For cephalexin —

Medium: water; 900 mL.

Apparatus 1— Use 40-mesh cloth and 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C16H17N3O4S dissolved from the UV absorbances at the wavelength of maximum absorbance at about 262 nm of a filtered portion of the solution under test, suitably diluted with Dissolution Medium, if necessary, to a concentration of about 20 µg per mL, in comparison with a Standard solution having a known concentration of USP Cephalexin RS in the same medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C16H17N3O4S is dissolved in 30 minutes.

For cephalexin hydrochloride —

Medium and Procedure—Proceed as directed under For cephalexin.

Apparatus 1— Use 10-mesh cloth and 150 rpm.

Time: 45 minutes.

Tolerances— Not less than 75% (Q) of the labeled amount of C16H17N3O4S is dissolved in 45 minutes.

Mobile phase , Internal standard solution, Standard preparation, and Chromatographic system—Prepare as directed in the Assay under Cephalexin.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed quantity of the powder, equivalent to about 500 mg of cephalexin, to a 500-mL volumetric flask, add water to volume, and mix. Sonicate, if necessary, to assure complete dissolution of the cephalexin. Filter, if necessary, to obtain a clear solution. Transfer 10.0 mL of this solution to a 50-mL, glass-stoppered flask, add 15.0 mL of Internal standard solution, mix, and filter.

Procedure— Proceed as directed for Procedure in the Assay under Cephalexin. Calculate the quantity, in mg, of C16H17N3O4S in the portion of Tablets taken by the formula: in which the terms are as defined therein.