title: Electrochemical methods for the determination of the diffusion coefficient of ionophores and ionophore-ion complexes in plasticized PVC membranes.
abstract: The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species.
authors.affiliation: Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gellért tér 4, 1111, Hungary.
authors.forename: Sándor
authors.initials: S
authors.lastname: Bodor
authors.forename: Justin M
authors.initials: JM
authors.lastname: Zook
authors.forename: Erno
authors.initials: E
authors.lastname: Lindner
authors.forename: Klára
authors.initials: K
authors.lastname: Tóth
authors.forename: Róbert E
authors.initials: RE
authors.lastname: Gyurcsányi
mesh_terms: D004058:Diffusion; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods; D006801:Humans; D017136:Ion Transport; D017736:Ion-Selective Electrodes; D007476:Ionophores / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008567:Membranes, Artificial; D010968:Plasticizers; D011143:Polyvinyl Chloride
chemical_list: D007476:Ionophores; D007477:Ions; D008567:Membranes, Artificial; D010968:Plasticizers; D011143:Polyvinyl Chloride