Standard preparation— Prepare a solution,containing about 125µg of USP Indomethacin RSper mL,by first dissolving the Reference Standard in a volume of methanol that is one one-hundredth of the volume of the solution to be prepared,then adding ether to volume,and mixing.

Test preparation— Use the ether extract contained in the 200-mLvolumetric flask obtained as directed under Assay preparationin the Assay.

Procedure— Separately apply 10µLeach of the Test preparationand the Standard preparationto a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Develop the chromatogram in a solvent system consisting of a mixture of chloroform and glacial acetic acid (19:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the chamber,air-dry,and examine under short-wavelength UVlight:the RFvalue of the principal spot in the chromatogram of the Test preparationcorresponds to that obtained from the Standard preparation.

Medium: 0.1M,pH7.2phosphate buffer (see Buffer Solutionsin the section Reagents,Indicators,and Solutions);900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Procedure— Determine the amount of C19H16ClNO4dissolved from UVabsorbances at the wavelength of maximum absorbance at about 320nm of filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Indomethacin RSin the same medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C19H16ClNO4is dissolved in 60minutes.

Procedure for content uniformity— Place 1Suppository into a 100-mLvolumetric flask containing 80mLof a solution of methanol and glacial acetic acid (199:1),shake by mechanical means until the Suppository is dissolved,dilute with the methanol-glacial acetic acid solution to volume,and mix.Filter a portion of the solution,discarding the first 15mLof the filtrate,and dilute an accurately measured volume of the clear filtrate quantitatively and stepwise,if necessary,with the methanol–glacial acetic acid solution to obtain a solution containing about 25µg of indomethacin per mL.Concomitantly determine the absorbances of this solution and of a Standard solution of USP Indomethacin RSin the same medium having a known concentration of about 25µg per mLat the wavelength of maximum absorbance at about 320nm,with a suitable spectrophotometer,using the methanol–glacial acetic acid solution as the blank.Calculate the quantity,in mg,of C19H16ClNO4in the Suppository taken by the formula: in which Tis the labeled quantity,in mg,of indomethacin in the Suppository,Cis the concentration,in µg per mL,of USP Indomethacin RSin the Standard solution,Dis the concentration,in µg per mL,of indomethacin in the solution from the Suppository,on the basis of the labeled quantity per Suppository and the extent of dilution,and AUand ASare the absorbances of the solution from the Suppository and the Standard solution,respectively.

Solvent mixture— Prepare a solution of methanol and glacial acetic acid (199:1).

Standard preparation— Prepare a solution,having a known concentration of about 165µg of USP Indomethacin RSper mL,by first dissolving an accurately weighed quantity of the Reference Standard in a volume of methanol that is one one-hundredth of the nominal volume of the volumetric flask being used,then adding ether to volume,and mixing.Transfer 15.0mLof the resulting solution to a 100-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix to obtain a Standard preparationhaving a known concentration of about 25µg of USP Indomethacin RSper mL.

Assay preparation— Weigh,mash,and then mix not less than 10Suppositories.Transfer an accurately weighed portion of the mass,equivalent to about 25mg of indomethacin,to a 125-mLseparator,add 15mLof water and 50mLof ether,and shake until the mass is dissolved.Transfer the ether layer to a 200-mLvolumetric flask,extract the aqueous layer with two additional 50-mLportions of ether,and combine the ether extracts in the 200-mLvolumetric flask.Discard the aqueous layer.Dilute with Solvent mixtureto volume,and mix.Pipet 10mLof this solution into a 50-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.

Procedure— Concomitantly determine the absorbances of the Assay preparationand the Standard preparationat the wavelength of maximum absorbance at about 320nm,with a suitable spectrophotometer,using Solvent mixtureas a blank.Calculate the quantity,in mg,of C19H16ClNO4in the portion of Suppositories taken by the formula: in which Cis the concentration,in µg per mL,of USP Indomethacin RSin the Standard preparation,and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.