A: Infrared Absorption á197Kñ,the potassium bromide-hydrochlorothiazide mixture previously being heated at 105for 2hours.

B: Ultraviolet Absorption á197Uñ

Diluent,Solution A,Solution B,Mobile phase,and System suitability solution— Proceed as directed in the Assay.

Quantitation limit solution— Dissolve an accurately weighed quantity of USP Hydrochlorothiazide RSinDiluent,sonicate if necessary,and dilute quantitatively,and stepwise if necessary,withDiluent to obtain a solution having a known concentration of about 0.16µg per mL.

Test solution— Proceed as directed for theAssay preparation in theAssay.

Chromatographic system(see Chromatography á621ñ)— Prepare as directed in theAssay.Chromatograph theSystem suitability solution,and record the peak responses as directed forProcedure:the resolution,R,between benzothiadiazine related compound Aand chlorothiazide is not less than 2.0and the resolution,R,between chlorothiazide and hydrochlorothiazide is not less than 1.5;the tailing factor for the benzothiadiazine related compound A,chlorothiazide,and hydrochlorothiazide peaks is not more than 1.5;and the relative standard deviation for replicate injections determined from benzothiadiazine related compound Aand chlorothiazide is not more than 5.0%.Chromatograph three replicate injections of theQuantitation limit solution,and record the peak responses as directed forProcedure:the relative standard deviation is not more than 25%.[NOTE—The relative retention times for benzothiadiazine related compound A,chlorothiazide,hydrochlorothiazide,5-chlorohydrochlorothiazide,and hydrochlorothiazide dimer [6-chloro-N-[(6-chloro-7-sulfamoyl-2,3-dihydro-4H-1,2,4-benzothiadiazine-4-yl 1,1-dioxide)methyl]3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide]are about 0.5,0.8,1.0,2.1,and 2.6,respectively.]

Procedure— Inject a volume (about 10µL)of theTest solution into the chromatograph,record the chromatogram,and measure the peak responses.Calculate the percentage of each impurity in the portion of Hydrochlorothiazide taken by the formula: in whichricis the ratio of the peak area for each impurity to its response factor;andrscis the sum of ratios of all the peak areas to their respective response factors,the response factors being 0.54,0.63,and 1.0for benzothiadiazine related compound A,chlorothiazide,and all other peaks,respectively:not more than 1.0%of benzothiadiazine related compound Ais found;not more than 0.5%of any other impurity is found;and not more than 0.9%of total other impurities excluding benzothiadiazine related compound Ais found.

Solvent— Use dimethyl sulfoxide.

Sodium phosphate solution— Transfer 2.76g of monobasic sodium phosphate,accurately weighed,into a 1000-mLvolumetric flask,and add about 990mLof water.Adjust with phosphoric acid to a pHof 2.7±0.1,and dilute with water to volume.Make adjustments if necessary (seeSystem SuitabilityunderChromatography á621ñ).

Diluent— Prepare a mixture ofSodium phosphate solution and acetonitrile (7:3).

Solution A— Prepare and degas a mixture of acetonitrile and methanol (3:1).

Solution B— Prepare and degas a solution of anhydrous formic acid in water (5in 1000).

Mobile phase— Use variable mixtures ofSolution AandSolution Bas directed forChromatographic system.Make adjustments if necessary (seeSystem Suitability underChromatography á621ñ).

System suitability solution— Dissolve suitable quantities of USP Hydrochlorothiazide RS,USP Chlorothiazide RS,and USP Benzothiadiazine Related Compound A RSinDiluent,sonicate if necessary,and dilute withDiluent to obtain a solution containing about 0.32mg per mL,0.0032mg per mL,and 0.0032mg per mL,respectively.Pass a portion through a filter having a 0.45-µm or finer porosity.

Standard preparation— Dissolve an accurately weighed quantity of USP Hydrochlorothiazide RSinDiluent,sonicate if necessary,and dilute quantitatively,and stepwise if necessary,withDiluent to obtain a solution having a known concentration of about 0.32mg per mL.Pass a portion through a filter having a 0.45-µm or finer porosity before injection.

Assay preparation— Transfer about 32mg of Hydrochlorothiazide,accurately weighed,to a 100-mLvolumetric flask.Add about 70mLofDiluent,sonicate for 10minutes if necessary to dissolve,and allow to cool to ambient temperature.Dilute withDiluent to volume,mix,and pass a portion through a filter having a 0.45-µm or finer porosity before injection.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 275-nm detector and 4.6-mm ×5-cm column that contains 3.5-µm packing L1.The flow rate is about 1.0mLper minute.The column temperature is maintained at 35.The chromatograph is programmed as follows. Chromatograph theDiluent to check for interference by system related peaks.Chromatograph theSystem suitability solution,and record the peak responses as directed forProcedure:the relative retention times are about 0.5for benzothiadiazine related compound A,0.8for chlorothiazide,and 1.0for hydrochlorothiazide;the resolution,R,between benzothiadiazine related compound Aand chlorothiazide is not less than 2.0and the resolution,R,between chlorothiazide and hydrochlorothiazide is not less than 1.5;and the tailing factor for the benzothiadiazine related compound A,chlorothiazide,and hydrochlorothiazide peaks is not more than 1.5.Chromatograph theStandard preparation,and record the peak responses as directed forProcedure:the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)of theStandard preparation and theAssay preparation into the chromatograph,record the chromatograms,and measure the responses for the hydrochlorothiazide peaks.Calculate the quantity,in mg,of C7H8ClN3O4S2in the portion of Hydrochlorothiazide taken by the formula: in whichCis the concentration,in mg per mL,of USP Hydrochlorothiazide RSin theStandard preparation;andrUandrSare the peak responses obtained from theAssay preparation and theStandard preparation,respectively.