A: The retention times of the major peaks in the chromatogram of the Assay preparationcorrespond to those in the chromatogram of the Standard preparation,as obtained in the Assay.

B: Dissolve a portion of finely ground Tablets,equivalent to about 50mg of triamterene,in 25mLof methoxyethanol,mix,and filter.Use the filtrate as the Test solution.Prepare Standard solutions containing 1.5mg of USP Triamterene RSper mLof methoxyethanol (Standard solution 1)and containing 1mg of USP Hydrochlorothiazide RSper mLof methoxyethanol(Standard solution 2).Separately apply 2µLof the Test solutionand 2µLeach of Standard solution 1and Standard solution 2to a suitable thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Dry the spots with a current of air.Develop the plate in a solvent system consisting of a mixture of ethyl acetate,glacial acetic acid,and water (8:1:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,mark the solvent front,and allow to dry.Locate the spots under short-wavelength and long-wavelength UVlight:the intensity and the RFvalue of the principal spots obtained from the Test solutioncorrespond to those from Standard solution 1and Standard solution 2.

Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 75rpm.

Time: 30minutes.

Buffer solution,Mobile phase,and Chromatographic system— Proceed as directed in the Assay.

Procedure— Inject a volume (about 10µL)of a filtered portion of the solution under test into the chromatograph,record the chromatogram,and measure the responses for the major peaks.Calculate the amounts of triamterene (C12H11N7)and hydrochlorothiazide (C7H8ClN3O4S2)dissolved by comparison with a Standard solution having known concentrations of USP Triamterene RSand USP Hydrochlorothiazide RSin the same Mediumand similarly chromatographed.

Tolerances— Not less than 80%(Q)each of the labeled amounts of C12H11N7and C7H8ClN3O4S2is dissolved in 30minutes.

Solution A— Dissolve 0.68g of sodium acetate trihydrate in 100.0mLof water,adjust with glacial acetic acid to a pHof 5.0,and mix.

Solution B— Prepare a mixture of acetonitrile and methanol (75:25).

Mobile phase— Prepare a suitable filtered and degassed mixture of Solution Aand Solution B(90:10).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Prepare a solution of USP Benzothiadiazine Related Compound A RSin acetonitrile having a known concentration of 0.15mg per mL.Transfer 10.0mLof this solution to a 100-mLvolumetric flask,add 50mLof acetonitrile and 6mLof glacial acetic acid,dilute with water to volume,and mix.

Test solution— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 150mg of hydrochlorothiazide,to a 100-mLvolumetric flask.Add 60mLof acetonitrile and 6mLof glacial acetic acid,and sonicate for 10minutes.Cool,dilute with water to volume,mix,and filter.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 273-nm detector and a 3.9-mm ×30-cm column that contains 10-µm packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak areas due to benzothiadiazine related compound Ain the Standard solutionand the Test solution.The retention times,relative to benzothiadiazine related compound A,are about 1.5for hydrochlorothiazide and about 10for triamterene.Calculate the quantity,in mg,of benzothiadiazine related compound Ain the hydrochlorothiazide contained in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Benzothiadiazine Related Compound A RSin the Standard solution;and rUand rSare the peak areas of benzothiadiazine related compound Aobtained from the Test solutionand the Standard solution,respectively:not more than 1.0%is present.

Buffer solution— Transfer 6.9g of monobasic sodium phosphate and 1.43g of propylamine hydrochloride to a 1000-mLvolumetric flask,dissolve in about 900mLof water,adjust with 1Nsodium hydroxide to a pHof 5.5,dilute with water to volume,and mix.

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

Solvent mixture— Prepare a mixture of water,acetonitrile,and glacial acetic acid (85:10:5).

Standard preparation— Transfer about 25mg of USP Hydrochlorothiazide RS,accurately weighed,to a 100-mLvolumetric flask.Add 25Jmg of USP Triamterene RS,accurately weighed,Jbeing the ratio of the labeled amount,in mg,of triamterene to the labeled amount,in mg,of hydrochlorothiazide per Tablet.Add 10mLof acetonitrile,10mLof water,and 5mLof glacial acetic acid,sonicating for 2to 3minutes after each addition.Cool to room temperature,dilute with water to volume,and mix.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 50mg of hydrochlorothiazide,to a 200-mLvolumetric flask.Add about 100mLof Solvent mixture,place the volumetric flask in a sonic bath heated to between 45and 50,and sonicate for about 30minutes.Remove the flask from the bath,and carefully add 70mLof Solvent mixture.Allow to cool to room temperature,and dilute with Solvent mixtureto volume.Filter the solution,discarding the first few mLof the filtrate.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 4.0-mm ×25-cm column that contains packing L1.The flow rate is about 1.2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.65for hydrochlorothiazide and 1.0for triamterene;the resolution,R,between hydrochlorothiazide and triamterene 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 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Separately calculate the quantities,in mg,of triamterene (C12H11N7)and hydrochlorothiazide (C7H8ClN3O4S2)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of the relevant USP Reference Standard in the Standard preparation;and rUand rSare the peak responses of the relevant analyte obtained from the Assay preparationand the Standard preparation,respectively.