Identification—
Dilute a volume of Injection with 0.1 N hydrochloric acid to obtain a solution having a concentration of about 20 µg of hydroxyzine hydrochloride per mL: the UV absorption spectrum of this solution exhibits maxima and minima at the same wavelengths as that of a 1 in 50,000 solution of
USP Hydroxyzine Hydrochloride RS in 0.1 N hydrochloric acid, concomitantly measured.
Assay and limit of 4-chlorobenzophenone—
Mobile phase—
Adjust about 1000 mL of
Buffer No. 1 (see
Phosphate Buffers and Other Solutions in the section
Media and Diluents, under
Antibiotics—Microbial Assays 
81
) with 10 N potassium hydroxide to a pH of 6.6. To about 35 volumes of this solution add about 65 volumes of methanol, mix, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve accurately weighed quantities of
USP Hydroxyzine Hydrochloride RS and 4-chlorobenzophenone in
Mobile phase, and dilute quantitatively with
Mobile phase to obtain a solution having known concentrations of about 250 µg of
USP Hydroxyzine Hydrochloride RS and 0.5 µg of 4-chlorobenzophenone per mL. Protect this solution from light.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 125 mg of hydroxyzine hydrochloride, to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pipet 10 mL of this solution into a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Protect this solution from light.
Chromatographic system
(see
Chromatography 621)—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 2 mL per 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 preparation is not more than 2.0%. The relative retention times are about 0.75 for 4-chlorobenzophenone and 1.0 for hydroxyzine.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of hydroxyzine hydrochloride (C
21H
27ClN
2O
2·HCl) in each mL of the Injection taken by the formula:
0.5(C / V)(rU / rS),
in which
C is the concentration, in µg per mL, of
USP Hydroxyzine Hydrochloride RS in the
Standard preparation;
V is the volume, in mL, of Injection taken; and
rU and
rS are the hydroxyzine peak responses obtained from the
Assay preparation and the
Standard preparation, respectively. The ratio of the response of the 4-chlorobenzophenone peak to that of the hydroxyzine peak obtained from the
Assay preparation does not exceed the corresponding ratio of peak responses obtained from the
Standard preparation (0.2%).
