Apparatus for quantitative determination of chemical oxidizing or reducing agents in a fluid environment

• US 5,346,605 A
• Filed: 06/29/1993
• Issued: 09/13/1994
• Est. Priority Date: 08/24/1992
• Status: Expired due to Fees

• Current Assignee: The Dow Chemical Company (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Wolcott, Duane K., Noding, Stephen A.
• Primary Examiner(s): Tung, T.
• Application Number:
  US08/084,786
• Time in Patent Office: 441 Days
• Field of Search: 204/153.13, 204/183.17, 204/412, 204/415, 204/431, 204/432, 204/414, 204/430
• US Class Current: 204/412
• CPC Class Codes: G01N 27/40 Semi-permeable membranes or partitions
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 27/4162 investigating the composition of gases, by the influence exerted on ionic conductivity in a liquid conductometry in general G01N27/06; amperometric gas sensors G01N27/404

Abstract

An apparatus for the quantitative determination of chlorine in a fluid environment, comprising a flat ion exchange membrane-based sensor which utilizes a layer of an electrochemically inert hydrated salt or combination of such salts to provide water for the reduction of such chlorine to chloride ion, and the detection of chlorine by such reduction.

Claims

1. A sensor suited for use in an apparatus for the quantitative determination of chemical oxidizing or reducing agents in a fluid environment, comprising:

a first, sensing electrode for contacting oxidizing or reducing agents in the fluid environment and producing an ionic species therefrom;

a layer of an electrochemically inert hydrated salt or combination of electrochemically inert hydrated salts adjacent the first electrode and through which an oxidizing or reducing agent species must pass to encounter the first electrode;

means for retaining the layer of salt(s) in such position;

a reservoir of an electrolytic solution;

a second electrode in contact with the reservoir of electrolytic solution; and

an ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode, which prevents the ionic species produced at the first electrode from an oxidizing or reducing agent from passing into the reservoir of electrolytic solution.

2. A sensor as defined in claim 1, wherein the fluid environment has a water content corresponding to a relative humidity of about 40 percent or less at temperatures in the range of from about 20 to about 30 degrees Celsius, and wherein when the sensor is used as part of an apparatus for the quantitative determination of chemical oxidizing or reducing agents in such a fluid environment, the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 4000 parts per million.

3. A sensor as defined in claim 2, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 100 parts per million.

4. A sensor as defined in claim 3, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 10 parts per million.

5. A sensor as defined in claim 1, wherein the fluid environment has a water content corresponding to a relative humidity of about 20 percent or less at temperatures in the range of from about 20 to about 30 degrees Celsius, and wherein when the sensor is used as part of an apparatus for the quantitative determination of chemical oxidizing or reducing agents in such a fluid environment, the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 4000 parts per million.

6. A sensor as defined in claim 5, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 100 parts per million.

7. A sensor as defined in claim 6, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 10 parts per million.

8. A sensor as defined in claim 1, wherein the fluid environment has a water content corresponding to a relative humidity of about 10 percent or less at temperatures in the range of from about 20 to about 30 degrees Celsius, and wherein when the sensor is used as part of an apparatus for the quantitative determination of chemical oxidizing or reducing agents in such a fluid environment, the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 4000 parts per million.

9. A sensor as defined in claim 8, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 100 parts per million.

10. A sensor as defined in claim 9, wherein the response of the apparatus is essentially linear for concentrations of an oxidizing or reducing agent species ranging from about 0.1 to about 10 parts per million.

11. A sensor as defined in claim 1, wherein at a chlorine concentration in the fluid environment in the range of from about 5 to about 10 parts per million, the sensor when used as part of an apparatus for the quantitative determination of chlorine in a fluid environment demonstrates a change in response of no more than about 1 percent when the water content of the fluid environment changes to an extent corresponding to a 5 percent change in relative humidity at temperatures in the range of from about 20 to about 30 degrees Celsius.

12. A sensor as defined in claim 11, wherein at a chlorine concentration in the fluid environment in the range of from about 5 to about 10 parts per million, the sensor when used as part of an apparatus for the quantitative determination of chlorine in a fluid environment demonstrates a change in response of no more than about 1 percent when the water content of the fluid environment changes to an extent corresponding to a 50 percent change in relative humidity at temperatures in the range of from about 20 to about 30 degrees Celsius.

