Mobile phase— Prepare a mixture of water, methanol, and 0.2 M monobasic ammonium phosphate (33:5:3). Pass through a filter having a 0.5-µm or finer porosity, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Cefonicid Sodium RS in Mobile phase to obtain a solution having a known concentration of about 200 µg of cefonicid (C18H18N6O8S3) per mL.

Assay preparation 1 (where it is represented as being in a single-dose container)—Constitute Cefonicid 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 quantitatively dilute with Mobile phase to obtain a solution containing about 200 µg of cefonicid per mL.

Assay preparation 2 (where the label states the quantity of cefonicid in a given volume of constituted solution)—Constitute Cefonicid for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Quantitatively dilute an accurately measured volume of the constituted solution with Mobile phase to obtain a solution containing about 200 µg of cefonicid per mL.

Resolution solution— Dissolve a quantity of USP Cefonicid Sodium RS in Mobile phase to obtain a solution containing about 0.2 mg per mL. Heat on a steam bath for 30 minutes, and cool. This Resolution solution contains a mixture of cefonicid and desacetyl cefonicid.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation and the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between the cefonicid peak and the desacetyl cefonicid peak is not less than 1.1; the column efficiency determined from the analyte peak is not less than 1500 theoretical plates; the tailing factor for the analyte peak is not more than 2.0; and the relative standard deviation for replicate injections of the Standard preparation is not more than 2%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of cefonicid (C18H18N6O8S3) withdrawn from the container, or in the portion of constituted solution taken by the formula: in which L is the labeled quantity, in mg, of cefonicid in the container, or in the volume of constituted solution taken; D is the concentration, in µg per mL, of cefonicid in 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; C is the concentration, in µg per mL, of cefonicid in the Standard preparation; and rU and rS are the peak responses obtained from the relevant Assay preparation and the Standard preparation, respectively.