Histamine Phosphate
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
C5H9N3 · 2H3PO4 307.14
1H-Imidazole-4-ethanamine, phosphate (1:2).
Histamine phosphate (1:2) CAS RN®: 51-74-1; UNII: QWB37T4WZZ.
Histamine Phosphate contains not less than 98.0 percent and not more than 101.0 percent of C5H9N3 · 2H3PO4, calculated on the dried basis.
Packaging and storage—Preserve in tight, light-resistant containers.
Identification—
A: Dissolve 0.10 g in a mixture of 7 mL of water and 3 mL of 1 N sodium hydroxide, and add the solution to a mixture of 50 mg of sulfanilic acid, 10 mL of water, 2 drops of hydrochloric acid, and 2 drops of sodium nitrite solution (1 in 10): a deep red color is produced. B: Dissolve 50 mg in 5 mL of hot water, add a hot solution of 50 mg of picrolonic acid in 10 mL of alcohol, and allow to crystallize. Filter the crystals with suction, wash with a small amount of ice-cold water, and dry at 105° for 1 hour: the crystals so obtained melt between 250° and 254°, with decomposition.
C: A solution (1 in 10) responds to the tests for Phosphate 〈191〉.
Loss on drying 〈731〉—Dry it at 105° for 2 hours: it loses not more than 3.0% of its weight.
Assay—Dissolve about 150 mg, accurately weighed, of Histamine Phosphate in 10 mL of water. Add 5 mL of chloroform and 25 mL of alcohol, then add 10 drops of thymolphthalein TS, and titrate with 0.2 N sodium hydroxide VS. Each mL of 0.2 N sodium hydroxide is equivalent to 15.36 mg of C5H9N3 · 2H3PO4.
