ANALYSIS METHOD OF 3-METHYL-1-PHENYL-2-PYRAZOLIN-5-ONE BULK DRUG, TREATMENT FOR AMYOTROPHIC LATERAL SCLEROSIS, INHIBITION OF PROGRESSION OF AMYOTROPHIC LATERAL SCLEROSIS, AND METHOD OF PRODUCING DRUG CONTAINING 3-METHYL-1-PHENYL-2-PYRAZOLIN-5-ONE BULK DRUG

This method of analyzing the phenylhydrazine content in a 3-methyl-1-phenyl-2-pyrazolin-5-one bulk drug involves: obtaining a first measured value by measuring the phenylhydrazine content of a standard solution that contains phenylhydrazine or a salt thereof, a first acidic water and a first water-soluble organic solvent, and that exhibits a phenylhydrazine concentration of 0.01 μg/mL to 10 μg/mL; obtaining a second measured value by measuring the phenylhydrazine content in a sample solution that contains a 3-methyl-1-phenyl-2-pyrazolin-5-one bulk drug, a second acidic water and a second water-soluble organic solvent; and detecting the phenylhydrazine content in the 3-methyl-1-phenyl-2-pyrazolin-5-one bulk drug on the basis of the first measured value and the second measured value. The first acidic water is at least one type selected from hydrochloric acid, an aqueous acetic acid solution, and the like, the first water-soluble organic solvent is at least one type selected from acetonitrile and methanol, the second acidic water is at least one type selected from hydrochloric acid, an aqueous acetic acid solution, and the like, and the second water-soluble organic solvent is at least one type selected from acetonitrile, and methanol.