A: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

B: Thin-Layer Chromatographic Identification Test á201ñ—

Mobile phase and Solvent mixture—Prepare as directed in the Assay.

Standard preparation— Dissolve a suitable quantity of 4-chlorobenzoic acid,accurately weighed,in acetonitrile to obtain a solution having a known concentration of about 0.22mg per mL.Transfer 1.0mLof this solution to a 500-mLvolumetric flask,add 150mLof acetonitrile,dilute with water to volume,and mix.This solution contains about 0.44µg of 4-chlorobenzoic acid per mL.

Test preparation— Use the Assay preparation.

Chromatographic system— Prepare as directed in the Assay.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,for the 4-chlorobenzoic acid peak is not less than 1.0.

Procedure— Separately inject equal volumes (about 50µL)of the Standard preparationand the Test preparationinto the chromatograph,record the chromatograms,and measure the 4-chlorobenzoic acid peak areas.Calculate the percentage of 4-chlorobenzoic acid in the portion of Indomethacin for Injection taken by the formula: in which C4is the concentration,in µg per mL,of 4-chlorobenzoic acid in the Standard preparation;Nis the number of containers of Indomethacin for Injection taken;CAis the quantity,in mg,of indomethacin (C19H16ClNO4)in each container of Indomethacin for Injection taken,determined as directed herein;and rUand rSare the 4-chlorobenzoic acid peak areas obtained from the Test preparationand the Standard preparation,respectively:not more than 2.2%,equivalent to not more than 5.0%,calculated as indomethacin,is found.

Mobile phase— Prepare a suitable mixture of methanol,water,and phosphoric acid (600:400:1),and pass through a suitable filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Solvent mixture— Prepare a mixture of water,acetonitrile,and phosphoric acid (700:300:1).

Standard preparation— Transfer about 20mg of USP Indomethacin RS,accurately weighed,to a 200-mLvolumetric flask,and dissolve in 60mLof acetonitrile.Dilute with water to volume,and mix.

Assay preparation— Select an accurately counted number of containers of Indomethacin for Injection,equivalent to a total of about 10mg of indomethacin,and constitute each with a volume of Solvent mixturesufficient to obtain solutions containing the equivalent of about 0.5mg of indomethacin per mL.Wash the contents of these containers with the aid of the Solvent mixtureinto a 100-mLvolumetric flask.Dilute with Solvent mixtureto volume,mix,and pass through a filter having a 0.5-µm or finer porosity.Use the filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 240-nm detector and a 3.9-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 for Procedure:the column efficiency determined from the indomethacin peak is not less than 1500theoretical plates;the capacity factor,k¢,for the indomethacin peak is not less than 3.5;the tailing factor for the indomethacin 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 50µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,CA,in mg,of indomethacin (C19H16ClNO4)in each container of Indomethacin for Injection taken by the formula: in which Cis the concentration,in mg per mL,of USP Indomethacin RSin the Standard preparation;Nis the number of containers of Indomethacin for Injection taken;and rUand rSare the indomethacin peak responses obtained from the Assay preparationand the Standard preparation,respectively.