Method for accurately quantifying a chemical substance contained in a sample solution at a significantly low concentration of not more than 1×10−8M
View Patent ↗Provided is 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. A measurement system used for the method includes a counter electrode 13 , a first reference electrode 12 , a first working electrode 11 a , a second working electrode 11 b , a second reference electrode 14 and a gel-coated electrode 15 . The gel-coated electrode 15 is electrically equivalent to the second working electrode 11 b . The gel-coated electrode 15 comprises an electrode body 31 and a gel 34 . The surface of the electrode body 31 is coated with the gel 34 . The gel 34 contains a standard electrolyte and an ionic liquid. The gel 34 contains no water. The ionic liquid is hydrophobic and nonvolatile. The ionic liquid is composed of a cation and an anion. The standard electrolyte is composed of the cation and a halide ion.
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, a second reference electrode and a gel-coated electrode; wherein
the gel-coated electrode is electrically equivalent to the second working electrode;
the gel-coated electrode comprises an electrode body and a gel;
the surface of the electrode body is coated with the gel;
the gel contains a standard electrolyte and an ionic liquid;
the gel contains no water;
the ionic liquid is hydrophobic and nonvolatile;
the ionic liquid is composed of a cation and an anion; and
the standard electrolyte is composed of the cation selected from the following Group (I) and a halide ion selected from the group consisting of a chloride ion, a bromide ion and an iodide ion;
Group (I): cations represented by the following formulae IV-(1) to IV-(6):
where R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are the same as or different from each other, and each represents a hydrogen atom, a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group, and R 9 , R 10 ,R 11 , and R 12 are the same as or different from each other, and each represents a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group;
(b) bringing the counter electrode, the first reference electrode, the first working electrode, the second working electrode, the second reference electrode and the gel-coated 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 and the gel-coated 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. The method according to claim 1 , wherein,
the cation and the anion of the ionic liquid are selected from the following groups (I) and (II), respectively:
Group (I): cations represented by the following formulae IV-(1) to IV-(6):
where R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are the same as or different from each other, and each represents a hydrogen atom, a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group, and R 9 , R 10 , R 11 , and R 12 are the same as or different from each other, and each represents a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group;
Group (II): anions represented by the following formula V-(1) and V-(2):
where Rf 1 and Rf 2 are the same as or different from each other, and each represents a perfluoroalkyl group having carbon number of 1 to 4.
9. The method according to claim 1 , wherein,
the ionic liquid is selected from the following:
1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide,
1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1-ethyl-3-methylimidazolium triflate,
1-ethyl-3-methylimidazolium bis(pentafluoroethanesulfonyl)imide,
1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide,
1,3-diethylimidazolium triflate,
1-butyl-3-ethylimidazolium triflate,
1,2-dimethyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide,
1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1-butyl-3-methylimidazolium triflate,
1-isopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide,
N,N-propylmethylpyrrolidinium bis(trifluoromethanesulfonyl)imide,
propyltrimethyammonium bis(trifluoromethanesulfonyl)imide,
N,N-methylpropylpiperidinium bis(trifluoromethanesulfonyl)imide, or
N-butylpyridinium bis(trifluoromethanesulfonyl)imide.
10. 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, a second reference electrode and a gel-coated electrode; wherein
the gel-coated electrode is electrically equivalent to the second working electrode;
the gel-coated electrode comprises an electrode body and a gel;
the surface of the electrode body is coated with the gel;
the gel contains a standard electrolyte and an ionic liquid;
the gel contains no water;
the ionic liquid is hydrophobic and nonvolatile;
the ionic liquid is composed of a cation and an anion; and
the standard electrolyte is composed of the cation selected from the following Group (I) and a halide ion selected from the group consisting of a chloride ion, a bromide ion and an iodide ion;
Group (I): cations represented by the following formulae IV-(1) to IV-(6):
where R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are the same as or different from each other, and each represents a hydrogen atom, a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group, and R 9 , R 10 , R 11 , and R 12 are the same as or different from each other, and each represents a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group;
(b) bringing the counter electrode, the first reference electrode, the first working electrode, the second working electrode and the gel-coated 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 and the gel-coated 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.
11. The method according to claim 10 , 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.
12. The method according to claim 10 , wherein the first predetermined period t 1 is not less than 10 seconds and not more than 600 seconds.
13. The method according to claim 10 , wherein the second predetermined period t 2 is not less than 10 seconds and not more than 600 seconds.
14. The method according to claim 10 , wherein the oxidation-reduction substance is a ferrocene derivative.
15. The method according to claim 14 , wherein the ferrocene derivative is ferrocenecarboxylic acid.
16. The method according to claim 10 , wherein the chemical substance is an antibody.
17. The method according to claim 10 , wherein,
the cation and the anion of the ionic liquid are selected from the following groups (I) and (II), respectively:
Group (I): cations represented by the following formulae IV-(1) to IV-(6):
where R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are the same as or different from each other, and each represents a hydrogen atom, a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group, and R 9 , R 10 , R 11 , and R 12 are the same as or different from each other, and each represents a straight or branched alkyl group which may include a heteroatom, an aralkyl group, or an aryl group;
Group (II): anions represented by the following formulae V-(1) and V-(2);
where Rf 1 and Rf 2 are the same as or different from each other, and each represents a perfluoroalkyl group having carbon number of 1 to 4.
18. The method according to claim 10 , wherein,
the ionic liquid is selected from the following:
1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide,
1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1-ethyl-3-methylimidazolium triflate,
1-ethyl-3-methylimidazolium bis(pentafluoroethanesulfonyl)imide,
1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide,
1,3-diethylimidazolium triflate,
1-butyl-3-ethylimidazolium triflate,
1,2-dimethyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide,
1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1-butyl-3-methylimidazolium triflate,
1-isopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide,
1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide,
N,N-propylmethylpyrrolidinium bis(trifluoromethanesulfonyl)imide,
propyltrimethyammonium bis(trifluoromethanesulfonyl)imide,
N,N-methylpropylpiperidinium bis(trifluoromethanesulfonyl)imide, or
N-butylpyridinium bis(trifluoromethanesulfonyl)imide.