Patent ID: 8002965

Claim:
A method of distinguishing a control solution from a sample during operation of an electrochemical sensor measuring the amount of an analyte in said control solution and in said sample, the method comprising the acts of: (a) adding to said control solution an internal reference compound, said compound being adapted to be electrochemically oxidized at a potential higher than the potential needed to measure the oxidation of said analyte; (b) introducing said control solution containing said internal reference compound and a predetermined amount of said analyte to said electrochemical sensor, said sensor having working and counter electrodes and a reagent; (c) at least once applying a potential to said electrochemical sensor sufficient to oxidize said internal reference compound and said analyte, and measuring the resulting electrical current; (d) at least once applying a potential to said electrochemical sensor lower than the potential of (c), said potential being sufficient to measure oxidation of said analyte and not sufficient to oxidize said internal reference compound, and measuring the resulting electrical current; (e) calculating a Differential Index (DI) defined as DI=i high volt /i low volt where: i high volt is the current measured in (c) i low volt is the current measured in (d) (f) determining that a control solution is present when the Differential Index of (e) is sufficiently greater than 1 to distinguish said internal reference compound from said predetermined amount of analyte; and (g) determining that a sample is present when the Differential Index of (e) is about 1; wherein the potential of (d) is applied before the potential of (c).