pH 7.4 Buffer, Mobile phase, and Chromatographic system— Prepare as directed in the Assay under Warfarin Sodium.

Standard preparation— Transfer about 94 mg of USP Warfarin RS, accurately weighed, to a 100-mL volumetric flask, and dissolve in 39.1 mL of 0.1 N sodium hydroxide. Add 25.0 mL of 0.2 M monobasic potassium phosphate, dilute with water to volume, and mix. Pipet 5 mL of this solution into a 50-mL volumetric flask, dilute with pH 7.4 Buffer to volume, and mix.

Assay preparation— Dissolve the contents of not fewer than 10 containers of Warfarin Sodium for Injection in a sufficient volume, accurately measured, of pH 7.4 Buffer to obtain a solution containing about 1 mg of warfarin sodium per mL. Pipet 5 mL of the resulting solution into a 50-mL volumetric flask, dilute with pH 7.4 Buffer to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Warfarin Sodium. Calculate the average quantity, in mg, of warfarin sodium (C19H15NaO4) in each container of Warfarin Sodium for Injection taken by the formula: in which 330.31 and 308.34 are the molecular weights of warfarin sodium and warfarin, respectively; V is the volume, in mL, of the solution prepared from the contents of the 10 or more containers; C is the concentration, in mg per mL, of USP Warfarin RS in the Standard preparation; N is the number of containers taken; and rU and rS are the peak responses of warfarin obtained from the Assay preparation and the Standard preparation, respectively.