Physicochemical Characteristics of Antimony Microelectrode with Special Reference to Selection of Standard Buffers

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Abstract
Antimony (Sb) microelectrodes with tips of 2 to 5 .mu.m in outside diameter were constructed, and their electromotive forces (EMF) were tested in response to the pH of several calibration buffers. The data were compared with those of glass pH electrodes. Increasing ionic strength (I) caused a significant deviation in pH readings of the Sb-microelectrode (.delta.pHSb-Glass). Even with the correction for ionic strength, the values of .DELTA.pHSb-Glass were dependent on the nature of calibration buffers employed. Among various buffers, Tris buffer [Tris(hydroxymethyl)aminomethane(THAM)] had the least disturbance on the Sb-microelectrode, and bicarbonate had also relatively minor effect. The pH value according to the Sb-electrode was caused to deviate considerably by phosphate. The effect of phosphate within the range of 1 to 67 mM can be predicted by 1/.DELTA.pHSb-Glass = 1 + (0.174/[PO4]). Like phosphate, BES [N, N-Bis (2-hydroxyethyl)-2-aminoethanesulfonic acid] also had a significant effect on the EMF of the Sb-microelectrode. Upon consideration of the above facts, measurements of several biological fluids such as those of the in vivo pH of intratubular fluid of bullfrog kidney were carried out with the Sb-microelectrode calibrated by 90 mM Tris buffer. The Sb-microelectrode when properly calibrated can be used for the pH measurement of ultraminute amounts of biological samples.