A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Standard preparations— Dissolve USP Indapamide RSin methanol,and mix to obtain Standard preparation Ahaving a known concentration of 0.30mg per mL.Dilute quantitatively with methanol to obtain Standard preparation Band Standard preparation Ccontaining 0.15mg and 0.075mg of USP Indapamide RSper mL,respectively.

Test preparation— Dissolve an accurately weighed quantity of Indapamide in methanol,and dilute quantitatively with methanol to obtain a solution containing 30mg per mL.

Procedure— Apply separately 10µLof the Test preparationand 10µLof each Standard preparationto a suitable thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Position the plate in a chromatographic chamber,and develop the chromatograms in a solvent system consisting of a mixture of toluene,ethyl acetate,and glacial acetic acid (70:30:1)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 dry under a current of air.Examine the plate under short-wavelength UVlight,and compare the intensities of any secondary spots observed in the chromatogram of the Test preparationwith those of the principal spots in the chromatograms of the Standard preparations:no secondary spot from the chromatograms of the Test preparationis larger or more intense than the principal spot obtained from Standard preparation B(0.5%),and the sum of the intensities of the secondary spots obtained from the Test preparationcorresponds to not more than 2.0%.

Mobile phase— Prepare a filtered and degassed mixture consisting of water,acetonitrile,methanol,and glacial acetic acid (650:175:175:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Dissolve a suitable quantity of p-chloroacetanilide in methanol to obtain a solution having a concentration of about 5.0mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Indapamide RSin Internal standard solution,and dilute quantitatively with Mobile phaseto obtain a solution having a known concentration of about 1.0mg per mLof the Reference Standard and about 0.25mg per mLof the internal standard.

Assay preparation— Transfer about 100mg of Indapamide,accurately weighed,to a 100-mLvolumetric flask,dissolve in 5.0mLof Internal standard solution,dilute with Mobile phaseto 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 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the resolution,R,between any peak of interest and any adjacent peak is not less than 2.0,the tailing factor for the analyte peak is not more than 2.0,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 5µL)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 0.65for p-chloroacetanilide.Calculate the quantity,in mg,of C16H16ClN3O3Sin the portion of Indapamide 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 area of indapamide to the peak area of internal standard in the Assay preparationand the Standard preparation,respectively.