Asymmetric membrane-based potentiometric solid-state ion sensors

Abstract

Asymmetric ion-selective membranes are shown to be advantageous for the fabrication of solid-state ion sensors. These membranes have a hydrophilic, porous layer on top of the sensing surface of the ion-selective layer. Compared to conventional polymeric membranes, the asymmetric membranes show decreased interference from large, hydrophobic anions because of kinetic and exclusion mechanisms. Cellulose acetate-matrix asymmetric membranes are formed by hydrolyzing directly the surface of homogeneous, plasticized cellulose triacetate ion-selective membranes. The polyurethane-based asymmetric membrane system consists of a very thin hydrophilic polyurethane membrane coated on an underlying more hydrophobic plasticized polyurethane membrane containing the appropriate ion carrier. Asymmetric membrane-based carbonate and chloride ion sensors exhibit a remarkably reduced response to salicylate when compared to the PVC, unmodified cellulose triacetate, or polyurethane membrane-based ion sensors. The polyurethane-based asymmetric membrane system is especially promising for the fabrication of solid-state ion sensors.