General Properties of Antimony Microelectrode in Comparison with Glass Microelectrode for pH Measurement

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Abstract
Two kinds of pH-sensitive microelectrodes were constructed: glass microelectrode with a pH-sensitive tip of 50-100 .mu.m in length, and antimony (Sb) microelectrode with a tip of 1-5 .mu.m in outside diameter. Comparisons of the 2 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.degree. 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 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 1 mV for 12 h with the glass microelectrode but more than 10 mV with the Sb-microelectrode. The 95% response time was about 1 min with the glass microelectrode; it was less than a few seconds with the Sb-microelectrode. Blood pH was measured with the 2 electrodes and reasonable values were obtained with both methods, although the values by use of the Sb-microelectrode 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 restrictions must be imposed on it.