A: The chromatogram of the Assay preparationobtained as directed in the Assayexhibits a major peak for cefoxitin,the retention time of which corresponds to that exhibited in the chromatogram of the Standard preparationobtained as directed in the Assay.

B: Ultraviolet Absorption á197Uñ—

Solution: 20µg per mL.

Medium: phosphate buffer (prepared by dissolving 1.0g monobasic potassium phosphate and 1.8g of anhydrous dibasic sodium phosphate in water to make 1000mL).

C: Asolution (1in 20)responds to the tests for Sodium á191ñ.

Test solution: 10mg per mL,in methanol.

Standard preparation— Transfer 5.0mLof acetone to a 1000-mLvolumetric flask,dilute with water to volume,and mix (Solution A).Transfer 5.0mLof methanol to a 1000-mLvolumetric flask,dilute with water to volume,and mix (Solution B).Transfer 50.0mLof Solution Aand 5.0mLof Solution Bto a 500-mLvolumetric flask,dilute with water to volume,and mix to obtain a solution having concentrations of acetone and methanol of 0.050%and 0.005%(v/v),respectively.

Test preparation— Transfer 5.0g of Cefoxitin Sodium to a 50-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Transfer 3.0mLof the resulting solution to a 15-mLcentrifuge tube,cool in an ice-water bath for 2minutes,and add 3.0mLof 0.24Nhydrochloric acid while swirling vigorously.Centrifuge to obtain a clear solution (Test preparation).

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector,and contains a 1.8-m ×6.3-mm glass column containing support S2,and a pre-column packed with 60-to 80-mesh silane-treated glass beads.The injection port is maintained at 100,the columns are maintained at 110,the detector is maintained at 200,and nitrogen is used as the carrier gas at a flow rate of about 50mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the column efficiency determined from the acetone and methanol peaks is not less than 160and 200theoretical plates,respectively,the tailing factors for the acetone and methanol peaks are not more than 1.3and 2.3,respectively,and the relative standard deviation for replicate injections is not more than 5%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 2µL)of the Standard preparationand the Test preparationinto the chromatograph,record the chromatograms,and measure the acetone and methanol peak responses.Calculate the percentages of acetone and methanol in the Cefoxitin Sodium taken by the same formula: in which Pis the percentage (v/v)of acetone or methanol in the Standard preparation,and rUand rSare the acetone or methanol peak responses of the Test preparationand the Standard preparation,respectively:not more than 0.7%of acetone and 0.1%of methanol are found.

Mobile phase— Prepare a suitable mixture of water,acetonitrile,and glacial acetic acid (840:160:10),filter through a membrane filter (1µm or finer porosity),and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Phosphate buffer— Dissolve 1.0g of monobasic potassium phosphate and 1.8g of dibasic sodium phosphate in 900mLof water,adjust with phosphoric acid or 10Nsodium hydroxide to a pHof 7.1±0.1,dilute with water to make 1000mL,and mix.Filter through a membrane filter of 1µm or finer porosity.

Standard preparation— Dissolve an accurately weighed quantity of USP Cefoxitin RSin Phosphate bufferto obtain a solution having a known concentration of about 0.3mg per mL.[NOTE—Sonicate,if necessary,to dissolve the specimen.]Use this solution within 5hours.

Assay preparation— Transfer about 150mg of Cefoxitin Sodium,accurately weighed,to a 500-mLvolumetric flask,dissolve in and dilute with Phosphate bufferto volume,and mix.Use this solution within 5hours.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains 5-to 10-µm packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the column efficiency determined from the analyte peak is not less than 2800theoretical plates,the tailing factor for the analyte peak is not more than 1.5,and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in µg,of cefoxitin (C16H17N3O7S2)per mg of the Cefoxitin Sodium taken by the formula: in which Cis the concentration,in mg per mL,of USP Cefoxitin RSthe Standard preparation,Pis the potency,in µg per mg,of USP Cefoxitin RS,Wis the quantity,in mg,of Cefoxitin Sodium taken to prepare the Assay preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.