Development of a miniature pH glass electrode with field-effect-transistor amplifier for biomedical applications

A miniature pH glass electrode for possible clinical and biomedical applications was constructed and evaluated in reference pH buffer solutions at 36°C. A field-effect-transistor (f.e.t.) amplifier was integrated into the system, and its effectiveness was investigated. The average e.m.f. efficiency of the developed electrode was 0·87±0·11V, and a minimum length of 7 mm was required for a good pH response. Temperature dependence of the electrode was -1·51 mV/^oK at a pH of 7. Evaluation of the stability of the electrode showed a 1% drift over a 7 h operational time. The pH and temperature hysteresis effects showed 0·5% and 1·0% deviations, respectively. The response time was within 4 s for 99% response. These electrode characteristics were also investigated in blood plasma and discussed.