13. A sensor as defined in claim 1, wherein the ion-exchange membrane has been preconditioned by placing the membrane in an electrolyte solution of hydrogen ion and a single cation moiety selected from the group consisting of alkali metal cations and alkali earth metal cations, and then passing an electrical current through the electrolyte solution and membrane.

14. A sensor as defined in claim 1, wherein the electrolytic solution is in the form of a gel.

15. A sensor as defined in claim 1, wherein the first electrode is in the form of a flat wire mesh positioned against the ion-exchange membrane, with the layer of hydrated salt(s) on an opposite side of the flat wire mesh first electrode from the ion-exchange membrane.

16. A sensor as defined in claim 15, wherein the sensor further comprises a protective semipermeable, hydrophobic film layer on a side of the layer of hydrated salt(s) opposite the first wire mesh electrode which permits water vapor and the oxidizing or reducing agent species to pass therethrough.

17. A sensor suited for use in a apparatus for the quantitative determination of chemical oxidizing or reducing agents in a fluid environment, comprising:

a first, sensing electrode for contacting oxidizing or reducing agents in a fluid environment and producing an ionic species therefrom;

a reservoir of an electrolytic solution;

a second, reference electrode in contact with the reservoir of electrolytic solution;

a layer of an electrochemically inert hydrated salt or salts positioned adjacent the first electrode and through which an oxidizing or reducing agent species must pass to encounter the first electrode;

means for retaining the layer of salt(s) in such position;

a third, externally-driven electrode which in operation is in contact with the fluid environment and which supplies current to the sensing electrode that would otherwise be supplied by the corrosion in the electrolytic solution of the second electrode;

a first ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode, which prevents the ionic species produced at the first electrode from an oxidizing or reducing agent from passing into the reservoir of electrolytic solution; and

a second ion-exchange membrane separating the electrolytic solution and second electrode from the third electrode, wherein the second ion-exchange membrane admits passage of oppositely-charged ionic species from those admitted by the first ion-exchange membrane.

18. An apparatus for the quantitative determination of chemical oxidizing or reducing agents in a fluid environment, comprising:

a sensor which includes;

a first, sensing electrode for contacting oxidizing or reducing agents in the fluid environment and producing an ionic species therefrom;

a layer of an electrochemically inert hydrated salt or combination of electrochemically inert hydrated salts adjacent the first electrode and through which an oxidizing or reducing agent species must pass to encounter the first electrode;

means for retaining the layer of salt(s) in such position;

a reservoir of an electrolytic solution;

a second electrode in contact with the reservoir of electrolytic solution; and

an ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode, which prevents the ionic species produced at the first electrode from an oxidizing or reducing agent from passing into the reservoir of electrolytic solution;

means for placing the first and second electrodes in electrical contact; and

means for measuring a flow of electrical current generated between the electrodes.

19. An apparatus for the quantitative determination of chemical oxidizing or reducing agents in a fluid environment, comprising:

a sensor which includes;

a first, sensing electrode for contacting oxidizing or reducing agents in a fluid environment and producing an ionic species therefrom;

a reservoir of an electrolytic solution;

a second, reference electrode in contact with the reservoir of electrolytic solution;

a layer of an electrochemically inert hydrated salt or salts positioned adjacent the first electrode and through which an oxidizing or reducing agent species must pass to encounter the first electrode;

means for retaining the layer of salt(s) in such position;

a third, externally-driven electrode which in operation is in contact with the fluid environment and which supplies current to the sensing electrode that would otherwise be supplied by the corrosion in the electrolytic solution of the second electrode;

a first ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode, which prevents the ionic species produced at the first electrode from an oxidizing or reducing agent from passing into the reservoir of electrolytic solution; and

a second ion-exchange membrane separating the electrolytic solution and second electrode from the third electrode, wherein the second ion-exchange membrane admits passage of oppositely-charged ionic species from those admitted by the first ion-exchange membrane;

an applied voltage generator;

a current booster amplifier for driving current through the sensor via the third electrode to produce a controlled potential between the first and second electrodes;

a feedback loop to adjust the drive current through the third electrode so as to maintain the controlled potential, said feedback loop offering high impedance to current flow through the reference electrode;

a current to voltage convertor converting current flow through the sensor to voltage; and

means for zero-adjusting the converted voltage to offset the voltage attributable to the current produced via said applied voltage generator.

