A: Infrared Absorption 197K.

B: It responds to the tests for Sodium 191.

Solution A, Solution B, Mobile phase, Extraction solution, Dilution buffer, 10% Acetic acid solution, System suitability solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Cephapirin Benzathine.

Assay preparation— In duplicate, weigh about 50 mg of Cephapirin Sodium, and transfer into a 25-mL volumetric flask. Add about 2.5 mL of Extraction solution and 15.0 mL of Dilution buffer, and mix to dissolve. Add 7.0 mL of acetonitrile, and mix. Allow the flask to return to room temperature, and dilute with water to volume.

Procedure— Separately inject equal volumes (about 2 µL) of the duplicate Standard preparation and the duplicate Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in µg, of cephapirin (C17H17N3O6S2) in each mg of Cephapirin Sodium taken by the formula: in which P is the assigned potency, in µg of cephapirin per mg, of USP Cephapirin Sodium RS; WS and WU are the quantities of USP Cephapirin Sodium RS and Cephapirin Sodium, in mg, used to prepare the Standard preparation and the Assay preparation, respectively; VU and VS are the final volumes, in mL, of the Assay preparation and the Standard preparation, respectively; and rU and rS are the average peak areas of the cephapirin peaks obtained from the Assay preparation and the Standard preparation, respectively.