Measuring Cation Activity of Living Brain

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Abstract
Recent development of special glasses capable of discriminating sodium and potassium ions has made possible a method for recording the concentration of these ions in vivo.4-6,8,9 Electrodes made from these glasses function exactly like the common pH (hydrogen ion) electrode. In fact, in an acid solution, the sodium and potassium electrodes may be used to measure pH. However, in a sodium or potassium salt solution above pH 6, the response to hydrogen ion activity is negligible and the electrodes respond essentially only to changes in sodium or potassium ion activity. In the same manner a pH electrode will respond to changes in sodium and potassium ions above pH 11. When one of the three types of electrodes and a reference electrode are placed in a solution of these ions and connected to a high impedance voltmeter such as a pH meter, a potential is produced which is related to