Method for determining analyte concentration in a sample
A method for determining a concentration of an analyte in a fluidic sample is described. A sample is applied to a biosensor including an electrochemical cell having electrodes. A predetermined voltage waveform is applied during at least first and second time intervals. At least first and second current values are measured during the first and second time intervals, respectively. A turning point time is determined during the first time interval at which the measured first current values transition from a first to a second profile. The concentration of analyte in the sample is calculated based on determined turning point time and at least one measured current value. In another example, a physical characteristic of the sample is estimated based on measured current values. The concentration is calculated using a first or second model if the estimated physical characteristic of the sample is in a first or second range, respectively.
1. A method for determining a concentration of an analyte in a fluidic sample, the method comprising:
applying the fluidic sample to a biosensor, the biosensor comprising an electrochemical cell having electrodes;
applying a voltage waveform comprising at least a first predetermined voltage applied during a first time interval and a second predetermined voltage different from the first predetermined voltage applied during a second time interval;
measuring at least first current values during the first time interval and second current values during the second time interval;
determining a turning point time during the first time interval at which the measured first current values transition from a first profile to a second profile; and
estimating a physical characteristic of the sample based on the turning point time, the first measured current values and the second measured current values;
if the estimated physical characteristic of the sample is in a first range, calculating the concentration of the analyte in the sample using a first model based on the first measured current values and the second measured current values; and
if the estimated physical characteristic of the sample is in a second range, calculating the concentration of the analyte in the sample using a second model based on the determined turning point time, the first measured current values and second measured current values.
2. The method of claim 1 , wherein the first model comprises first coefficients and the second model comprises second coefficients, and the first coefficients and the second coefficients are determined by linear optimization.
3. The method of claim 1 , wherein the physical characteristic is the hematocrit level of the fluidic sample.
4. The method of claim 2 , wherein the voltage waveform further comprises a third predetermined voltage applied during a third time interval, the method further comprising measuring third current values during the third time interval.
5. The method of claim 4 , wherein calculating the analyte concentration using the first model comprises using an equation of the form G basic 1 =(a 1 ·|i 2corr |−z gr 1 ), and calculating the analyte concentration using the second model comprises using an equation of the form:
G basic 2 =( a 2 ·|i 2corr |−z gr 2 ), in which:
G basic 1 is the analyte concentration calculated using the first model (in mg/dL);
a 1 and z gr 1 are first model predetermined coefficients;
G basic 2 is the analyte concentration calculated using the second model (in mg/dL);
a 2 and z gr 2 are second model predetermined coefficients;
i
2
corr
=
+
b
-
c
+
b
·
i
r
(
in
microamperes
)
;
i pc is close to a negative peak of the third current values in the third time interval (in microamperes);
i pb is close to a peak of the second current values in the second time interval (in microamperes);
i ss is a steady state of the third current values in the third time interval;
i r is a sum of at least some of the measured third current values of the third time interval (in microamperes); and
b, c and p are predetermined coefficients.
6. The method of claim 1 , wherein the biosensor comprising the electrochemical cell has at least two electrodes.
7. The method of claim 6 , wherein the at least two electrodes of the electrochemical cell are disposed either cofacially or coplanar relative to one another.
8. The method of claim 7 , wherein the at least two electrodes of the electrochemical cell comprise a bare electrode and an at least partially reagent covered electrode.
9. The method of claim 1 , wherein the measuring of the first and second current values is at a frequency between 50-200 Hz.
10. The method of claim 1 , wherein the measured first current values transition from the first profile to the second profile due to the presence of an interferent in the sample.
11. The method of claim 10 , wherein a current i pb representative of a transition from a first predetermined voltage of the waveform during the first time interval and a second predetermined voltage of the waveform during the second time interval occurs during an initial portion of the second time interval.
12. The method of claim 11 , wherein the turning point time occurs prior to the occurrence of i pb .
13. The method of claim 10 , wherein the interferent comprises uric acid or ascorbic acid.
14. The method of claim 1 , wherein the first profile deviates from a Cottrell profile and the second profile follows a Cottrell profile.