A: To a portion of powdered Tablets,equivalent to about 300mg of metronidazole,add 20mLof dilute hydrochloric acid (1in 100),shake for several minutes,and filter:suitable aliquots of the filtrate respond to Identificationtest Bunder Metronidazole.

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

Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 1: 100rpm.

Time: 60minutes.

Procedure— Determine the amount of C6H9N3O3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 278nm of filtered portions of the solution under test,suitably diluted with 0.1Nhydrochloric acid,in comparison with a Standard solution having a known concentration of USP Metronidazole RSin the same medium.

Tolerances— Not less than 85%(Q)of the labeled amount of C6H9N3O3is dissolved in 60minutes.

Procedure for content uniformity— Transfer one Tablet to a 250-mLvolumetric flask,add about 100mLof dilute hydrochloric acid (1in 100),and shake for 30minutes.Dilute with dilute hydrochloric acid (1in 100)to volume,and mix.Filter,discarding the first 15mLof the filtrate.Dilute the filtrate quantitatively with dilute hydrochloric acid (1in 100),to obtain a solution having a concentration of about 0.2mg of metronidazole per mL.Pipet 10mLof this solution into a 100-mLvolumetric flask,dilute with dilute hydrochloric acid (1in 100)to volume,and mix.Concomitantly determine the absorbance of this test solution and that of a similarly prepared Standard solution of USP Metronidazole RS,having a known concentration of about 20µg per mL,in 1-cm matched cells,at the wavelength of maximum absorbance at about 278nm,with a suitable spectrophotometer,using dilute hydrochloric acid (1in 100)as the blank.Calculate the quantity,in mg,of C6H9N3O3in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of the metronidazole in the Tablet;Cis the concentration,in µg per mL,of USP Metronidazole RSin the Standard solution;Dis the concentration,in µg per mL,of metronidazole in the test solution,on the basis of the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the test solution and the Standard solution,respectively.

Mobile phase— Prepare a filtered and degassed mixture of water and methanol (80:20),making adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Metronidazole RSin Mobile phaseto obtain a solution having a known concentration of about 0.5mg per mL.

Assay preparation— Transfer to a suitable size volumetric flask 10Tablets,whole or ground,which when diluted with methanol will yield a solution having a concentration of about 10mg per mL.Add methanol,and shake by mechanical means for 30minutes or until the Tablets are disintegrated.Dilute with methanol to volume,and allow the solution to stand until the insoluble material has settled.Pipet 5.0mLof the clear supernatant into a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Filter the solution.

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 L7.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak response as directed under Procedure:the tailing factor is not more than 2,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of metronidazole (C6H9N3O3)in the portion of Tablets taken by the formula: in which Lis the labeled amount,in mg,of Metronidazole in each Tablet;Dis the concentration,in mg per mL,of Metronidazole in the Assay preparationbased on the labeled quantity per Tablet and the extent of dilution;Cis the concentration,in mg per mL,of USP Metronidazole RSin the Standard preparation;and rUand rSare the metronidazole peak responses obtained from the Assay preparationand the Standard preparation,respectively.