ASYMMETRIC CARBONATE ION-SELECTIVE CELLULOSE-ACETATE MEMBRANE ELECTRODES WITH REDUCED SALICYLATE INTERFERENCE

The asymmetric carbonate ion-selective cellulose triacetate membrane electrodes are used to reduce salicylate interference for total CO2 measurements in human serum samples. The asymmetric membranes are formed by first casting a thin layer of cellulose triacetate without carrier, hydrolyzing one side of this thin film with base, and, subsequently, casting a second layer of cellulose triacetate containing the membrane active components [i.e., (trifluoroacetyl)-p-butylbenzene as a neutral ionophore]. The resulting asymmetric carbonate-selective membranes function equivalently, in terms of the carbonate response, to conventional PVC-based membranes. However, asymmetric membranes exhibited a reduced and slower response toward large lipophilic anions such as perchlorate or salicylate compared to PVC-based membranes, while both membranes showed similar response characteristics toward smaller hydrophilic anions such as carbonate. The asymmetric carbonate ion-selective membranes can be used to enhance the selectivity for carbonate ion over other large anions by employing either the flow-through or the equilibrium (static) arrangements. For preliminary applications, the asymmetric carbonate ion-selective membranes were utilized to determine total CO2 contents in flowing or static solutions containing salicylate interferences. It is shown that the asymmetric membranes are substantially less subject to salicylate interference compared to the conventional PVC-based membranes.