Abstract: This invention provides a polarographic/amperometric measuring sensor, particularly useful for transcutaneous determination of the oxygen partial pressure (tcpO.sub.2) in the blood by means of a Clark-type electrode arrangement. According to the invention the counter electrode, preferably made of a noble metal, is disposed about the insulating material encasing the working electrode and is preferably made of the same noble metal as the working electrode. The measuring sensor can also be provided with a pH electrode for simultaneous determination of the carbon dioxide partial pressure (tcpCO.sub.2) in the blood.

Abstract: Disclosed herein is a retainer assembly for applying a membrane to a physiological sensing unit for the transcutaneous determination of the magnitude of physiological quantities, particularly for measuring the partial pressure of gases in blood or the like. The assembly constitutes a preassembly of a membrane, with a clamping ring accommodating the membrane and having an annular recess receiving the rim of the membrane. The clamping ring has a lip in the form of an inwardly protruding annular edge for removably securing the clamping ring together with the membrane to the sensing unit by virtue of the lip resiliently snapping into a peripheral groove of the sensing unit, the lip defining the periphery of the annular recess. A retainer element is provided for temporarily and removably assembling the membrane with the clamping ring prior to assembly with the sensing unit.