Electrochemical determination of analytes

• US 20080093230A1
• Filed: 10/18/2007
• Published: 04/24/2008
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Original Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Inventors: Diamond, Steven, Harding, Ian, Williams, Richard, Iyengar, Sridhar
• Granted Patent: US 7,771,583 B2
• Time in Patent Office: Days
• US Class Current: 205/792
• CPC Class Codes: G01N 27/3274 Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771

Abstract

Determination of an analyte with increased accuracy is achieved by electrochemically determining an initial analyte concentration, performing a plurality of amperometric/potentiometric switching cycles, observing a characteristic of the signal during each of the plurality of switching cycles, determining an averaged value for the characteristic of the signal, and correcting the initial measurement value to arrive at a final measurement value of analyte concentration or rejecting the initial measurement value depending on the averaged value of the characteristic of the signal. The characteristic of the signal that is observed is not per se indicative of the amount of analyte present in a sample. Rather, it is a characteristic of the signal that reflects the quality of the electrodes, the extent of fill of the electrochemical cell or characteristics of the sample other than analyte concentration such as oxygen levels or hematocrit.

Claims

1. A method for determination of an analyte with increased accuracy comprising the steps of:

(a) electrochemically determining an initial measurement value of analyte concentration in a liquid sample disposed between a working and a counter electrode,

(b) performing a plurality of amperometric/potentiometric switching cycles bet ween the working and counter electrodes,

(c) observing a characteristic of the signal during each of the plurality of switching cycles,

(d) determining an averaged value for the characteristic of the signal, and

(e) correcting the initial measurement value to arrive at a final measurement value of analyte concentration or rejecting the initial measurement value depending on the averaged value of the characteristic of the signal.

2. The method of claim 1, wherein the characteristic of the signal that is observed reflects the quality of the electrodes, the extent of fill of the electrochemical cell or a characteristic of the sample other than analyte concentration.

3. The method of claim 2, wherein the characteristic of the signal that is observed is series electrode resistance.

4. The method of claim 3, wherein each switching cycle comprising the steps of switching off the applied potential at time t_switch and determining the magnitude, V_drop, of the immediate voltage drop, and then switching the potential back on to prepare for the next switching cycle, and wherein the averaged value of V_drop is determined according to equation

5. The method of claim 3, wherein each switching cycle comprising the steps of switching off the applied potential at time t_switch and determining the magnitude, V_drop, of the immediate voltage drop, and then switching the potential back on to prepare for the next switching cycle, and determining a current, I_pre-switch prior to switching off the application potential or initiation of the switching cycles, and then determining an average value of track resistance according to the equation:

6. The method of claim 5, wherein I_pre-switch is a plateau current.

7. The method of claim 2, wherein the characteristic of the signal that is observed is double-layer capacitance as an indication of the extent of fill of the electrochemical cell.

8. The method of claim 7, wherein the plurality of switching cycles include the steps or

(i) applying potential and measuring a first current value

(ii) switching off potential, observe decay of potential,

(iii) determining first double layer capacitance from current and observation from potential decay;

(iv) reapplying potential to observe a second to nth current value

(v) switching off potential and observing decay of potential,

(vi) determining a second to nth double layer capacitance from first or second to nth current and second to nth observation of potential decay;

(vii) determining an average value of double layer capacitance.

9. The method of claim 7, wherein the plurality of switching cycles include the steps of

(i) applying potential and measuring a first current value

(ii) switching off potential, and observing decay of potential,

(iii) reapplying the potential to observe a first charging Current transient and determining a first double layer capacitance from the first charging current transient and the potential decay;

(iv) switching off potential and observing second to nth decay of potential, and then reapplying the potential to observe a second to nth charging current transient and determining a second to nth double layer capacitance from the second to nth charging current transient and the second to nth potential decay; and

(vii) determining an average value of double layer capacitance.

10. The method of claim 2, wherein the characteristic of the signal that is observed reflects oxygen levels in the sample.

11. The method of claim 1, wherein the initial determination of analyte concentration is made before the plurality of amperometric/potentiometric switching cycles.

12. The method of claim 1, wherein the characteristic of the signal that is observed reflects the quality of the electrodes, the extent of fill of the electrochemical call or a characteristic of the sample other than analyte concentration.

13. The method of claim 12, wherein the characteristic of the signal that is observed is series electrode resistance.

14. The method of claim 13, wherein each switching cycle comprising the steps of switching off the applied potential at time t_switch and determining the magnitude, V_drop, of the immediate voltage drop, and then switching the potential back on to prepare for the next switching cycle, aid wherein the averaged value of V_drop is determined according to equation

15. The method of claim 13, wherein each switching cycle comprising the steps of switching off the applied potential at time t_switch and determining the magnitude, V_drop, or the immediate voltage drop, and then switching the potential back on to prepare for the next switching cycle, and determining a current, I_pre-switch prior to switching off the application potential or initiation of the switching cycles, and then determining an average value of track resistance according to the equation:

16. The method of claim 15, wherein I_pre-switch is a plateau current.

17. The method of claim 12, wherein the characteristic of the signal that is observed is double-layer capacitance as an indication of the extent of fill of the electrochemical cell.

18. The method of claim 17, wherein the plurality of switching cycles include the steps of

(i) applying potential and measuring a first current value

(ii) switching off potential and observing decay of potential,

(iii) determining first double layer capacitance from the first current value and the observed potential decay;

(iv) reapplying potential to observe a second to nth current value

(v) switching off potential and observing decay of potential,

(vi) determining a second to nth double layer capacitance from first or second to nth current and second to nth observation of potential decay;

(vii) determining an average value of double layer capacitance.

19. The method of claim 17, wherein the plurality of switching cycles include the steps of

(i) applying potential and measuring a first current value

(ii) switching off potential, and observing decay of potential,

(iii) reapplying the potential to observe a first charging current transient and determining a first double layer capacitance from the first charging current transient and the potential decay;

(iv) switching off potential and observing second to nth decay of potential, and then reapplying the potential to observe a second to nth charging current transient and determining a second to nth double layer capacitance from the second to nth charging current transient and the second to nth potential decay; and

(vii) determining an average value of double layer capacitance.

20. The method of claim 10, wherein the characteristic of the signal that is observed reflects oxygen levels or hematocrit in the sample.

21. The method of claim 1, in which the averaged value is a weighted average.