A: Prepare a solution of it in water containing 25mg per mL(test solution).Separately apply 5µLof the test solution and 5µLof a Standard solution containing about 25mg of USP Cephalexin RSper mL,prepared by dissolving it in water with the aid of 0.1Nhydrochloric acid to a suitable thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,place the plate in a saturated chamber containing a solvent system consisting of a mixture of ethyl acetate,water,acetonitrile,and glacial acetic acid (42:18:14:14)and lined with filter paper.Develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,mark the solvent front,allow the plate to air-dry,and examine under short-wavelength UVlight:the RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

B: The UVabsorption spectrum of a solution (1in 50,000)exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Cephalexin RS,concomitantly measured.

C: Asolution (1in 100)responds to the tests for Chloride á191ñ.

Solution A ,Solution B,Mobile phase,Solvent,Standard solutions,and Chromatographic system—Proceed as directed for Related compoundsunder Cephalexin.

Test solution— Transfer about 30mg of Cephalexin Hydrochloride,accurately weighed,to a 5-mLvolumetric flask,dissolve in Solvent,dilute with Solventto volume,and mix.

Procedure— Proceed as directed for Procedurein the test for Related compoundsunder Cephalexin.Calculate the percentage of each cephalexin-related substance represented by each peak in the chromatogram obtained from the Test solution,other than the cephalexin peak,by the formula: in which Iis the concentration,in mg per mL,of each cephalexin-related substance other than cephalexin in the Test solution;Wis the quantity,in mg,of Cephalexin Hydrochloride taken to prepare the Test solution;and ais the content,in µg per mg,of cephalexin in the Cephalexin Hydrochloride taken,as determined in the Assay:not more than 1.0%of any individual cephalexin-related substance is found,and the sum of all cephalexin-related substances found is not greater than 5.0%.

Mobile phase ,Internal standard solution,Standard preparation,and Chromatographic system—Proceed as directed in the Assayunder Cephalexin.

Assay preparation— Transfer about 115mg of Cephalexin Hydrochloride,accurately weighed,to a 100-mLvolumetric flask,dissolve in water,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 50-mLglass-stoppered flask,add 15.0mLof Internal standard solution,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Cephalexin.Calculate the quantity,in µg,of cephalexin (C16H17N3O4S)in each mg of the Cephalexin Hydrochloride taken by the formula: in which the terms are as defined therein.