A: Place a portion of Oral Solution, equivalent to 50 mg of diphenhydramine hydrochloride, in a separator, add 0.5 mL of 2 N sulfuric acid, and extract with three 15-mL portions of ether, discarding the extracts. Add 5 mL of water. In a second separator dissolve 50 mg of USP Diphenhydramine Hydrochloride RS in 25 mL of water. Treat each solution as follows. Add 2 mL of 1 N sodium hydroxide, and extract with 75 mL of n-heptane. Wash the n-heptane extract with 10 mL of water, evaporate the extract to dryness, and dissolve the residue in 4 mL of carbon disulfide. Pass through a dry filter to clarify the solution, if necessary, and proceed as directed under Identification—Organic Nitrogenous Bases 181, beginning with “Determine the absorption spectra of the filtered solutions”: the Oral Solution meets the requirements of the test.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

(Official January 1, 2007)

Mobile phase, Standard preparation, System suitability solution, and Chromatographic system— Prepare as directed in the Assay under Diphenhydramine Hydrochloride.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 50 mg of diphenhydramine hydrochloride, to a 100-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Diphenhydramine Hydrochloride. Calculate the quantity, in mg, of diphenhydramine hydrochloride (C17H21NO·HCl) in each mL of the Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Diphenhydramine Hydrochloride RS in the Standard preparation; V is the volume, in mL, of Oral Solution taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.