Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Mobile phase— Prepare a suitable degassed solution of methanol and 0.05Mmonobasic sodium phosphate (6:4).

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 232-nm detector and a 4.6-mm ×25-cm column that contains packing L9.The flow rate is about 1.9mLper minute.Chromatograph replicate injections of a Standard solution,and record the peak responses as directed under Procedure:the relative standard deviation is not more than 2.0%.

Procedure— Inject alternately 50µLof a filtered portion of the solution under test and a Standard solution,having a known concentration of USP Hydroxyzine Hydrochloride RSin the same medium,into the chromatograph,record the chromatogram,and measure the response for the major peak.Determine the amount of C21H27ClN2O2·2HCl dissolved from the peak response obtained in comparison with the peak response obtained from the Standard solution.

Tolerances— Not less than 75%(Q)of the labeled amount of C21H27ClN2O2·2HCl is dissolved in 60minutes.

Mobile phase— Dissolve 7.0g of monobasic sodium phosphate in 1000mLof water,and adjust with phosphoric acid to a pHof 4.4.Pass the solution through a 5-µm porosity polytef membrane filter.Mix 900mLof the filtrate with 900mLof methanol,and degas by stirring under vacuum prior to use.

Standard preparation— Dissolve an accurately weighed quantity of USP Hydroxyzine Pamoate RSin methanol to obtain a solution having a known concentration of about 0.18mg per mL(equivalent to about 0.1mg of hydroxyzine hydrochloride per mL).

Assay preparation— Transfer,as completely as possible,the contents of not less than 20Capsules to a tared beaker,and determine the average weight per capsule.Mix the combined contents,and transfer an accurately weighed portion,equivalent to about 25mg of hydroxyzine hydrochloride,to a 250-mLvolumetric flask.Add 200mLof methanol to the flask,sonicate for 5minutes,shake by mechanical means for 30minutes,and sonicate for 2minutes.Dilute with methanol to volume,and mix.Filter the solution through a 5-µm porosity polytef membrane filter equipped with a glass fiber prefilter.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 232-nm detector and a 4.6-mm ×25-cm column that contains packing L9.The flow rate is about 2.5mLper minute.Chromatograph four replicate injections of the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto the chromatograph by means of a suitable microsyringe or sampling valve,record the chromatograms,and measure the responses for the major peaks.The retention time is about 6minutes for hydroxyzine.Calculate the equivalent quantity,in mg,of hydroxyzine hydrochloride (C21H27ClN2O2·2HCl)in the portion of Capsules taken by the formula: in which 447.83and 763.27are the molecular weights of hydroxyzine hydrochloride and hydroxyzine pamoate,respectively;Cis the concentration,in mg per mL,of USP Hydroxyzine Pamoate RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.