Oxidizable species as an internal reference in control solutions for biosensors

1. 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).

2. The method of claim 1 , wherein said Differential Index determined in (f) is 1.5 or higher.

3. The method of claim 1 , wherein said analyte is glucose and said sample is whole blood.

4. The method of claim 1 , wherein said internal reference compound is added in an amount proportional to the amount of the analyte present in said control solution.

5. The method of claim 4 , wherein said internal reference compound is added in an amount such that the Differential Index is 1.5 or higher when the amount of the analyte is the maximum used in said control solution.

6. The method of claim 1 , wherein said internal reference compound is an oxidizable organo-metallic compound, coordination compound, or organic amine compound.

7. The method of claim 6 , wherein said internal reference compound is said organic amine compound, said organic amine compound being 3-(N-morpholino) propane sulfonic acid, N-(2-hydroxyethyl)piperazine-N 1 -(2-ethane sulfonic acid), 2-[(2-Hydroxy-1,1-bis(hydroxy methyl)ethylamino]ethane sulfonic acid, 2-Morpholino ethane sulfonic acid, and Bis(2-hydroxyethyl)amino-tris (hydroxymethyl)methane[Bis-Tris], 4-aminobenzonitrile, 4-aminobenzoic acid, or 4-iodoaniline.

8. The method of claim 6 , wherein said internal reference compound is said oxidizable organo-metallic compound, said oxidizable organo-metallic compound being ferrocene or ferrocene derivatives.

9. The method of claim 6 , wherein said internal reference compound is said coordination compound, said coordination compound being potassium ferrocyanide.

10. A method of distinguishing a control solution from a sample during operation of an electrochemical sensor, the electrochemical sensor measuring the amount of an analyte, the method comprising the acts of:

providing a control solution including an internal reference compound, a buffer and a predetermined amount of analyte, said internal reference compound having a higher potential than the potential needed to measure the oxidation of said analyte, said internal reference compound being different from said buffer;

providing an electrochemical sensor having a working electrode and a counter electrode;

introducing said control solution to the electrochemical sensor;

applying a first potential to said electrochemical sensor, said lower first potential being sufficient to oxidize said analyte and not sufficient to oxidize said internal reference compound, and measuring the resulting electrical current;

after applying the first potential, applying a second potential to said electrochemical sensor sufficient to oxidize said internal reference compound and said analyte, and measuring the resulting electrical current;

calculating a Differential Index DI defined as DI=i high volt /i low volt

where:

i high volt is the current measured after applying the second potential, and i low volt is the current measured after applying the first potential;

if the Differential Index is sufficiently greater than 1, determining that a control solution is present; and

if the Differential Index is about 1, determining that a sample is present.

11. The method of claim 10 , wherein said analyte is glucose and said biological sample is whole blood.

12. The method of claim 10 , wherein said internal reference compound is an oxidizable organo-metallic compound, coordination compound, or organic amine compound.

13. The method of claim 12 , wherein said internal reference compound is said organic amine compound, said organic amine compound being 3-(N-morpholino) propane sulfonic acid, N-(2-hydroxyethyl)piperazine-N 1 -(2-ethane sulfonic acid), 2-[(2-Hydroxy-1,1-bis(hydroxy methyl)ethylamino]ethane sulfonic acid, 2-Morpholino ethane sulfonic acid, and Bis(2-hydroxyethyl)amino-tris (hydroxymethyl)methane[Bis-Tris], 4-aminobenzonitrile, 4-aminobenzoic acid, or 4-iodoaniline.

14. The method of claim 12 , wherein said internal reference compound is said oxidizable organo-metallic compound, said oxidizable organo-metallic compound being ferrocene or ferrocene derivatives.

15. The method of claim 12 , wherein said internal reference compound is said coordination compound, said coordination compound being potassium ferrocyanide.