An oxystat for the control of oxygen pressure in aqueous solutions

In the study of metabolic reactions, it is frequently desirable to observe the oxygen concentration in a solution that bathes the tissues under study to obtain a measure of the rate of oxygen utilization. Typically, either the oxygen is depleted in a matter of minutes and the test terminated or the ratio of solution to tissue is so large that meaningful measurernents are difficult. For tests in which the oxygen is taken from the surrounding gas, Wager and Porter (1961) have described a solution to the problem in which a manometric measurement of p02 con trolled the electrolytic production of oxygen which then had to be released into the atmosphere surrounding the tissue. The instrument described here also employs a pO2 measurernent to control the electrolytic production of oxygen, but a much greater speed of response is obtained by 1) the use of a Clark-type electrode for PO2 measurement, and 2) producing the oxygen directly in the solution that surrounds the test material. The hydrogen that is also formed in the electrolysis is sufficiently isolated from the tissue under test that no noticeable effects are produced. Furthermore, agreement between the net electrical charge involved in the electrolysis and the resulting amount of oxygen produced was within 5%, using published values" of the partial pressure of oxygen in air-saturated water as a standard.