Abstract
Two kinds of pH-sensitive microelectrodes were constructed:
1) glass microelectrode with a pH-sensitive tip of 50-100 μm in length, and 2) antimony (Sb) microelectrode with a tip of 1-5 μm in outside diameter. Comparisons of the two were made on the change in the electromotive force (EMF) in response to various pHs and biological applicability.
The pH sensitivity (slope constant) at 20°C of the glass and Sb-microelectrodes averaged 51.7 and 51.9 (-mV/pH), respectively. Over the pH range of 2 to 9, both electrodes responded linearly to the change of pH. The pH-dependent EMF of the Sb-microelectrode was influenced by phosphate buffers, but not by Tris-HCl buffers. Though the glass microelectrode showed a linear response to all the buffers tested, its slope constant tended to be limited by the surface area of the pH-sensitive tip.
The stability of the EMFs was well within 1mV for 12hr with the glass microelectrode but more than 10mV with the Sb-microelectrode. On the other hand, the 95% response time was about 1min with the glass microelectrode, whereas it was less than a few seconds with the Sbmicroelectrode.
Blood pH was measured with the two electrodes and reasonable values were obtained with both methods, although the values by use of the Sbmicroelectrode were slightly higher than those of the other.
In view of the practical ease of manufacturing, maintenance and durability, the use of the Sb-microelectrode in biological measurement should also be re-evaluated, but several restrictions must be imposed on it.
