Method for accurately quantifying a chemical substance contained in a sample solution at a significantly low concentration of not more than 1×10-

1. A method for accurately quantifying a chemical substance contained in a sample solution at a significantly low concentration of not more than 1×10 −8 M, the method comprising steps of:

(a) preparing a measurement system including a counter electrode, a first reference electrode, a first working electrode, a second working electrode and a second reference electrode;

(b) bringing the counter electrode, the first reference electrode, the first working electrode, the second working electrode and the second reference electrode into contact with the sample solution; wherein

the sample solution contains the chemical substance and an oxidation-reduction substance or contains the chemical substance modified with an oxidation-reduction substance;

(c) applying voltages of V 1 volts and V 2 volts (V 1 >V 2 ) to the first working electrode and the second working electrode, respectively, for a first predetermined period t 1 with use of a potentiostat so as to develop chemical reactions represented by the following chemical formulae (I) and (II) on the surfaces of the first working electrode and the second working electrode, respectively;

On the first working electrode:

(where, n represents an integer, and m represents a positive integer)

On the second working electrode:

(where, n represents an integer, and m represents a positive integer)

(d) stopping the application of the voltage to the second working electrode, when the first predetermined period t 1 elapses;

(e) leaving the sample solution as it stands for a second predetermined period t 2 after the step (d);

(f) measuring a voltage difference ΔE between the second working electrode and the second reference electrode after the step (e); and

(g) calculating a concentration of the chemical substance on the basis of the following formula (III)

Δ E=C 1·log 10 (the concentration of the chemical substance)+ C 2  (III)

C 1 : proportional constant

C 2 : constant.

2. The method according to claim 1 , wherein

the voltage difference between the voltages of V 1 and V 2 in the step (c) is not less than 0.3 volts and not more than 0.6 volts.

3. The method according to claim 1 , wherein

the first predetermined period t 1 is not less than 10 seconds and not more than 600 seconds.

4. The method according to claim 1 , wherein

the second predetermined period t 2 is not less than 10 seconds and not more than 600 seconds.

5. The method according to claim 1 , wherein

the oxidation-reduction substance is a ferrocene derivative.

6. The method according to claim 5 , wherein

the ferrocene derivative is ferrocenecarboxylic acid.

7. The method according to claim 1 , wherein

the chemical substance is an antibody.

8. A method for accurately quantifying a chemical substance contained in a sample solution at a significantly low concentration of not more than 1×10 −8 M, the method comprising steps of:

(a) preparing a measurement system including a counter electrode, a first reference electrode, a first working electrode, a second working electrode and a second reference electrode;

(b) bringing the counter electrode, the first reference electrode, the first working electrode and the second working electrode into contact with the sample solution; wherein

the sample solution contains the chemical substance and an oxidation-reduction substance or contains the chemical substance modified with an oxidation-reduction substance; and

the second reference electrode is not in contact with the sample solution;

(c) applying voltages of V 1 volts and V 2 volts (V 1 >V 2 ) to the first working electrode and the second working electrode, respectively, for a first predetermined period t 1 with use of a potentiostat so as to develop chemical reactions represented by the following chemical formulae (I) and (II) on the surfaces of the first working electrode and the second working electrode, respectively;

On the first working electrode:

(where, n represents an integer, and m represents a positive integer)

On the second working electrode:

(where, n represents an integer, and m represents a positive integer)

(d) stopping the application of the voltage to the second working electrode when the first predetermined period t 1 elapses;

(e) leaving the sample solution as it stands for a second predetermined period t 2 after the step (d);

(f) bringing the second reference electrode into contact with the sample solution;

(g) measuring a voltage difference ΔE between the second working electrode and the second reference electrode after the step (f); and

(h) calculating a concentration of the chemical substance on the basis of the following formula (III)

Δ E=C 1·log 10 (the concentration of the chemical substance)+ C 2  (III)

C 1 : proportional constant

C 2 : constant.

9. The method according to claim 8 , wherein

the voltage difference between the voltages of V 1 and V 2 in the step (c) is not less than 0.3 volts and not more than 0.6 volts.

10. The method according to claim 8 , wherein

the first predetermined period t 1 is not less than 10 seconds and not more than 600 seconds.

11. The method according to claim 8 , wherein

the second predetermined period t 2 is not less than 10 seconds and not more than 600 seconds.

12. The method according to claim 8 , wherein

the oxidation-reduction substance is a ferrocene derivative.

13. The method according to claim 12 , wherein

the ferrocene derivative is ferrocenecarboxylic acid.

14. The method according to claim 8 , wherein

the chemical substance is an antibody.