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

B: Transfer a quantity of finely ground Tablets,equivalent to about 100mg of diflunisal,to a 10-mLvolumetric flask,add 2mLof water,and sonicate for 5minutes.Dilute with methanol to volume,sonicate for an additional 5minutes,mix,and filter.Separately apply 10µLeach of the filtrate and a Standard solution of USP Diflunisal RSin methanol solution (4in 5)containing 10mg per mLto 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 n-hexane,glacial acetic acid,and chloroform (17:3:2)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 long-wavelength UVlight:the RFvalue of the principal spot in the chromatogram of the test solution corresponds to that obtained from the Standard solution.

pH7.20,0.1M Tris buffer— Dissolve 121g of tris(hydroxymethyl)aminomethane (THAM)in 9liters of water.Adjust the solution with a 7in 100solution of anhydrous citric acid in water to a pHof 7.45,at 25.Dilute with water to 10.0liters,equilibrate to 37,and adjust to a pHof 7.20,if necessary.

Medium: pH7.20,0.1M Tris buffer;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Procedure— Determine the amount of C13H8F2O3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 306nm of filtered portions of the solution under test,suitably diluted with pH7.20,0.1M Tris buffer,in comparison with a Standard solution having a known concentration of USP Diflunisal RSin the same Medium.

Tolerances— Not less than 80%(Q)of the labeled amount of C13H8F2O3is dissolved in 30minutes.

Procedure for content uniformity— Transfer 1finely powdered Tablet to a 200-mLvolumetric flask,add 50mLof water,shake by mechanical means for 30minutes,and sonicate for 2minutes.Add 100mLof alcohol to the flask,shake by mechanical means for 15minutes,and sonicate for 2minutes.Dilute with alcohol to volume,mix,and centrifuge a portion of the solution.Quantitatively dilute an accurately measured volume of the resultant clear supernatant with alcohol,if necessary,to obtain a test solution containing about 1.25mg per mL.Transfer about 125mg of USP Diflunisal RS,accurately weighed,to a 100-mLvolumetric flask,add 75mLof alcohol to dissolve,dilute with water to volume,and mix to obtain the Standard solution.Transfer 3.0mLeach of the Standard solution and the test solution to separate 50-mLvolumetric flasks.To each flask add 5.0mLof a solution containing 1g of ferric nitrate in 100mLof 0.08Nnitric acid,dilute with water to volume,and mix.Concomitantly determine the absorbances of the solutions at the wavelength of maximum absorbance at about 550nm,with a suitable spectrophotometer,using water as the blank.Calculate the quantity,in mg,of C13H8F2O3in the Tablet by the formula: in which Tis the labeled quantity,in mg,of diflunisal in the Tablet;Cis the concentration,in µg per mL,of USP Diflunisal RSin the Standard solution;Dis the concentration,in µg per mL,of diflunisal in the test solution,based upon the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solutions from the test solution and the Standard solution,respectively.

Standard preparation— Dissolve a suitable quantity of USP Diflunisal RSin a mixture of acetonitrile and water (60:40)to obtain a solution having a known concentration of about 1.0mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of diflunisal,to a 100-mLvolumetric flask containing about 5mLof water.Sonicate for 5minutes,add 60.0mLof acetonitrile,sonicate for an additional 5minutes,dilute with water to volume,mix,and filter.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 2.0mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure: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 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 diflunisal (C13H8F2O3)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Diflunisal RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.