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

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

Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 30minutes.

Procedure— Determine the amount of C7H10N2OSdissolved from UVabsorbances at the wavelength of maximum absorbance at about 274nm 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 RSin the same medium.

Tolerances— Not less than 85%(Q)of the labeled amount of C7H10N2OSis dissolved in 30minutes.

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

Mobile phase— Prepare a filtered and degassed mixture of 0.025M Phosphate bufferand acetonitrile (80:20).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

Chromatographic system (see Chromatography á621ñ)—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 1mLper 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 3500theoretical 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 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak area responses for the major peaks.Calculate the quantity,in mg,of C7H10N2OSin the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Propylthiouracil RSin the Standard preparation,and rUand rSare the peak area responses of propylthiouracil obtained from the Assay preparationand the Standard preparation,respectively.