Identification—
Add a volume of Injection, equivalent to about 50 mg of promethazine hydrochloride, to 20 mL of dilute hydrochloric acid (1 in 1000) contained in a separator. Wash the solution with a 20-mL portion of methylene chloride, discarding the washing. Add 2 mL of 1 N sodium hydroxide and 20 mL of methylene chloride, and shake for 2 minutes. Evaporate the methylene chloride extract on a steam bath with the aid of a stream of nitrogen to dryness. Dissolve the residue in 4 mL of carbon disulfide, filter through paper, if necessary, and determine the IR absorption spectrum as directed under
Identification—Organic Nitrogenous Bases 
181
, obtaining the spectrum of
USP Promethazine Hydrochloride RS as directed: the Injection meets the requirements of the test.
Assay—
Mobile phase—
Dissolve 1 g of sodium 1-pentanesulfonate in 500 mL of water, add 500 mL of acetonitrile and 5 mL of glacial acetic acid, filter, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Promethazine Hydrochloride RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with the same solvent to obtain a solution having a known concentration of about 0.1 mg per mL.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 50 mg of promethazine hydrochloride, to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 10.0 mL of the resulting solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.
System suitability preparation—
Dissolve a suitable quantity of phenothiazine in
Standard preparation to obtain a solution containing about 10 µg of phenothiazine per mL.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 30-cm column that contains packing L11. The flow rate is about 1.5 mL per minute. Chromatograph the
System suitability preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between the promethazine and phenothiazine peaks is not less than 3.0, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 30 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are 1.0 for promethazine and about 1.6 for phenothiazine. Calculate the quantity, in mg, of C
17H
20N
2S·HCl in each mL of the Injection taken by the formula:
500(C / V)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Promethazine Hydrochloride RS in the
Standard preparation,
V is the volume, in mL, of Injection taken, and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
