ASYMMETRIC MEMBRANE-BASED POTENTIOMETRIC SOLID-STATE ION SENSORS

Asymmetric ion-selective membranes are shown to be advantageous for th e fabrication of solid-state ion sensors. These membranes have a hydro philic, porous layer on top of the sensing surface of the ion-selectiv e layer. Compared to conventional polymeric membranes, the asymmetric membranes show decreased interference from large, hydrophobic anions b ecause of kinetic and exclusion mechanisms. Cellulose acetate-matrix a symmetric 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 hy drophobic plasticized polyurethane membrane containing the appropriate ion carrier. Asymmetric membrane-based carbonate and chloride ion sen sors 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 .