THE EFFECTS OF COVALENT BINDING OF THE ELECTROACTIVE COMPONENTS IN DURABLE CHEMFET MEMBRANES - IMPEDANCE SPECTROSCOPY AND ION SENSITIVITY STUDIES

The effects of covalent attachment of the electroactive components (i. e. the cation receptor molecules and the tetraphenylborate anions) in durable CHEMFET membranes is described. CHEMFETs for monovalent cation s having either one or both electroactive components covalently bound in the membrane matrix exhibit Nernstian responses and good selectivit ies for Na+, or K+ ions, however, covalent attachment of berate in the membrane results in non-functioning sensors. Durability studies with CHEMFETs modified with polysiloxane membranes which are selective for Na+, K+ and Pb2+ ions show long lifetimes upon continuous exposure to a water stream. Na+ selective CHEMFETs with covalently attached Na+ io nophores and free berate in the membrane are still Na+ selective after 82 weeks of continuous exposure to water. Similar K+ and Pb2+ selecti ve polysiloxane CHEMFETs showed good selectivities for at least 26 and 19 weeks, respectively. Impedance measurements showed that in all cas es the lowest membrane resistance and the most stable CHEMFETs were ob tained with polysiloxane membranes containing covalently attached ion- selective calix[4]arene-based receptor molecules and free anionic site s. (C) 1998 Elsevier Science S.A. All rights reserved.