A: Prepare a solution of it in water containing 25 mg per mL (test solution). Separately apply 5 µL of the test solution and 5 µL of a Standard solution containing about 25 mg of USP Cephalexin RS per mL, prepared by dissolving it in water with the aid of 0.1 N hydrochloric acid to a suitable thin-layer chromatographic plate (see Chromatography 621) 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 UV light: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

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

C: A solution (1 in 100) responds to the tests for Chloride 191.

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

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

Procedure— Proceed as directed for Procedure in the test for Related compounds under 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 I is the concentration, in mg per mL, of each cephalexin-related substance other than cephalexin in the Test solution; W is the quantity, in mg, of Cephalexin Hydrochloride taken to prepare the Test solution; and a is 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 Assay under Cephalexin.

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

Procedure— Proceed as directed for Procedure in the Assay under 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.