A: It responds to Identificationtest Bunder Indomethacin for Injection.

B: Ignite a small amount of it on a platinum wire in a non-luminous flame:an intense yellow flame is produced.

C: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that of the Standard preparationas obtained in the Assay.

Standard solution— Transfer 1.0mLof acetone to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 1.0mLof this solution to a 200-mLvolumetric flask,dilute with water to volume,and mix.Insert the stopper,and cool in an ice bath.

Test solution— Transfer about 100mg of Indomethacin Sodium,accurately weighed,to a 15-mLcentrifuge tube,and dissolve in 1.0mLof cool water.While vortexing this solution,add 1.0mLof 0.24Nhydrochloric acid,centrifuge promptly,and filter the supernatant.Collect the filtrate in a suitable tube,cap,and cool in an ice bath.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 3-mm ×1.8-m column that contains support S3.The column temperature is maintained at 165.The carrier gas is nitrogen.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the capacity factor,k¢,for acetone is between 4and 7;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Using the solvent flush technique,with water as the flushing agent,separately inject equal volumes (about 3µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms for 6minutes,and measure the areas for the acetone peaks.Calculate the percentage of acetone in the portion of Indomethacin Sodium taken by the formula: in which 0.79is the specific gravity of acetone;WUis the quantity,in mg,of Indomethacin Sodium taken to prepare the Test solution;and rUand rSare the acetone peak areas obtained from the Test solutionand the Standard solution,respectively:not more than 0.1%is found.

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

Standard preparation— Transfer 2.0mLof the Stock impurity solution,prepared as directed in the Assay,to a 200-mLvolumetric flask,dilute with Diluentto volume,and mix.Each mLof this Standard preparationcontains 0.002mg of 4-chlorobenzoic acid and 0.002mg of 5-methoxy-2-methyl-3-indoleacetic acid.

Test preparation— Use the stock solution used to prepare the Assay preparationas directed in the Assay.

Procedure— [NOTE—Use peak areas where peaks responses are indicated.]Separately inject equal volumes (about 20µL)of the Standard preparationand the Test preparation,record the chromatograms for 25minutes,and measure the response for the peaks having retention times corresponding to the major peaks obtained in the chromatogram of the Standard preparation.The relative standard deviation for replicate injections of the Standard preparationis not more than 5.0%.Calculate the percentages of 4-chlorobenzoic acid and of 5-methoxy-2-methyl-3-indoleacetic acid in the portion of Indomethacin Sodium taken by the formula: in which rUand rSare the peak responses of the corresponding analytes obtained from the Test preparationand the Standard preparation,respectively,WUis the quantity,in mg,of Indomethacin Sodium taken to prepare the Assay preparation,as described in the Assay,and Lis the percentage of weight loss obtained in the test for Loss on drying:the sum of the percentages of 4-chlorobenzoic acid and 5-methoxy-2-methyl-3-indoleacetic acid does not exceed 0.2%.Calculate the percentage of each peak other than the solvent peak,the main indomethacin peak,the 4-chlorobenzoic acid peak,and the 5-methoxy-2-methyl-3-indoleacetic acid peak in the chromatogram of the Test preparationtaken by the formula: in which riis the response of each other peak and rtis the sum of the responses of all the peaks,excluding that of the solvent peak:not more than 0.5%of any individual peak is found,and the sum of these individual peaks is not more than 1.0%.

Mobile phase— Prepare a suitable filtered and degassed mixture of methanol,water,acetonitrile,and phosphoric acid (550:300:150:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluent— Prepare a sufficient quantity of a mixture of acetonitrile and water (3:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Indomethacin RSquantitatively in Diluentto obtain a stock solution containing 0.80mg per mL.Dilute an accurately measured volume of this stock solution quantitatively with Diluentto obtain a solution containing 0.16mg per mL(Standard preparation).

Assay preparation— Transfer about 100mg of Indomethacin Sodium,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Diluentto volume,and mix.Transfer 10.0mLof this stock solution to a 50-mLvolumetric flask,dilute with Diluentto volume,and mix.

Stock impurity solution— Dissolve accurately weighed quantities of 4-chlorobenzoic acid and 5-methoxy-2-methyl-3-indoleacetic acid quantitatively in Diluentto obtain a solution containing 0.20mg of each per mL.

Resolution solution— Prepare a mixture of the stock solution used to prepare the Diluent,the Standard preparation,and the Stock impurity solution(7:2:1).

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains packing L1,and is maintained at a temperature of 35±1.The flow rate is about 1.5mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed under Procedure:the capacity factor,k¢,for the indomethacin peak is not less than 2.5,the column efficiency determined from the indomethacin peak is not less than 3500theoretical plates,the tailing factor for the indomethacin peak is not more than 1.3,and the resolution,R,between the 4-chlorobenzoic acid peak and the 5-methoxy-2-methyl-3-indoleacetic acid peak is not less than 3.5.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]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.Calculate the quantity,in mg,of indomethacin sodium (C19H15ClNNaO4)in the portion of Indomethacin Sodium taken by the formula: in which 379.78and 357.79are the molecular weights of anhydrous indomethacin sodium and indomethacin,respectively,Cis the concentration,in mg per mL,of USP Indomethacin RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.