Diphenhydramine Citrate
(dye'' fen hye' dra meen sit' rate).
C17H21NO·C6H8O7 447.48

Ethanamine, 2-(diphenylmethoxy)-N,N-dimethyl-, 2-hydroxy-1,2,3-propanetricarboxylate (1:1).
2-(Diphenylmethoxy)-N,N-dimethylethylamine citrate (1:1) [88637-37-0].
»Diphenhydramine Citrate contains not less than 98.0 percent and not more than 100.5 percent of C17H21NO·C6H8O7, calculated on the dried basis.
Packaging and storage— Preserve in tight, light-resistant containers.
USP Reference standards 11
USP Diphenhydramine Citrate RS Click to View Structure
Solution: 700 µg per mL.
Medium: water.
C: It responds to the test for Citrate 191.
Melting range 741: between 146 and 150, but the range between beginning and end of melting does not exceed 2.
Loss on drying 731 Dry it at 105 for 3 hours: it loses not more than 0.5% of its weight.
Residue on ignition 281 To about 8 g, accurately weighed, add 5 mL of sulfuric acid, and char. After the substance is thoroughly charred, add 4 mL of nitric acid and a few drops of sulfuric acid, heat gently until fumes are no longer evolved, and ignite at 800 ± 25 until the carbon is consumed. Place in a muffle furnace at 550 ± 50 for about 1 hour. Continue the ignition until constant weight is attained: not more than 0.1% remains.
Assay— Dissolve about 1.6 g of Diphenhydramine Citrate, accurately weighed, in a mixture of 100 mL of glacial acetic acid and 20 mL of xylene. Add 20 mL of mercuric acetate TS, and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 44.75 mg of C17H21NO·C6H8O7.
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Monograph Domenick Vicchio, Ph.D.
Senior Scientific Liaison
(SM42010) Monographs - Small Molecules 4
Reference Standards RS Technical Services
USP35–NF30 Page 2931