Potentiometric selectivities of a plasticized poly(vinyl chloride) (PVC) membrane containing a hydrophobic quaternary ammonium salt and triphenyltin chloride (TPTCl) for several inorganic anions were evaluated by measurements of the membrane potential of a bi-ionic system (the so-called bi-ionic membrane potential). The addition of TPTCl to the plasticized PVC membrane containing a quaternary ammonium salt gave rise to selectivity patterns different from the Hofmeister anion series, which is observed for a membrane containing only the quaternary ammonium salt. The change in the selectivity pattern from the Hofmeister to the non-Hofmeister was observed under conditions where the TPTCl concentration was higher than the quaternary ammonium salt in the membrane. Response mechanisms and the selectivity of the TPTCl-based electrode are discussed with respect to the concentration dependence of TPTCl and quaternary ammonium salt in the membrane.
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