Method and apparatus for detection of abnormal traces during electrochemical analyte detection

• US 7,344,626 B2
• Filed: 04/15/2005
• Issued: 03/18/2008
• Est. Priority Date: 04/15/2005
• 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: Harding, Ian, Williams, Richard
• Primary Examiner(s): Gilliam; Barbara L.
• Assistant Examiner(s): Dinh; Bach
• Application Number:
  US10/907,818
• Publication Number:
  US 20060231425A1
• Time in Patent Office: 1,068 Days
• Field of Search: 204/401, 20440301-40315
• US Class Current: 204/403.01
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: G01N 27/3273 Devices therefor, e.g. test element readers, circuitry details not specific to biochemical electrodes G01N33/4875
• CPC Class Codes: G01N 33/5438 Electrodes

Abstract

Detection of abnormal signal traces in electrochemical measurements generated using an electrochemical test strip to which a potential is applied allows for an indication of an erroneous analyte determination. The current trace has an expected shape in which a peak current is observed a time t_peak after which there is a decrease in current. To detect abnormal signal traces, the time t_peak is determined experimentally and compared with an expected value, t′_peak, and if the difference between the two values to over a predetermined threshold, an error message is provided to the user instead of a test result. The value of t′_peak is determined as a function of a mobility term that is determined during a potentiometry phase following the amperometric measurements.

Claims

1. A method for determination of an analyte in a sample comprising the steps of:

(a) introducing the sample to an electrochemical test strip having working and counter electrodes;

(b) applying a potential difference, V_app, between the electrodes of the test strip and observing a current signal sufficient to provide a determination of analyte in the sample;

(c) determining a time t_peak, said time occurring at a maximum in the current at the point of changeover when sufficient material is available at the counter electrode to balance the consumption of analyte at the working electrode;

(d) switching off the applied potential at time t_switch

(e) determining a time, t_mob, wherein t_mob is the time after the applied potential is switched off, that it takes for the potential between the electrodes to decay to a predetermined value,

(f) calculating an expected value of t_peak, t′

_peak, where t′

_peak is a function of t_mob, and

(g) comparing the absolute value of t_peak−

t′

_peak to a predetermined threshold value, rejecting the test if the absolute value of t_peak−

t′

_peak is greater than the threshold value.

2. The method of claim 1, wherein t′

_peak is given by the equation;

t′

_peak=[k₁×

t_mob×

CottrellSlope^m]+[k₂×

t_mobⁿ]+[k₃×

t_mobⁿ×

CottrellSlope^m]+k₄

where k₁-k₄ are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I² versus t in the Cottrell decay region of the current curve, and n and m are experimental positive or negative integer or fractional numbers.

3. The method of claim 2, wherein n is ½

and m is −

1.

4. A meter for receiving an electrochemical test strip having working and counter electrodes and providing a determination of an analyte in a sample applied to the electrochemical test strip when received in the meter, said meter comprising

(a) a housing having a slot for receiving an electrochemical test strip;

(b) communications means for receiving input from and communicating a result to a user; and

(c) means for applying a potential and to determine analyte concentration from an observed current,

(d) means determining a time t_peak, said time occurring at a maximum in the current at the point of changeover when sufficient material is available at the counter electrode to balance the consumption of analyte at the working electrode;

(e) means for switching off the applied potential at time t_switch, and determining a time, t_mob, wherein t_mob is the time after the applied potential is switched off, that it takes for the potential between the electrodes to decay to a pre-determined value,

(f) means for calculating an expected value of t_peak, t′

_peak, where t′

_peak is a function of t_mob, comparing the absolute value of t_peak−

t′

_peak to a predetermined threshold value, and generating an error message if the absolute value of t_peak−

t′

_peak is greater than the threshold value.

5. The meter of claim 4, wherein t′

_peak is given by the equation;

t′

_peak=[k₁×

t_mob×

CottrellSlope^m]+[k₂×

t_mobⁿ]+[k₃×

t_mobⁿ×

CottrellSlope^m]+k₄

where k₁-k₄ are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I² versus t in the Cottrell decay region of the current curve, and n and m are experimental positive or negative integer or fractional numbers.

6. The meter of claim 5, wherein n is ½

and m is −

1.

7. A measurement system comprising a meter in accordance with claim 4 and an electrochemical test strip received within the housing.

8. The measurement system of claim 7, wherein the electrochemical test strip is for measurement of glucose.

9. The measurement system of claim 8, wherein t′

_peak is given by the equation;

t′

_peak=[k₁×

t_mob×

CottrellSlope^m]+[k₂×

t_mobⁿ]+[k₃×

t_mobⁿ×

CottrellSlope^m]+k₄

where k₁-k₄ are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I² versus t in the Cottrell decay region of the current curve, and n and m are experimental positive or negative integer or fractional numbers.

10. The measurement system of claim 9, wherein n is ½

and m is −

1.

11. The measurement system of claim 7, wherein t′

_peak is given by the equation;

t′

_peak=[k₁×

t_mob×

CottrellSlope^m]+[k₂×

t_mobⁿ]+[k₃×

t_mobⁿ×

CottrellSlope^m]+k₄

where k₁-k₄ are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I² versus t in the Cottrell decay region of the current curve, and n and m are experimental positive or negative integer or fractional numbers.

12. The measurement system of claim 11, wherein n is ½

and m is −

1.