Mobile phase, Standard preparation, Resolution solution, and Chromatographic system— Proceed as directed in the Assay under Cephradine.

Assay preparation 1 (where it is represented as being in a single-dose container)—Constitute Cephradine for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Withdraw all of the withdrawable contents, using a suitable hypodermic needle and syringe, and dilute quantitatively with Mobile phase to obtain a solution containing about 0.5 mg of cephradine per mL.

Assay preparation 2 (where the label states the quantity of cephradine in a given volume of constituted solution)—Constitute Cephradine for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Dilute an accurately measured volume of the constituted solution quantitatively with Mobile phase to obtain a solution containing about 0.5 mg of cephradine per mL.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and Assay preparation 1 or Assay preparation 2 into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of cephradine (sum of cephradine and cephalexin) withdrawn from the container, or in the portion of constituted solution taken by the formula: in which C is the concentration, in mg per mL, of USP Cephradine RS in the Standard preparation; P is the designated potency, in µg per mg, of USP Cephradine RS; L is the labeled quantity, in mg of cephradine, in the container taken to prepare Assay preparation 1, or in the volume of constituted solution taken to prepare Assay preparation 2; D is the concentration, in mg of cephradine per mL, of Assay preparation 1 or Assay preparation 2, based on the labeled quantity in the container or in the portion of constituted solution taken, respectively, and the extent of dilution; and rU and rS are the sums of the cephradine and cephalexin peak responses obtained from Assay preparation 1 or Assay preparation 2 and the Standard preparation, respectively.