Oxidizable species as an internal reference in control solutions for biosensors

A method of distinguishing a control solution from a biological sample during operation of an electrochemical sensor measuring the amount of an analyte in said control solution and in said biological 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, said internal reference compound being added in an amount relative to a predetermined amount of analyte in said control solution sufficient to indicate the presence of said internal reference compound in the control solution;
• (b) introducing said control solution containing said internal reference compound and said predetermined amount of said analyte to an electrochemical sensor, said sensor having working and reference electrodes and a reaction layer containing reagents for oxidizing said analyte;
• (c) at least once applying a potential to said electrodes of 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=ihigh volt/ilow volt
• where:
• ihigh volt is the current measured in (c)
• ilow 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 the internal reference compound from the predetermined amount of analyte;
• and
• (g) determining that a biological sample is present when the Differential Index of (e) is about 1.