A: Crush a quantity of Tablets,equivalent to about 15mg of indapamide,remove and discard any coating material,and finely powder the remaining tablet cores.Agitate the powdered tablets with two 30-mLportions of 0.2Nsodium hydroxide in a centrifuge tube for 10minutes.Centrifuge each mixture,and combine the supernatants in a 250-mLseparator.Acidify the liquid with about 12mLof dilute hydrochloric acid (1in 10).Extract the acidic solution with two 4.0-mLportions of ether,filter the extracts through anhydrous sodium sulfate contained in a filter paper,and evaporate the ether,with the aid of a current of dry air,on a water bath.Dry the crystals at 105for 1hour:the crystals so obtained respond to Identificationtest Aunder Indapamide.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that of the Standard preparationobtained as directed in the Assay.

Medium: 0.05MpH6.8phosphate buffer (see Buffer Solutionsin the section Reagents,Indicators,and Solutions);900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

Mobile phase— Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Indapamide RSin methanol,and dilute quantitatively,and stepwise if necessary,with a mixture of Mediumand methanol (99:1)to obtain a solution having a known concentration equivalent to the solution under test.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 242-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 1.5mLper 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 50µL)of a filtered portion of the solution under test and the Standard solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Determine the amount of C16H16ClN3O3Sdissolved.

Tolerances— Not less than 75%(Q)of the labeled amount of C16H16ClN3O3Sis dissolved in 45minutes.

Mobile phase— Dissolve 1.08g of sodium 1-octanesulfonate in 700mLof water,add 10mLof glacial acetic acid,and mix.Add 300mLof acetonitrile,mix,filter,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of 2¢-chloroacetophenone in acetonitrile having a concentration of about 0.25mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Indapamide RSin acetonitrile to obtain a solution having a known concentration of about 0.1mg per mL.Transfer 5.0mLof this solution and 3.0mLof Internal standard solutionto a 50-mLvolumetric flask,dilute with a mixture of water and acetonitrile (50:10)to volume,and mix.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of powder,equivalent to about 2.5mg of indapamide,to a 50-mLvolumetric flask,add about 25mLof acetonitrile,and sonicate for about 20minutes.Cool,dilute with acetonitrile to volume,and mix.Transfer this solution to a 50-mLcentrifuge tube,and centrifuge at 2000rpm for about 10minutes.Transfer 10.0mLof the supernatant to a 50-mLvolumetric flask,add 3.0mLof Internal standard solution,dilute with a mixture of water and acetonitrile (70:4)to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 242-nm detector and a 4.5-mm ×10-cm column that contains a 3-µm 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 the analyte peak and the internal standard peak 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 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The retention time,relative to indapamide,is about 1.18for the internal standard.Calculate the quantity,in mg,of C16H16ClN3O3Sin the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Indapamide RSin the Standard preparation;and RUand RSare the ratios of the peak responses of indapamide to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.