Polymer-membrane electrode-based potentiometric sensing of ammonia and carbon dioxide in physiological fluids

Several new electrochemical devices designed for detecting ammonia and carbon dioxide in physiological samples have in common the elimination of the fragile glass pH internal electrode used in the conventional Severinghaus-design potentiometric gas sensors. In one new approach, the pH glass electrode can be replaced with a neutral carrier-based polymer-membrane pH electrode. Alternatively, to improve response characteristics and selectivity, we have used ion-selective polymer membranes responsive to ammonium and carbonate as internal sensing elements in conjunction with appropriate internal buffer reagents. The use of inner polymer membranes rather than glass membranes enables the fabrication of essentially disposable devices having rapid response times. In addition, we have constructed automated continuous-flow NH3- and CO2-sensing systems involving novel tubular forms of the polymer-membrane electrodes and a simple flow-through gas dialysis arrangement. The polymer electrode-based systems described offer many unique and practical advantages over existing gas-sensing units.