Electrochemical sensor for determining analyte in the presence of interferent

• US 20020027086A1
• Filed: 05/14/2001
• Published: 03/07/2002
• Est. Priority Date: 05/13/2000
• Status: Active Grant

• Current Assignee: Alphasense Limited (Ametek Incorporated)
• Original Assignee: Alphasense Limited (Ametek Incorporated)
• Inventors: Saffell, John R., Dawson, Darryl H., Hitchman, Michael L.
• Granted Patent: US 6,623,619 B2
• Time in Patent Office: Days
• US Class Current: 205/783
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 33/004 for CO, CO2

Abstract

Electrochemical sensor for determining analyte in the presence of interferent, particularly carbon monoxide in the presence of hydrogen. An electrochemical cell is designed so that current flow resulting from reference electrode potential shift caused by interferent cancels out the current flow caused by interferent at the working electrode. Another electrochemical cell corrects for interferent concentration using the potential difference between a reference electrode in contact with interferent and a referent electrode not affected by inteferent.

Claims

1. An electrochemical cell for sensing an analyte in the presence of an interferent, the electrochemical cell comprising a reference electrode and a working electrode connected by a potentiostatic circuit, the analyte reacting at the working electrode giving a first component of current, the interferent undergoing an electrochemical reaction giving a second component of current, the presence at the reference electrode of the interferent leading to a shift in the potential of the reference electrode, wherein the shift in the potential of the reference electrode and the action of the potentiostatic circuit leads to a third component of current, wherein properties of the electrochemical cell which affect the magnitude of the third component of current are selected so that the third component of current acts to partially, completely or over compensate for the second component of current.

2. The electrochemical cell of claim 1 wherein the interferent cohabits with the analyte gas.

3. The electrochemical cell of claim 1 wherein the interferent is generated by the counter electrode.

4. The electrochemical cell of claim 1 wherein the properties of the electrochemical cell which affect the magnitude of the third component of current are one or more of the capacitance of the working electrode, the metal on the reference electrode, the oxidation state of the metal on the reference electrode, the redox couple, capacitance or geometry of the reference electrode.

5. The electrochemical cell of claim 1, being a gas sensor.

6. The electrochemical cell of claim 5 wherein the analyte is carbon monoxide and the interferent is hydrogen.

7. The electrochemical cell of claim 5 wherein the working electrode is a circular gas porous disk.

8. The electrochemical cell of claim 5 wherein the reference electrode is an annulus, coaxial with the working electrode.

9. The electrochemical cell of claim 5 wherein the reference electrode is at least partially exposed to the analyte gas without electrolyte between the electrode and analyte gas.

10. The electrochemical cell of claim 5 wherein the capacitance of the working electrode is at least 1 mF.

11. The electrochemical cell of claim 1 which, in use, makes measurements periodically.

13. The electrochemical cell of claim 12 wherein the interferent cohabits with the analyte gas.

14. The electrochemical cell of claim 12 wherein the interferent is generated by the counter electrode.

15. The electrochemical cell of claim 12 wherein the electrochemical cell is a gas sensor.

16. The electrochemical cell of claim 15 wherein the analyte is carbon monoxide and the interferent is hydrogen.

17. The electrochemical cell of claim 12 wherein the first reference electrode is positioned to come into contact with minimised concentrations of interferent.

18. The electrochemical cell of claim 12 wherein the second reference electrode is at least partially in direct contact with the analyte/interferent without electrolyte between the second reference electrode and analyte/interferent.

20. The method of claim 19 further comprising the step of taking into account interferent which will be produced at the counterelectrode when selecting the properties of the electrochemical cell which affect the magnitude of the third component of current.

21. The method of claim 19 wherein the properties of the electrochemical cell which affect the magnitude of the third component of current and which are selected are one or more of the capacitance of the working electrode, the metal on the reference electrode, the oxidation state of the metal on the reference electrode, the redox couple, capacitance or geometry of the reference electrode.

22. The method of claim 21, for designing a sensor for determining carbon monoxide in the presence of hydrogen.

24. The method of claim 23 wherein a measure of the concentration of the analyte is achieved by scaling and substracting the inverse logarithm of the potential difference between the first and second reference electrodes from the total current measured at the working electrode.

25. The method of claim 23 for measuring the concentration of carbon monoxide in the presence of hydrogen.

12. An electrochemical cell for sensing an analyte in the presence of an interferent, the electrochemical cell comprising a working electrode and a first reference electrode connected by a potentiostatic circuit, the interferent not affecting the reference electrode thus avoiding a shift in the potential of the reference electrode, the analyte reacting at the working electrode giving a first component of current, the interferent undergoing an electrochemical reaction giving a second component of current characterized in that there is further provided a second reference electrode, configured so as to be exposed to the interferent, the interferent causing a shift in the potential of the second reference electrode, the second reference electrode being connected to the first reference electrode by a potentiometric circuit for providing a measure of the potential difference between the first and second reference electrodes, said potential difference between the first and second reference electrodes being used to calculate the second component of current and thereby provide a measure of the concentration of the analyte which has reduced or no dependency on the concentration of the interferent.

19. A method for designing an electrochemical cell for sensing an analyte in the presence of an interferent, the electrochemical cell comprising a reference electrode and a working electrode connected by a potentiostatic circuit, the analyte reacting at the working electrode giving a first component of current, the interferent undergoing an electrochemical reaction giving a second component of current, the presence at the reference electrode of the interferent leading to a shift in the potential of the reference electrode, wherein the shift in the potential of the reference electrode and the action of the potentiostatic circuit leads to a third component of current, the method comprising the steps of:

selecting the properties of the electrochemical cell which affect the magnitude of the third component of current so that the third component of current acts to partially, completely or over compensate for the second component of current.

23. A method for calculating the concentration of an analyte in the presence of an interferent using an electrochemical cell comprising a working electrode and a first reference electrode connected by a potentiostatic circuit and also a second reference electrode, the interferent not affecting the reference electrode thus avoiding a shift in the potential of the reference electrode, the analyte reacting at the working electrode giving a first component of current, the interferent undergoing an electrochemical reaction giving a second component of current, the second reference electrode being configured so as to be exposed to the interferent, the interferent causing a shift in the potential of the second reference electrode, the second reference electrode being connected to the first reference electrode by a potentiometric circuit for providing a measure of the potential difference between the first and second reference electrodes, the method comprising the steps of:

measuring the potential difference between the first and second reference electrodes;

thereby calculating the second component of current; and

thereby providing a measure of the concentration of the analyte which has reduced or no dependency on the concentration of the interferent.

26. Computer software comprising program code which, when loaded onto a computer, causes it to calculate the concentration of an analyte in the presence of an interferent by the method of claim 23.