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Response and Diffusion Behavior of Mobile and Covalently Immobilized H + ‐Ionophores in Polymeric Membrane Ion‐Selective Electrodes
Author(s) -
Püntener Martin,
Fibbioli Monia,
Bakker Eric,
Pretsch Ernö
Publication year - 2002
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/1521-4109(200211)14:19/20<1329::aid-elan1329>3.0.co;2-v
Subject(s) - ionophore , chemistry , membrane , covalent bond , ion selective electrode , polymer chemistry , vinyl chloride , selectivity , analytical chemistry (journal) , inorganic chemistry , copolymer , chromatography , organic chemistry , polymer , catalysis , biochemistry
Transmembrane ion fluxes have been found to be highly significant for the functioning of some ion‐selective electrodes (ISEs). Their control is important for the realization of polyion sensors and of ISEs with extremely low detection limits, in which case concentration polarizations between the sample bulk and the membrane surface must be controlled or minimized. This article presents a fundamental study of the diffusion behavior of mobile and covalently immobilized ionophores in polymeric membranes. It is anticipated that these experiments will lay the foundation for the development of other ion‐selective membranes with optimized ion fluxes, as required for submicromolar detection limits. To visualize transmembrane ion fluxes experimentally, the H + ‐chromoionophore ETH 2439 is chosen for this work. As a first step, the diffusion coefficient D of this chromoionophore is determined here in poly(vinyl chloride) (PVC) membranes with various plasticizer contents. A linear dependence is found between log D and the percentage of PVC. Further, a new covalently immobilized H + ‐chromoionophore, ETH 2439‐PU has been prepared as a model ionophore by copolymerization of a diol derivative of ETH 2439 with poly(tetrahydrofuran) and 2,2,4‐trimethylhexamethylene diisocyanate. The response behavior of ion‐selective electrodes (ISEs) based on ETH 2439 and ETH 2439‐PU is comparable, with some loss of selectivity and linear response range with the immobilized ionophore. A highly basic inner solution induces a super‐Nernstian response around pH 6 with ETH 2439 but not with ETH 2439‐PU. The responses of ISE membranes based on the two ionophores and inner solutions of rather concentrated acetic acid and hydrochloric acid indicate that the transport of acetic acid does not depend on the mobility of the ionophore while that of HCl does. The results suggest that the immobilized ionophore truly behaves as such, and that transmembrane ion fluxes can be reduced if the transport process is ionophore‐mediated.