Medium: 0.1Nhydrochloric acid containing 0.1%sodium lauryl sulfate;900mL.

Apparatus 2: 75rpm.

Time: 60minutes.

Standard solution— Prepare a solution of USP Spironolactone RSand USP Hydrochlorothiazide RSin a mixture of methanol and Dissolution Medium(1:1)having accurately known concentrations of about 0.0125mg of each per mL.

Test solution— Transfer a 5.0-mLportion of the solution under test to a 10-mLvolumetric flask,dilute with methanol to volume,and mix.

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

Tolerances— Not less than 75%(Q)of each of the labeled amounts of C24H32O4Sand C7H8ClN3O4S2is dissolved in 60minutes.

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (7:3).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve accurately weighed quantities of USP Spironolactone RSand USP Hydrochlorothiazide RSin methanol to obtain a solution having known concentrations of about 50µg of each per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 25mg of spironolactone,to a 100-mLvolumetric flask,add about 70mLof methanol,shake by mechanical means for 30minutes,dilute with methanol to volume,mix,and centrifuge.Transfer 20.0mLof the resultant clear liquid to a 100-mLvolumetric flask,dilute with methanol to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between hydrochlorothiazide and spironolactone is not less than 2.0;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.The relative retention times are about 0.5for hydrochlorothiazide and 1.0for spironolactone.Calculate the quantity,in mg,of spironolactone (C24H32O4S)in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Spironolactone RSin the Standard preparation;and rUand rSare the responses of the spironolactone peak obtained from the Assay preparationand the Standard preparation,respectively.Calculate the quantity,in mg,of hydrochlorothiazide (C7H8ClN3O4S2)by the same formula,changing the terms to refer to hydrochlorothiazide.