Methods and apparatus for analyzing a sample in the presence of interferents
View Patent ↗Disclosed herein are methods and apparatus for determining analyte concentration in a rapid and accurate manner. The methods include depositing a physiological sample in an electrochemical cell and finding a first and second current transient. Peak current values are obtained from the first and second peak current values and used to reduce the influence of interferents in a current value. Based on this “corrected” current value, an accurate analyte concentration can be determined.
1. A method for reducing the effect of interferent in a test for analyte concentration, comprising:
(a) introducing a physiological sample into an electrochemical cell, the electrochemical cell comprising:
(i) first and second electrodes in a spaced apart relationship; and
(ii) a first reagent;
(b) applying a first test potential between said first and second electrodes, the first test potential having a first polarity and measuring cell current to obtain a first peak current value;
(c) applying a second test potential between said first and second electrodes, the second test potential having a second polarity, and measuring cell current to obtain a second peak current value;
(d) calculating an interference correction factor based on the first and second peak current values, wherein the interference correction factor can be used in a glucose concentration calculation to reduce the influence of chemical interferent compounds that will generate an interferent current by an oxidation or reduction reaction.
2. The method of claim 1 , wherein the step (c) further includes measuring cell current as a function of time to obtain a second current transient and calculating a first current value based on the second current transient.
3. The method of claim 2 , further comprising the step of calculating a corrected first current value by removing an interferent current value from the first current value.
4. The method of claim 3 , wherein the step of calculating a corrected first current value includes multiplying the first current value by an interferent correction equation, wherein the interferent correction equation is
{
i
pb
-
2
i
pa
+
i
ss
i
pb
+
i
ss
}
where i pb is the first peak current value, i pa is the second peak current value, and i ss is a steady-state current value.
5. The method of claim 4 , wherein the method further includes the steps of calculating a second current value based on the second current transient and measuring cell current as a function of time in step (b) to obtain a first current transient and calculating a third current value based on the first current transient.
6. The method of claim 5 , further comprising the step of calculating an analyte concentration based upon an equation
[
C
]
=
(
i
2
i
3
)
p
×
(
α
×
i
4
-
Z
)
where [C] is an analyte concentration, i 4 is the first correct current value, i 2 is the second current value, i 3 is the third current value, and a, p, and Z are calibration factors.
7. The method according to claim 1 , wherein the first reagent layer is disposed on the first electrode.
8. The method according to claim 7 , wherein the first polarity is negative with respect to the second electrode and the second polarity is positive with respect to the second electrode.
9. The method according to claim 8 , wherein a second reagent layer is disposed on the second electrode, wherein the second reagent layer comprises a redox mediator and is substantially free of the enzyme, and the redox mediator is capable of oxidizing an interferent present in the physiological sample.
10. The method of claim 1 , wherein step (c) further includes measuring cell current as a function of time to obtain a second current transient.
11. The method of claim 1 , wherein an analyte concentration is calculated based upon an equation
[
C
]
=
(
i
ss
i
pp
)
p
×
(
C
o
{
i
pb
-
2
i
pa
+
i
ss
i
pb
+
i
ss
}
-
Z
)
where [C] is an analyte concentration, i pp is a current value derived from the second current transient, C G is an estimated glucose concentration, i pa is the first peak current value, i pb is the second peak current value, and i SS is a steady state current value and Z is a calibration factor.
12. The method of claim 11 , wherein the term i pp is an average current over a short period of time near the end of the second current transient.
13. A method for reducing the effect of interferent in a test for analyte concentration, comprising:
(a) introducing a physiological sample into an electrochemical cell, the electrochemical cell comprising:
(i) a first reagent; and
(ii) two or more electrodes, the two or more electrodes consisting of a single working electrode and one or more other electrodes in a spaced apart relationship;
(b) applying a first test potential between the single working electrode and the one or more other electrodes, the first test potential having a first polarity, and measuring cell current to obtain a first peak current value;
(c) applying a second test potential between the single working electrode and the one or more other electrodes, the second test potential having a second polarity, and measuring cell current to obtain a second peak current value;
(d) calculating an interference correction factor based on the first and second peak current values, wherein the interference correction factor can be used in a glucose concentration calculation to reduce the influence of chemical interferent compounds that will generate an interferent current by an oxidation or reduction reaction.
14. The method of claim 13 , wherein the two or more electrodes consist of a single working electrode and a single reference electrode.