Polarographic Oxygen Electrode1

A method has been developed for the continuous monitoring of oxygen tension in solutions and gases. The oxygen is reduced at a platinum surface which is covered with a plastic membrane. The silver-silver oxide reference electrode is also included under the membrane. Drift is less than 10 per cent for a period of days, and temperature compcnsation is possible. A number of uses to which it has been put arc described. The intimate involvement of oxygen in nature makes its measurement a problem of recurring interest. In many investigations prcscnt techniques of oxygen detcrmination limit the amount and type of data that can be taken. A method of continuously monitoring oxygen tension in liyuids and gases will bc described in this paper. It is based on the polarographic reduction of molecular oxygen at a platinum electrode. Many of the previous shortcomings of polarographic systems have been overcome. The variety of tasks to which it has been applied include the dctermination of biological oxygen demand in domestic sewerage, continuous flow respirometry of a variety of marine and freshwater invertebrates and fishes, determination of respiration and photosynthesis in algae, analyzing respiratory gases for oxygen, determination of oxygen tension in l-ml samples of water and biological fluids, and vertical profiles of oxygen in fresh and salt water. Interest has been sufficient to indicate that the technique should be published separately as a research method. An explanation of how the electrode functions will be followed by a description of some of the above uses to indicate its potentialities. A more complete description of the theory and chemical behavior of the electrode will be prcscntcd elsewhere. I. TII-EORY OF THE OXYGEN ELECTRODE The present system consists of a platinum electrode held at .8 volts to a silver-silver 1 Contribution No. 1014 from the Woods Hole Oceanographic Institution. oxide reference electrode. Molecular oxygen is rcduccd at the platinum surface, and a current flows. The magnitude of this current depends upon the amount of oxygen reaching the platinum surface. Thus a bare platinum electrode in sea water makes an acceptable polarograph for a short time. The sensitivity oji such an electrode decreases with time, apparently due to metals plating out on the platinum. The sensitivity cannot be regained by reversing the current. In complex biological media such as blood, red cells or other material usually collect on the surface and reduce the sensitivity by partially blocking the access of oxygen. Dropping mercury electrodes partly overcome the difficulty by continually renewing the metallic surface, but they are inconvenient and may bc poisonous to living systems. Such chemical and physical factors have prevented polarographic methods of oxygen determination from being widely used. In an effort to overcome the shortcomings of a bare platinum electrode in biological fluids, Davies and Brink (1942) covered the metal with agar and also a membrane of collodion, and Clark and colleagues (1953) later investigated a variety of other plastic films. A recent symposium has summarized the present state of the art (Fedcration Proceeding 11957). Interest in such systems has been mostly among biologists for application to specific problems. The present work was undertaken to develop a generally useful technique for biological and oceanographic work. Preliminary experiments with uncovered