Colorimetric method and reagent used for the same

A reagent useful for a colorimetric method comprising:

• transferring an electron from an analyte to a coloring reagent that produces color by reduction via a mediator by using an oxidoreductase;
• and
• performing qualitative or quantitative analysis of the analyte by measuring color produced in the coloring reagent, and;
• the reagent comprising:
• an oxidoreductase;
• a mediator;
• and
• a coloring reagent for producing color by reduction,
• wherein the mediator is at least one selected from the group consisting of a copper complex, an iron complex, an osmium complex, and a ruthenium complex,
• wherein iron complex has a at least one ligand selected from the group consisting of ammonia, an imidazole compound, a phenanthroline compound, a triazine compound, a biquinoline compound, a pyridylazo compound, a nitroso compound, an oxine compound, a benzothiazole compound, and a derivative of each of the compounds, or the iron complex is selected from the group consisting of Fe(4,4′-dimethyl-2,2′-bipyridyl)3, Fe(4,4′-diphenyl-2,2′-bipyridyl)3, Fe(4,4′-diamino-2,2′-bipyridyl)3, Fe(4,4′-dihydroxy-2,2′-bipyridyl)3, Fe(4,4′-dicarboxy-2,2′-bipyridyl)3, Fe(4,4′-dibromo-2,2′-bipyridyl)3, Fe(5,5′-dimethyl-2,2′-bipyridyl)3, Fe(5,5′-diphenyl-2,2′-bipyridyl)3, Fe(5,5′-diamino-2,2′-bipyridyl)3, Fe(5 5′-dihydroxy-2,2′-bipyridyl)3, Fe(5,5′-dicarboxy-2,2′-bipyridyl)3, and Fe(5,5′-dibromo-2,2′-bipyridyl)3, and
• wherein the copper complex, the osmium complex, and the ruthenium complex have at least one ligand selected from the group consisting of ammonia, a bipyridyl compound, an imidazole compound, a phenanthroline compound, a triazine compound, a biquinoline compound, a pyridylazo compound, a nitroso compound, an oxine compound, a benzothiazole compound, and a derivative of each of the compounds.