Recognition of Inorganic Anions by Hydrogen Bonding Ionophores and Their Use for Ion-Selective Potentiometry

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(1) To support the development of new ion-selective electrodes for real-life samples from a thereotical side, the model explaining apparently "non-Nernstian" equilibrium responses was extended. It now also takes into account responses governed by a pair of a cation and an anion. Previous work had only taken into account responses governed by two ions of the same charge sign.(2) As an application of the model for apparently "non-Nernstian" responses, the responses of porphyrin-based fluoride ISEs were investigated. The unusual responses of those electrodes, which had not been understood for many years, could be explained by different stoichiometries of the complexes of the primary and the secondary ion.(3) Taking advantage of the model for apparently "non-Nernstian" responses, thermodynamic parameters of Ca2+ selective electrodes based on an ionophore with a positive charge were determined. These parameters were used to rationalize the experimental lifetime and selectivity changes of this ISE in long-term experiments. A quantitative model to explain these selectivity changes was developed.(4) As a further contribution to the theory of ISEs, the first general model explaining the selectivity of ISEs based on charged ionophores and added ionic sites was presented. It allows to rationally optimize the selectivity of these ISEs.