pH-ISFETs using tertiary amines as sensing material

pH ionophores were investigated using lipophilic tertiary amines for pH-ion-selective field-effect transistors (ISFETs) for acid-rain monitoring as an alternative sensing material of the conventional insulators to eliminate interference of charged contaminant. Among eight kinds of lipophilic tertiary amines, we found an excellent pH ionophore, a branched isomer of octylamine which shows an almost linear response range from pH 1.4 to pH 9.2. Using the pH-sensitive membrane, we prepared a prototype of FET-based pH checker composed of a pH-sensitive ISFET and a silver/silver chloride reference electrode and have demonstrated its preliminary application to real rain samples of rainwater. We could obtain good agreement of pH values obtained by the checker and the conventional pH glass electrode with correlation coefficient of 0.988.