Apparatus for electrolytically determining a species in a fluid and method of use

• US 4,076,596 A
• Filed: 10/07/1976
• Issued: 02/28/1978
• Est. Priority Date: 10/07/1976
• Status: Expired due to Term

• Current Assignee: Leeds & Northrup Co.
• Original Assignee: Leeds & Northrup Co.
• Inventors: Connery, James Gerard, Muly, Emil Christopher, Taylor, Robert Morgan
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US05/730,409
• Time in Patent Office: 509 Days
• Field of Search: 204/195 P, 204/1 P, 204/1 B, 204/1 T, 204/195 R, 204/195 B, 128/2 E, 128/2.1 E, 324/29
• US Class Current: 205/780
• CPC Class Codes: G01N 27/404 Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid , e.g. Clark-type oxygen sensors
• CPC Class Codes: G01N 27/4075 Composition or fabrication of the electrodes and coatings thereon, e.g. catalysts

Abstract

An electrolytic cell for measuring the concentration of a species such as oxygen is constructed by depositing closely spaced interleaved inert electrode surfaces on the surface of an insulating substrate and covering the electrode surfaces with a thin film of electrolyte and permeable membrane. The electrolyte is selected so that the species being measured is generated at one electrode surface and consumed at the other with no net reaction in the electrolyte. Alternatively, a cylindrical configuration may be formed by closely winding two thin electrode wires about a cylindrical base and covering with an electrolyte and a membrane.

Claims

1. In an electrode assembly for measuring the concentration of oxygen in a fluid of the type which includes in combination:

an electrolytic medium;

first electrode means having surfaces in contact with said medium;

barrier means for separating said medium from said fluid, and being selectively permeable to said oxygen, and in contact with said medium;

an electrical power source connected for biasing said first electrode means at a potential at which said oxygen in said medium will be consumed at said surfaces of said first electrode means; and

second electrode means having surfaces in contact with said medium and connected to said power source for completing a circuit in which a current from said source can flow through both said electrode means at a level which is a function of such consumption;

said second electrode means and said medium being such that with the combination substantially only said oxygen is electrolytically generable at said second electrode means at said current level, said second electrode means being biased by said power source at a potential at which said oxygen is generable from said medium;

the improvement comprising,

the positioning of said second electrode means with respect to said first electrode means so that said surfaces of said first electrode means are interleaved in side by side relationship with said surfaces of said second electrode means with said surfaces of said electrodes equidistant from said barrier means and the periodicity of said positioning sufficiently small with respect to the thickness and permeability of both said barrier means and said medium to oxygen so that the oxygen generated at said second electrode is consumed at said first electrode without any substantial transfer of oxygen across the interface between said barrier means and said fluids.

2. An electrode assembly as set forth in claim 1 in which said surfaces of said first and second electrode means define a surface which is a flat plane.

3. An electrode assembly as set forth in claim 2 in which said surface of said first and second electrode means are formed by a plurality of thin metal film strips deposited on an insulating flat substrate so as to be closely spaced.

4. An electrode assembly as set forth in claim 1 in which said surfaces of said first and second electrode means define a surface which is cylindrical.

5. An electrode assembly as set forth in claim 1 in which said electrolytic medium is a thin film of liquid electrolyte.

6. An electrode assembly as set forth in claim 1 in which said electrolytic medium is a thin film of solid electrolyte.

7. An electrode assembly as set forth in claim 1 which includes a reference electrode contacting said medium and spaced from said first and second electrode means.

8. An electrode assembly as set forth in claim 1 in which

said electrolytic medium is a solid polymer electrolyte;

and

said first and second electrode means are formed by narrow strips of thin metal film deposited on a flat insulating substrate.

9. In an electrode assembly for measuring the concentration of chlorine in a fluid of the type which includes in combination:

an electrolytic medium;

first electrode means having surfaces in contact with said medium;

barrier means for separating said medium from said fluid, and being selectively permeable to said chlorine, and in contact with said medium;

an electrical power source connected for biasing said first electrode means at a potential at which said chlorine in said medium will be consumed at said surfaces of said first electrode means; and

second electrode means having surfaces in contact with said medium and connected to said power source for completing a circuit in which a current from said source can flow through both said electrode means at a level which is a function of such consumption;

said second electrode means and said medium being such that with the combination substantially only said chlorine is electrolytically generable at said second electrode means at said current level, said second electrode means being biased by said power source at a potential at which said chlorine is generable from said medium;

the improvement comprising,

The positioning of said second electrode means with respect to said first electrode means so that said surfaces of said first electrode means are interleaved in side by side relationship with said surfaces of said second electrode means with said surfaces of said electrodes equidistant from said barrier means and the periodicity of said positioning sufficiently small with respect to the thickness and permeability of both said barrier means and said medium to chlorine so that the chlorine generated at said second electrode is consumed at said first electrode without any substantial transfer of chlorine across the interface between said barrier means and said fluid.

10. The method of measuring the concentration of an electrochemically active species in a fluid comprising the steps of:

immersing in said fluid an electrode assembly including;

an electrolytic medium from which only said species is electrolytically generable,

barrier means selectively permeable to said species,

first electrode means of material electro-chemically inert to both said medium and said species and having surfaces in contact with said medium,

second electrode means of material electro-chemically inert to both said medium and said species, said second electrode means having surfaces in contact with said medium,

means for supporting said first and second electrode means to position their respective surfaces in contact with said medium in an interleaved side by side relationship with said surfaces equidistant from said barrier means and positioned so that the periodicity of the spacing of said electrode surfaces is sufficiently small with respect to the thickness and species permeability of both said barrier means and said medium so that the species generated at the surfaces of said second electrode is consumed at the adjacent surfaces of said first electrode without any substantial transfer of said species across the interface between said barrier means and said fluid, and

means connecting said first and second electrodes to a power source operable to bias said first and second electrodes at potentials to produce a current between said electrodes such that said species will be generated at said second electrode and consumed at said first electrode in quantity dependent upon the tendency of said species to establish an equilibrium condition across said barrier means between the respective concentrations of said species in said medium and said fluid; and

measuring said current flow as an indication of said species concentration in said fluid.