Measurement of Hydrogen Ion Concentration by Means of the Glass Electrode.

Abstract

Acidity plays such an important rôle in modern biology that the methods of measuring it are of considerable interest. A method has recently been introduced that is admirably adapted to many needs of experimental biology. The glass electrode is as accurate as the hydrogen electrode, as rapid as the quinhydrone electrode, and (once the apparatus has been set up) as easy to use as colorimetric methods. It can, moreover, be used under conditions when no other method is applicable—for example, for the direct measurement of the pH of whole blood.

The glass electrode was gradually developed over a period of fifty years by a number of investigators (including Lord Kelvin, 1 Cremer 2 and Haber 3 ); its recent application to the exact measurement of hydrogen ion concentration is due to Kerridge. 4 We have used it for this purpose, but to obtain satisfactory results we find it necessary to take a precaution that is hardly mentioned in previous papers on the glass electrode. At the same time, we have introduced several modifications that simplify and shorten the manipulations.

One form of electrode consists of a glass tube, one end of which is blown to a very thin bulb, a depression in which forms the membrane. If on the 2 sides of the membrane are placed 2 solutions of different pH, a potential difference is set up, and under certain conditions, this potential is determined by the difference in pH of the 2 solutions. Consequently, if the pH of one solution and the membrane potential are known, the pH of the other solution can be calculated. For the measurement of potential the current is led off from each solution by means of a KC1 bridge to a calomel half cell.