extraction and Intra‐membrane Interactions on the Ion‐selective Electrodes Response within the Interface Equilibria‐triggered Model

Abstract

The recently proposed interface equilibria‐triggered dynamic diffusion model of the boundary potential has proven its high predictive efficiency for quantification of the ion exchange and co‐extraction effects at the interface, as well as of the trans‐membrane transfer effect, on the electrode response. It is applicable for both ion exchanger‐based and neutral carrier‐based electrodes. In this communication, the adaptability of this model to more complex cases, when non‐ion‐exchange extraction processes at the interface (partition of organic acids’ and bases’ molecular forms and extraction of ionic associates) are coupled with protolytic equilibria in the aqueous phase and with self‐solvation process in the membrane phase, is demonstrated. By the example of electrodes reversible to ions of highly lipophilic physiologically active bases and acids (amiodarone, verapamil, vinpocetine, salicylic acid), it is shown that the peculiarities of their functioning, such as a very strong pH effect on the potential of cation‐selective electrodes, non‐monotonic pH dependence of the potential and super‐Nernstian response slope in certain pH region for a salicylate‐selective electrode, are well described within the model.

Potentiometric Sensing

“…The corrected concentration values are then further used to describe the diffusion processes in each phase in accordance with Fick’s laws. The high predicting ability of the interface equilibria-triggered dynamic diffusion model was further demonstrated by applying it to more complex cases, for example, where non-ion-exchange extraction processes at the interface (partition of neutral organic acids and bases and extraction of ionic associates) are coupled with protolytic equilibria in the aqueous phase and with a self-solvation process in the membrane phase . Moreover, Egorov and Novakovskii overcame another limitation of Morf’s finite-difference model that is related to the need for accounting for the change of the interfering ion concentration in the near-boundary water layer .…”

“…The high predicting ability of the interface equilibria-triggered dynamic diffusion model was further demonstrated by applying it to more complex cases, for example, where non-ion-exchange extraction processes at the interface (partition of neutral organic acids and bases and extraction of ionic associates) are coupled with protolytic equilibria in the aqueous phase and with a self-solvation process in the membrane phase. 16 the change of the interfering ion concentration in the nearboundary water layer. 17 In Morf's original finite-difference model, the concentration of the interfering ion in the boundary layer is assumed to be constant and equal to its concentration in bulk solution.…”

Ion exchanger‐based electrodes for determination of highly lipophilic physiologically active amines: Peculiarities of functioning and ways for improving analytical characteristics

“…In addition, quite significant opportunities to control the characteristics of such electrodes are provided by the choice of plasticizer [7]. However, as we have shown earlier, electrodes reversible to highly hydrophobic ions have their own specific behaviour, which is caused by the possibility of co-extraction of the analyte into the membrane [8,9]. Therefore, their analytical characteristics significantly depend on the measurement conditions, primarily on the choice of pH value.…”