The Rapid Measurement of pH by the Glass Electrode

We have developed a comparatively simple and inexpensive apparatus that can be applied to the rapid determination of pH from 0.003 sec onward. This has been achieved by a combination of (a) a standard pH meter, (b), a driving-mixing arrangement of the Hartridge-Roughton type, and (c) a specially designed glass microelectrode. The glass electrode (2-mm diameter, 120-mm length) has a pH-sensitive tip about 0.5 mm long and has a resistance of 150 megohms at 20°. About 25 ml of reagents are needed for one observation. No significant physical effects (e.g. streaming potentials) have been observed. Thus a precision of ±0.005 pH unit is possible, which is essential for many biochemical studies. To test the performance of this apparatus we have studied the kinetics of dehydration of carbonic acid. The velocity constant for this reaction has been found to be 25.5 and 72.00 sec-1, respectively, at 25° and 37°.