Analytical Sciences

Relationship between the Hydrophobicity of Cations and theCationic Response of a Plasticized Poly(vinyl chloride)Membrane Electrode with no Added Ion-Exchanger

Takashi MASADOME,*1 Toshihiko IMATO,*2Ž€Û´hin-ichi WAKIDA,*3 Kunishige HIGASHI,*3and Yasukazu ASANO*4

*1 Department of Chemical Science and Engineering, Ariake National College of Technology,Higashi-Hagio, Omuta, Fukuoka 836-8585, Japan
*2 Department of Chemical Systems and Engineering, Graduate School of Engineering, Kyushu University,Hakozaki, Higashi, Fukuoka 812-8581, Japan
*3 Department of Energy and the Environment, Osaka National Research Institute, Agency of Industrial Scienceand Technology, Ministry of International Trade and Industry, Midorigaoka, Ikeda, Osaka 563-8577, Japan
*4 Laboratory of Chemistry, Department of General Education, Ariake National College of Technology,Higashi-Hagio, Omuta, Fukuoka 836-8585, Japan

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 membraneelectrode and that of the ISFET electrode based on only the plasticizer to the cations, the response mechanism of the o-NPOE-plasticized PVC membrane electrode with no added ion-exchanger to the hydrophobic cations is discussed.

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