Temperature coefficient of and oxygen effect on the antimony microelectrode

With regard to pH measurement of biological fluids in vivo with metal-metal oxide microelectrodes, the effect of temperature and partial pressure of oxygen on antimony (Sb) microelectrodes was examined, and pH of blood was estimated in the bullfrog. The temperature coefficient (dE/dt) of electromotive force (EMF) of Sb-microelectrodes in the range of 7 to 37 degrees C was -1.18 +/- 0.113 mV/degrees C (mean +/- SEM) in Ringer solution, whereas that of the pH glass electrode in the same solution was -0.43 +/- 0.035 mV/degrees C. When estimated in Tris buffer solution, it was -0.06 +/- 0.063 mV/degrees C for Sb-microelectrodes and 1.05 + 0.036 mV/degrees C for glass electrodes. The change of slope constant (alpha in -mV/pH) in the Sb-microelectrode due to temperature change could be predicted empirically from: alpha = 0.40 (t-25) + 55.3, where t represents the measuring temperature in degrees C. The resultant deviation of pH reading between Sb and glass electrodes, delta pHSb-Glass, may be expressed by: delta pHSb-Glass = 0.00183 (t-25) +0.016. In the range of 45 to 760 mmHg of oxygen partial pressure it fixed pH, the EMF increased linearly with the increase of Po2, the slope (dE/dlog(Po2)) being 11.7 +/- 0.42 (SEM) mV (n = 13, t = 25 degrees C). In consideration of the above effects, the blood pH of bullfrog was estimated to be 7.697 +/- 0.092 (SD) and 7.729 +/- 0.111 with glass and Sb-microelectrodes respectively, the difference between the two being relatively minor.