Mobile phase ,Phosphate buffer,Standard preparation,and Chromatographic system—Prepare as directed in the Assayunder Cefoxitin Sodium.

Assay preparation 1 (where it is represented as being in a single-dose container)—Constitute Cefoxitin 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 water to obtain a solution having a concentration of about 0.3mg of cefoxitin per mL.Use this solution within 5hours.

Assay preparation 2 (where the label states the quantity of cefoxitin in a given volume of constituted solution)—Constitute Cefoxitin 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 water to obtain a solution containing about 0.3mg of cefoxitin per mL.Use this solution within 5hours.

Procedure— Proceed as directed in the Assayunder Cefoxitin Sodium.Calculate the quantity,in mg,of cefoxitin (C16H17N3O7S2)in the portion of constituted solution taken by the formula: in which Lis the labeled quantity,in mg,in the portion of constituted solution taken,Dis the concentration,in mg per mL,of Assay preparation 1or Assay preparation 2,based on the volume of constituted solution taken and the extent of dilution,and the other terms are as defined therein.