Histamine Phosphate
(his' ta meen fos' fate).
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C5H9N3·2H3PO4 307.14

1H-Imidazole-4-ethanamine, phosphate (1:2).
Histamine phosphate (1:2) [51-74-1].
» 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.
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.
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Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 3412
Pharmacopeial Forum: Volume No. 29(5) Page 1504