20. A chlorine sensor suited for use in an apparatus for the quantitative determination of chlorine in a fluid environment, comprising:

a first, platinum flat wire mesh sensing electrode for contacting chlorine in the fluid environment and reducing chlorine to chloride ions;

a layer of an electrochemically inert hydrated lithium salt or combination of electrochemically inert hydrated lithium salts adjacent the first electrode and through which the chlorine must pass to encounter the first electrode;

a protective semipermeable, hydrophobic film layer positioned against the layer of salt(s) for holding the layer of salt(s) in such position;

a reservoir of a gelatinous electrolytic solution of lithium chloride and water;

a second, silver electrode in contact with the reservoir of electrolytic solution; and

a cation ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode.

21. A chlorine sensor suited for use in an apparatus for the quantitative determination of chlorine in a fluid environment, comprising:

a first, platinum flat wire mesh sensing electrode for contacting the chlorine in the fluid environment and reducing chlorine to chloride ions;

a reservoir of a gelatinous electrolytic solution of lithium chloride and water;

a second, silver reference electrode in contact with the reservoir of electrolytic solution;

a layer of an electrochemically inert hydrated lithium salt or lithium salts positioned adjacent the first electrode and through which chlorine must pass to encounter the first electrode;

a protective semipermeable, hydrophobic film layer positioned against the layer of salt(s) for holding the layer of salt(s) in such position;

a third, externally-driven platinum flat wire mesh electrode which in operation is in contact with the fluid environment and which supplies current to the sensing electrode that would otherwise be supplied by the corrosion in the electrolytic solution of the second electrode;

a cation ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode;

an anion ion-exchange membrane separating the electrolytic solution and second electrode from the third electrode; and

a protective semipermeable, hydrophobic film layer positioned over the third electrode.

22. An apparatus for the quantitative determination of chlorine in a fluid environment, comprising:

a sensor which includes;

a first, platinum flat wire mesh sensing electrode for contacting chlorine in the fluid environment and reducing chlorine to chloride ions;

a layer of an electrochemically inert hydrated lithium salt or combination of electrochemically inert hydrated lithium salts adjacent the first electrode and through which the chlorine must pass to encounter the first electrode;

a protective semipermeable, hydrophobic film layer positioned against the layer of salt(s) for holding the layer of salt(s) in such position;

a reservoir of a gelatinous electrolytic solution of lithium chloride and water;

a second, silver electrode in contact with the reservoir of electrolytic solution; and

a cation ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode;

means for placing the first and second electrodes in electrical contact; and

means for measuring a flow of electrical current generated between the electrodes.

23. An apparatus for the quantitative determination of chlorine in a fluid environment, comprising:

a sensor which includes;

a first, platinum flat wire mesh sensing electrode for contacting the chlorine in the fluid environment and reducing chlorine to chloride ions;

a reservoir of a gelatinous electrolytic solution of lithium chloride and water;

a second, silver reference electrode in contact with the reservoir of electrolytic solution;

a layer of an electrochemically inert hydrated lithium salt or lithium salts positioned adjacent the first electrode and through which chlorine must pass to encounter the first electrode;

a protective semipermeable, hydrophobic film layer positioned against the layer of salt(s) for holding the layer of salt(s) in such position;

a third, externally-driven platinum flat wire mesh electrode which in operation is in contact with the fluid environment and which supplies current to the sensing electrode that would otherwise be supplied by the corrosion in the electrolytic solution of the second electrode;

a cation ion-exchange membrane separating the electrolytic solution and second electrode from the first electrode;

an anion ion-exchange membrane separating the electrolytic solution and second electrode from the third electrode; and

a protective semipermeable, hydrophobic film layer positioned over the third electrode;

an applied voltage generator;

a current booster amplifier for driving current through the sensor via the third electrode to produce a controlled potential between the first and second electrodes;

a feedback loop to adjust the drive current through the third electrode so as to maintain the controlled potential, said feedback loop offering high impedance to current flow through the reference electrode;

a current to voltage convertor converting current flow through the sensor to voltage; and

means for zero-adjusting the converted voltage to offset the voltage attributable to the current produced via said applied voltage generator.