Analysis method of 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient, treatment for amyotrophic lateral sclerosis, inhibition of progression of amyotrophic lateral sclerosis, and method of producing medicament containing 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient

A method of analyzing a phenylhydrazine content in a 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient, comprising:

• obtaining a first measured value by measuring a phenylhydrazine content in a phenylhydrazine standard solution including phenylhydrazine or a salt thereof, a first acidic water and a first water-soluble organic solvent and having a phenylhydrazine concentration in a range of 0.01 μg/mL to 10 μg/mL;
• obtaining a second measured value by measuring a phenylhydrazine content in a 3-methyl-1-phenyl-2-pyrazolin-5-one sample solution including a 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient, a second acidic water and a second water-soluble organic solvent;
• and
• detecting a phenylhydrazine content in a 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient based on the first measured value and the second measured value,
• wherein the first acidic water includes hydrochloric acid and has an acid concentration in a range of 0.01 mol/L to 1 mol/L, the first water-soluble organic solvent is at least one selected from the group consisting of acetonitrile and methanol and has a volume ratio of the first acidic water and the first water-soluble organic solvent in the phenylhydrazine standard solution in a range of 9:1 to 6:1 such that the phenylhydrazine or a salt thereof is soluble in the phenylhydrazine standard solution, the second acidic water includes hydrochloric acid and has an acid concentration in a range of 0.01 mol/L to 1 mol/L, and the second water-soluble organic solvent is at least one selected from the group consisting of acetonitrile and methanol and has a volume ratio of the second acidic water and the second water-soluble organic solvent in the 3-methyl-1-phenyl-2-pyrazoline-5-one sample solution in a range of 9:1 to 6:1 such that the 3-methyl-1-phenyl-2-pyrazolin-5-one active pharmaceutical ingredient is soluble in the 3-methyl-1-phenyl-2-pyrazolin-5-one sample solution.