Method and apparatus for detection of abnormal traces during electrochemical analyte detection
View Patent ↗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.
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 =[k 1 ×t mob ×CottrellSlope m ]+[k 2 ×t mob n ]+[k 3 ×t mob n ×CottrellSlope m ]+k 4
where k 1 -k 4 are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I 2 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 =[k 1 ×t mob ×CottrellSlope m ]+[k 2 ×t mob n ]+[k 3 ×t mob n ×CottrellSlope m ]+k 4
where k 1 -k 4 are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I 2 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 =[k 1 ×t mob ×CottrellSlope m ]+[k 2 ×t mob n ]+[k 3 ×t mob n ×CottrellSlope m ]+k 4
where k 1 -k 4 are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I 2 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 =[k 1 ×t mob ×CottrellSlope m ]+[k 2 ×t mob n ]+[k 3 ×t mob n ×CottrellSlope m ]+k 4
where k 1 -k 4 are empirically determined constants, and the CottrellSlope is the square root of the slope of 1/I 2 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.