Mobile phase— Adjust about 1000mLof Buffer No.1(see Phosphate Buffers and Other Solutionsin the section Media and Diluents,under Antibiotics—Microbial Assays á81ñ)with 10Npotassium hydroxide to a pHof 6.6.To about 35volumes of this solution add about 65volumes of methanol,mix,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve accurately weighed quantities of USP Hydroxyzine Hydrochloride RSand 4-chlorobenzophenone in Mobile phase,and dilute quantitatively with Mobile phaseto obtain a solution having known concentrations of about 250µg of USP Hydroxyzine Hydrochloride RSand 0.5µg of 4-chlorobenzophenone per mL.Protect this solution from light.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 125mg of hydroxyzine hydrochloride,to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Pipet 10mLof this solution into a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Protect this solution from light.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the tailing factors for the 4-chlorobenzophenone and hydroxyzine peaks are not more than 2.5,the resolution,R,between the 4-chlorobenzophenone and hydroxyzine peaks is not less than 2.0,and the relative standard deviation for replicate injections of the Standard preparationis not more than 2.0%.The relative retention times are about 0.75for 4-chlorobenzophenone and 1.0for hydroxyzine.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of hydroxyzine hydrochloride (C21H27ClN2O2·HCl)in each mLof the Injection taken by the formula: in which Cis the concentration,in µg per mL,of USP Hydroxyzine Hydrochloride RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and rUand rSare the hydroxyzine peak responses obtained from the Assay preparationand the Standard preparation,respectively.The ratio of the response of the 4-chlorobenzophenone peak to that of the hydroxyzine peak obtained from the Assay preparationdoes not exceed the corresponding ratio of peak responses obtained from the Standard preparation(0.2%).