Method for detecting the fouling of a membrane covered electrochemical cell

• US 4,168,220 A
• Filed: 07/10/1978
• Issued: 09/18/1979
• Est. Priority Date: 07/10/1978
• Status: Expired due to Term

• Current Assignee: Leeds & Northrup Co.
• Original Assignee: Leeds & Northrup Co.
• Inventors: Taylor, Robert M., McAdam, Will
• Primary Examiner(s): Tung, T.
• Application Number:
  US05/923,502
• Time in Patent Office: 435 Days
• Field of Search: 204/1 P, 204/195 P
• US Class Current: 205/782.5
• CPC Class Codes: G01N 27/48 using polarography, i.e. measuring changes in current under a slowly-varying voltage

Abstract

In a polarographic cell of the type which avoids depletion of the species being measured in the sample, the fouling of the membrane covering of the cell is detected by utilizing an electrode which can be substituted for that electrode from which the species being measured is electrochemically generated. That electrode is spaced remotely from the closely spaced anode and cathode so that when it is substituted depletion of the species being measured occurs outside the membrane. By comparing the current output from the cell when it is operating in its normal mode with the output when it is operating with the substitute electrode, as by dividing one value by the other, the degree of fouling of the membrane covering the cell is determined.

Claims

1. A method for determining the degree of membrane fouling of a Ross-type cell being used to measure the concentration of an electrochemically active species in a fluid when said cell includes, in close-spaced relationship, a first electrode at which the species is electrochemically consumed, a second electrode at which the species is electrochemically generable, and another electrode positioned remotely from said first electrode but in the same electrolyte with said first and second electrodes, all electrodes being on the side of the membrane away from the fluid, comprising the steps of:

measuring the current output from said cell when said cell is operating in the Ross mode;

substituting said another electrode for said second electrode so as to cause said Ross-type cell to operate in the Clark mode;

measuring the current output from said cell when said Ross-type cell is operating in the Clark mode; and

comparing said measurements to obtain an indication of the degree of fouling.

2. The method of claim 1 in which said comparison is made by dividing one measurement by the other.

3. A method for determining the degree of membrane fouling of an electrode assembly for measuring the concentration of a specific electrochemically active species in a fluid wherein the electrode assembly includes:

an electrolytic medium;

first electrode means of a material electrochemically inert to both said electrolyte and said species and in contact with said medium;

a membrane for separating said medium from said fluid, said membrane being selectively permeable to said species and in contact with said medium;

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

second electrode means of a material electrochemically inert to both said medium and said species, said second electrode means being 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 medium being one from which substantially only said species 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 species in generable from said medium; and

said first electrode means being so positioned with respect to second electrode means and said membrane that said species as generated at said second electrode means is available for consumption at said first electrode means in quantity dependent upon a tendency of said species to establish an equilibrium condition across said membrane between the concentration of said species respectively in said electrolyte and in said fluid; and

third electrode means of a material electrochemically inert in both said medium and said species and positioned in said medium remotely from said first electrode so that when said species is generated by said third electrode it is not available for consumption by said first electrode;

comprising the steps of;

measuring the current through said first and second electrode means;

substituting said third electrode for said second electrode in said circuit;

measuring the current through said first and third electrode means; and

comparing the current through said first and second electrode means with the current through said first and third electrode means to obtain an indication of the degree of fouling.

4. A method for determining the degree of membrane fouling of an electrode assembly for measuring the concentration of a specific electrochemically active species in a fluid wherein the electrode assembly includes:

an electrolytic medium;

first and second electrode means of a material electrochemically inert to both said electrolyte and said species and in contact with said medium;

third and fourth electrode means positioned in said medium remotely from said first electrode so that any species generated by said third electrode is not available for consumption by said first electrode;

a membrane for separating said medium from said fluid, said membrane being selectively permeable to said species; and

in contact with said medium;

an electrical power source connected so as to maintain the current flow between the first and second electrodes at a value such that the potential of the first electrode means with respect to the fourth electrode is maintained equal to a predetermined value such that said species in said medium will be consumed at said first electrode means and said current will be at a level which is a function of said consumption;

said medium being one from which substantially only said species is electrolytically generable at said second electrode means at said current level; and

said first electrode means being so positioned with respect to said second electrode means and said membrane that said species as generated at said second electrode means is available for consumption at said first electrode means in quantity dependent upon a tendency of said species to establish an equilibrium condition across said membrane between the concentration of said species respectively in said medium and in said fluid;

comprising the steps of;

measuring the current through said first and second electrode means;

substituting said third electrode for said second electrode in said circuit;

measuring the current through said first and third electrode means; and

comparing the current through said first and second electrode means with said current through said first and third electrode means to obtain an indication of the degree of fouling.

5. A method for determining the degree of membrane fouling of an electrode assembly for measuring the concentration of a specific electrochemically active species in a fluid wherein the electrode assembly includes:

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

a membrane selectively permeable to said species;

first and second electrode means of material electrochemically inert to both said medium and said species and 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 membrane and positioned 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 membrane 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 membrane between the respective concentrations of said species in said medium and said fluid; and

third electrode means positioned in said medium remotely from said first electrode so that any of said species generated at said third electrode is not available for consumption at said first electrode;

comprising the steps of;

measuring the current through said first and second electrode means;

substituting said third electrode for said second electrode in said circuit;

measuring the current through said first and third electrode means; and

comparing the current through said first and second electrode means with said current through said first and third electrode means to obtain an indication of the degree of fouling.

6. The method as set forth in claim 5 in which said comparison is made by dividing one measurement by the other.