Diphenhydramine Citrate
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 98.0percent and not more than 100.5percent of C17H21NO·C6H8O7,calculated on the dried basis.
Packaging and storage— Preserve in tight,light-resistant containers.
Identification—
A: Infrared Absorption á197Kñ.
Solution: 700µg per mL.
Medium: water.
C: It responds to the test for Citrate á191ñ.
Melting range á741ñ: between 146and 150,but the range between beginning and end of melting does not exceed 2.
Loss on drying á731ñ— Dry it at 105for 3hours:it loses not more than 0.5%of its weight.
Residue on ignition á281ñ— To about 8g,accurately weighed,add 5mLof sulfuric acid,and char.After the substance is thoroughly charred,add 4mLof nitric acid and a few drops of sulfuric acid,heat gently until fumes are no longer evolved,and ignite at 800±25until the carbon is consumed.Place in a muffle furnace at 550±50for about 1hour.Continue the ignition until constant weight is attained:not more than 0.1%remains.
Organic volatile impurities,Method Vá467ñ: meets the requirements.
Solvent— Use dimethyl sulfoxide.
Assay— Dissolve about 1.6g of Diphenhydramine Citrate,accurately weighed,in a mixture of 100mLof glacial acetic acid and 20mLof xylene.Add 20mLof mercuric acetate TS,and titrate with 0.1Nperchloric acid VS,determining the endpoint potentiometrically.Perform a blank determination,and make any necessary correction.Each mLof 0.1Nperchloric acid is equivalent to 44.75mg of C17H21NO·C6H8O7.
Auxiliary Information— Staff Liaison:Karen A Russo,Ph.D.,Scientist
Expert Committee:(PA1)Pharmaceutical Analysis 1
USP28–NF23Page 667
Phone Number:1-301-816-8379