A: Boil a quantity of finely powdered Tablets, equivalent to about 100 mg of propylthiouracil, with 10 mL of alcohol under a reflux condenser for 20 minutes. Filter while hot, and evaporate the filtrate on a steam bath to dryness: a portion of the residue responds to the Identification tests under Propylthiouracil.

B: The chromatogram of the Assay preparation obtained as directed in the Assay exhibits a major peak, the retention time of which corresponds to that exhibited in the chromatogram of the Standard preparation.

Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C7H10N2OS dissolved from UV absorbances at the wavelength of maximum absorbance at about 274 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of USP Propylthiouracil RS in the same medium.

Tolerances— Not less than 85% (Q) of the labeled amount of C7H10N2OS is dissolved in 30 minutes.

(Official January 1, 2007)

0.025 M Phosphate buffer— Transfer an accurately weighed quantity of 3.40 g of monobasic potassium phosphate to a 1000-mL beaker. Add 500 mL of water, and stir until dissolved. Adjust the resulting solution with phosphoric acid or 0.1 N sodium hydroxide to a pH of 4.6. Add 500 mL of water to this solution, and mix.

Mobile phase— Prepare a filtered and degassed mixture of 0.025 M Phosphate buffer and acetonitrile (80:20). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer an accurately weighed quantity of about 25 mg of USP Propylthiouracil RS to a 50-mL volumetric flask, add 5 mL of methanol, and sonicate for 5 minutes. Add 25 mL of water, and shake by mechanical means for 15 minutes. Dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix to obtain a solution having a known concentration of about 50 µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder equivalent to about 50 mg of propylthiouracil to a 100-mL volumetric flask, add 10 mL of methanol, and sonicate for 5 minutes. Add 50 mL of water, and shake by mechanical means for 20 minutes. Dilute with water to volume, mix, and filter. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 272-nm detector and a 4.6-mm × 10-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as described for Procedure: the column efficiency, determined from the analyte peak, is not less than 3500 theoretical plates, the tailing factor, T, for the propylthiouracil peak is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

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 peak area responses for the major peaks. Calculate the quantity, in mg, of C7H10N2OS in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Propylthiouracil RS in the Standard preparation, and rU and rS are the peak area responses of propylthiouracil obtained from the Assay preparation and the Standard preparation, respectively.