Asymmetric cellulose acetate membrane-based carbonate- and chloride-selective electrodes

The potentiometric response characteristics and analytical applications of asymmetric cellulose triacetate (CTA) membrane systems are examined by employing trifluoroacetophenone derivatives and metalloporphyrins as the carbonate and chloride ionophores, respectively. The asymmetric membranes are characterized by having a hydrophilic, porous layer on top of the sensing surface of the ion-selective layer and by showing a decreased interference from large, hydrophobic anions by the kinetic and exclusion mechanism. The performance of the asymmetric membrane is optimized by employing different hydrolysis times or different plasticizers. A new approach of forming a hydrophilic layer is described in which asymmetric membranes are formed by hydrolyzing directly the surface of homogeneous, plasticized CTA-matrix ion-selective membranes containing ion carriers. The analytical utility of the asymmetric membranes is demonstrated by employing the chloride-selective asymmetric membrane for serum chloride measurements. It is shown that the asymmetric membrane-based chloride-selective electrode exhibits a remarkably reduced response to salicylate, compared to the conventional PVC-or unmodified CTA-matrix membrane electrodes.