GB882143A - Electrode - Google Patents

Abstract

882,143. Electrode assembly. BECKMAN INSTRUMENTS Inc. Nov. 24, 1959 [Feb. 6, 1959], No. 39771/59. Addition to 838,980. Class 37. In an electrode assembly in which spaced measuring and reference electrodes are arranged in an electrolyte separate from a medium on which measurements are to be made by a selectively permeable membrane as described in the parent Specification, the maximum diameter of the measuring electrode is of the same order of magnitude or smaller than the thickness of the membrane. The assembly is shown, Fig. 1, installed in a needle 10, having a body 11, flange 12 and pointed hollow tube 13. The lower end of the assembly, Fig. 2, comprises a closed tube 18 of non-conducting material such as glass with a conductor 20 serving as the sensing electrode sealed in its end, the conducting material being preferably platinum. The conductor is encased in a silver jacket 21 for strength, and the tip is made flush with the end of the tube and the outer surface of the end 19 is covered with minute pits. A tube 23 of conducting material such as silver, serving as a reference electrode is cemented to tube 18 and is formed with an annular ring 24 at its end with an adjacent conical section 25. A membrane 27 is positioned over the end 19 and ring 24 thus defining an annular space 26 which is filled with electrolyte and so a thin film is supported by the pitted surface 19. Such an assembly can be made small enough to fit into an hypodermic needle and thus can be used to determine the oxygen content of the blood; in such a case the membrane may be of polyethylene. The sensing electrode 20 is made the cathode and the reference electrode the anode and the electrical characteristics of the cell are affected by the quantity of oxygen passing through the membrane. The cell current is directly proportional to the quantity of oxygen passing into the electrolyte and a typical circuit is shown in Fig. 4. The particular electrolyte used depends on the electrode materials and substance to be detected. The membrane is held in position by a sleeve 30 having a frusto-conical end 31. The tube 23 is cemented in an inner shell 35 which has an externally threaded housing at its upper end into which project the tube 18 and conductor 21. An insulating sleeve 37 is fitted around the tube 18 over the end of which the conducting pin 38 is fitted, having an electrical connection with 21. In a modification, Fig. 3 (not shown), a smooth outer surface is provided for the instrument, suitable for use in a catheter. The membrane may be made of two or more layers to reduce effects of temperature, viscosity and solubility of the constituent under investigation.