A: The retention times of the 2major peaks in the chromatogram of the Assay preparationcorrespond to those in the chromatogram of the Standard preparationas obtained in the Assay.

B: Aportion of crushed Tablets,equivalent to about 10mg of methyldopa,responds to Identificationtest Cunder Methyldopa.

Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Times: 30minutes;60minutes.

PROCEDURE FOR METHYLDOPA —

Standard preparation— Dissolve an accurately weighed quantity of USP Methyldopa RSin Dissolution Medium,and dilute quantitatively with the same solvent to obtain a solution having a known concentration of about 275µg of anhydrous methyldopa per mL.

Ferrous tartrate solution— Dissolve 1g of ferrous sulfate,2g of potassium sodium tartrate,and 100mg of sodium bisulfite in water to make 100mL.Use a freshly prepared solution.

Buffer solution— Dissolve 50g of ammonium acetate in 1000mLof dilute alcohol (1in 5).Adjust with 6Nammonium hydroxide to a pHof 8.5.

Procedure— Filter 35mLof the solution under test through paper,and transfer an aliquot estimated to contain between 2mg and 3mg of methyldopa into a 100-mLvolumetric flask.Adjust the final volume,if necessary,with Dissolution Mediumto 10mL.To a second 100-mLvolumetric flask add 10.0mLof Standard preparation,and to a third 100-mLvolumetric flask add 10.0mLof Dissolution Mediumto provide a blank.Treat each flask as follows:Add by pipet 5mLof Ferrous tartrate solutionand,dilute with Buffer solutionto volume.Concomitantly determine the absorbances of the treated Standard preparationand test solution in 1-cm cells at the wavelength of maximum absorbance at about 520nm,with a suitable spectrophotometer,against the reagent blank.Calculate the amount of C10H13NO4dissolved,in mg,taken by the formula: in which Cis the concentration,in µg of anhydrous methyldopa per mL,of USP Methyldopa RSin the Standard preparation;Vis the volume,in mL,of the aliquot of test solution used;and AUand ASare the absorbances of the solutions from the test solution and the Standard preparation,respectively.

PROCEDURE FOR HYDROCHLOROTHIAZIDE —Determine the amount of C7H8ClN3O4S2dissolved from UVabsorbances at the wavelength of maximum absorbance at about 317nm in 1-cm cells,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 Hydrochlorothiazide RSin the same medium.

Tolerances— Not less than 80%(Q)of the labeled amount of methyldopa (C10H13NO4)is dissolved in 30minutes,and not less than 80%(Q)of the labeled amount of hydrochlorothiazide (C7H8ClN3O4S2)is dissolved in 60minutes.

Procedure for content uniformity— Proceed as directed in the Assay,except use the following Test preparationinstead of the Assay preparation.

Test preparation— Transfer 1Tablet to a 250-mLvolumetric flask,add 50mLof water,and shake gently,if necessary,to disintegrate the tablet.Do not sonicate.After the tablet has completely disintegrated,add 25mLof acetonitrile,and shake by mechanical means for 30minutes.Add 13mLof 1Nhydrochloric acid,and shake by mechanical means for an additional 5minutes.Dilute with water to volume,and mix.

pH2.8Sodium phosphate solution— Dissolve 11.04g of monobasic sodium phosphate in 950mLof water.Adjust this solution with phosphoric acid to a pHof 2.8.Transfer the solution to a 1-liter volumetric flask,add water to volume,and mix.Filter through a membrane filter.

Mobile phase— Prepare a solution containing 95volumes of pH2.8Sodium phosphate solutionand 5volumes of methanol.

Standard preparation— Transfer a suitable quantity of USP Methyldopa RSto a 100-mLvolumetric flask to obtain a solution having a known concentration of about 1mg of anhydrous methyldopa per mL.Add an accurately weighed quantity of USP Hydrochlorothiazide RSthat corresponds to the ratio of hydrochlorothiazide to methyldopa in the Tablets.Dissolve in 10mLof water,10mLof acetonitrile,and 5mLof 1Nhydrochloric acid.Dilute with water to volume,and mix.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 250mg of methyldopa,to a 250-mLvolumetric flask,and add 50mLof water,25mLof acetonitrile,and 13mLof 1Nhydrochloric acid.Shake the flask for 5minutes,dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 270-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate,about 2mLper minute,is adjusted until the relative retention times for methyldopa and hydrochlorothiazide are about 0.38and 1.0,respectively.Chromatograph five replicate injections of the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation is not more than 2.0%,and the resolution factor between methyldopa and hydrochlorothiazide is not less than 6.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph by means of a suitable microsyringe or sampling valve.Record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of methyldopa (C10H13NO4)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Methyldopa RSin the Standard preparation;and rUand rSare the responses of the methyldopa peak obtained from the Assay preparationand the Standard preparation,respectively.Calculate the quantity,in mg,of hydrochlorothiazide (C7H8ClN3O4S2)in the portion of Tablets taken by the same formula,reading “hydrochlorothiazide”instead of “methyldopa.”