Method for quantitatively determining a reducing substance and a reagent for quantitative determination
The present invention provides a method for quantitatively determining a reducing substance, which comprises reacting a reducing substance in a test specimen with iron (III) ions, reacting iron (II) ions formed by reduction of the iron (III) ions or residual iron (III) ions with a metal indicator which is capable of reacting specifically with the iron (II) ions or the residual iron (III) ions to undergo color development, and carrying out quantitative determination by measuring the degree of color development, wherein a chelating agent which is specific to copper ions is added to the test specimen before the reaction of the reducing substance with the iron (III) ions; and a reagent used for it.
1. A method for quantitatively determining a reducing substance, which comprises, in order:
adding a chelating agent which is specific to copper ions, and at least one of an aluminum salt and a gallium salt, to a test specimen,
reacting a reducing substance in the test specimen with iron (III) ions thereby forming iron (II) ions,
reacting said iron (II) ions or residual iron (III) ions with a metal indicator which is capable of reacting specifically with the iron (II) ions or the residual iron (III) ions to undergo color development, and
carrying out quantitative determination by measuring the degree of color development.
2. The method for quantitatively determining a reducing substance according to claim 1 , wherein the chelating agent specific to the copper ions is at least one selected from the group consisting of neocuproine, bathocuproine and salts thereof.
3. The method for quantitatively determining a reducing substance according to claim 1 , further comprising adding an organic acid to the test specimen together with the at least one of an aluminum salt and a gallium salt.
4. The method for quantitatively determining a reducing substance according to claim 3 , wherein the organic acid is tartaric acid.
5. The method for quantitatively determining a reducing substance according to claim 1 , wherein the reducing substance is hydrogen sulfide or sulfide ions.
6. The method for quantitatively determining a reducing substance according to claim 5 , wherein the hydrogen sulfide or sulfide ions are formed by reacting a sulfur-containing amino acid contained in the test specimen with an enzyme which is capable of reacting with the sulfur-containing amino acid to form hydrogen sulfide.
7. The method for quantitatively determining a reducing substance according to claim 1 , wherein the iron (III) ions constitute a complex.
8. The method for quantitatively determining a reducing substance according to claim 7 , further comprising adding an auxiliary agent, which has an ability of coordinating ligands around the iron ions, to the test specimen together with the complex of the iron (III) ions.
9. The method for quantitatively determining a reducing substance according to claim 1 , wherein the test specimen is a biological specimen or an environmental specimen.
10. A reagent for quantitative determination of a reducing substance, which comprises a chelating agent which is specific to copper ions, at least one of an aluminum salt and a gallium salt, iron (III) ions, and a metal indicator which is capable of reacting specifically with iron (II) ions or iron (III) ions to undergo color development.
11. The reagent for quantitative determination of a reducing substance according to claim 10 , wherein the chelating agent which is specific to the copper ions is at least one selected from the group consisting of neocuproine, bathocuproine and salts thereof.
12. The reagent for quantitative determination of a reducing substance according to claim 10 , which further comprises an organic acid.
13. The reagent for quantitative determination of a reducing substance according to claim 12 , wherein the organic acid is tartaric acid.
14. The reagent for quantitative determination of a reducing substance according to claim 10 , which further comprises an enzyme which is capable of reacting with a sulfur-containing amino acid to form hydrogen sulfide.
15. The reagent for quantitative determination of a reducing substance according to claim 10 , wherein the iron (III) ions constitute a complex.
16. The reagent for quantitative determination of a reducing substance according to claim 15 , which further comprises an auxiliary agent which has an ability of coordinating ligands around the iron ions.
17. The reagent for quantitative determination of a reducing substance according to claim 10 , which comprises a first reagent comprising the copper chelating agent and the at least one of an aluminum salt and a gallium salt, and a second reagent comprising the iron (III) ions and the metal indicator.