NOTE—Throughout the following procedures, protect test or assay specimens, the Reference Standard, and solutions containing them, by conducting the procedures without delay, under subdued light, or using low-actinic glassware.

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C17H20N2S·HCl dissolved by employing UV absorption at the wavelength of maximum absorbance at about 249 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of USP Promethazine Hydrochloride RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C17H20N2S·HCl is dissolved in 45 minutes.

Procedure for content uniformity— Transfer 1 finely powdered Tablet to a 100-mL volumetric flask, add 50 mL of citric acid solution (1 in 100), and shake by mechanical means for 15 minutes. Dilute with citric acid solution (1 in 100) to volume, and centrifuge about 50 mL of the mixture. Dilute an accurately measured portion of the clear solution, equivalent to 5 mg of promethazine hydrochloride, quantitatively with citric acid solution (1 in 100) to 100 mL. Concomitantly determine the absorbance of this solution and a Standard solution of USP Promethazine Hydrochloride RS in the same medium, having a known concentration of about 50 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 298 nm, with a suitable spectrophotometer, using citric acid solution (1 in 100) as the blank. Calculate the quantity, in mg, of C17H20N2S·HCl in the Tablet by the formula: in which T is the labeled quantity, in mg, of promethazine hydrochloride in the Tablet; D is the concentration, in µg per mL, of promethazine hydrochloride in the test solution based on the labeled quantity per Tablet and the extent of dilution; C is the concentration, in µg per mL, of USP Promethazine Hydrochloride RS in the Standard solution; and AU and AS are the absorbances of the solution from the Tablet and the Standard solution, respectively.

(Official January 1, 2007)

Buffered palladium chloride solution— Transfer 500 mg of palladium chloride to a 250-mL beaker, add 5 mL of hydrochloric acid, and warm on a steam bath. Add 200 mL of hot water in small quantities while stirring until solution is complete. Cool, dilute with water to 500 mL, and mix. Transfer 25 mL of this solution to a 500-mL volumetric flask. Add 50 mL of 1 N sodium acetate and 48 mL of 1 N hydrochloric acid, dilute with water to volume, and mix.

Standard preparation— Transfer about 31 mg of USP Promethazine Hydrochloride RS, accurately weighed, to a low-actinic 250-mL volumetric flask. Dissolve in 0.1 N hydrochloric acid, dilute with 0.1 N hydrochloric acid to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 6.25 mg of promethazine hydrochloride, to a low-actinic 125-mL separator. Add 20 mL of saturated potassium chloride solution, 10 mL of 1 N sodium hydroxide, and 10 mL of methanol, and extract the promethazine with three 20-mL portions of n-heptane. Filter the heptane extracts through anhydrous sodium sulfate and collect them in a low-actinic 125-mL separator. Extract the promethazine from the n-heptane solution with three 15-mL portions of 0.1 N hydrochloric acid, collect the acid extracts in a low-actinic 50-mL volumetric flask, dilute with 0.1 N hydrochloric acid to volume, and mix.

Procedure— Into separate test tubes, pipet 2-mL portions of the Standard preparation, the Assay preparation, and 0.1 N hydrochloric acid to provide a blank. Add 3.0 mL of Buffered palladium chloride solution to each tube, and mix. Concomitantly determine the absorbances of the solutions at the wavelength of maximum absorbance at about 470 nm, using a suitable spectrophotometer, and using the blank in the reference cell. Calculate the quantity, in mg, of promethazine hydrochloride (C17H20N2S·HCl) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Promethazine Hydrochloride RS in the Standard preparation; and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.