The potential response of an electrode based on an o-nitrophenyl octyl ether (o-NPOE)-plasticized poly(vinyl chloride) (PVC) membrane with no added ion-exchanger to several cations of different hydrophobicity was examined. Furthermore, the hydrophobicity of the cations was evaluated by measuring the selectivity coefficient, K(Pot)/(Na,cation) of a sodium ion-selective electrode based on an o-NPOE-plasticized PVC membrane containing a cation exchanger, since the selectivity coefficient is closely related to hydrophobicity of the ions. From these results, the o-NPOE-plasticized PVC membrane electrode with no added ion-exchanger showed a Nernstian response to the cations for which the sodium ion-selective electrode has a selectivity coefficient, K(Pot)/(Na,cation) of more than 10(6.0). In addition, an electrode based on only the plasticizer (o-NPOE) was fabricated by using an ion-sensitive field-effect transistor (ISFET); the response of the electrode to the cations was examined in order to evaluate the contribution of the plasticizer, itself, to the electrode response of the PVC membrane electrode with no added ion-exchanger. From the response of the o-NPOE-plasticized PVC membrane electrode and that of the ISFET electrode based on only the plasticizer to the cations, the response mechanism of the oNPOE-plasticized PVC membrane electrode with no added ion-exchanger to the hydrophobic cations is discussed.
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