A: Infrared Absorption 197M.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that observed in the chromatogram of the Standard preparation obtained as directed in the Assay.

Mobile phase— Prepare a filtered and degassed mixture of 0.1 M phosphoric acid, methanol, acetonitrile, and glacial acetic acid (1700:105:105:100). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 20 mg of USP Cefotetan RS, accurately weighed, to a 100-mL volumetric flask, add 5 mL of methanol, swirl for several minutes, add 5 mL of acetonitrile, and swirl until dissolved. Dilute with water to volume, and mix.

Resolution solution— Place 10 mL of Standard preparation in a glass-stoppered flask containing a few mg of magnesium carbonate, and sonicate for 10 minutes. If the solution is not turbid, add a few more mg of magnesium carbonate, and repeat the sonication. Filter the turbid solution through a filter of 0.5 µm or finer porosity. Collect the clear filtrate, and use as the Resolution solution.

Assay preparation— Using a suitable quantity of Cefotetan, accurately weighed, proceed as directed for Standard preparation.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph 20 µL of the Resolution solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.75 for cefotetan and 1.0 for cefotetan tautomer; and the resolution between the cefotetan peak and the cefotetan tautomer peak is not less than 2.0. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1500 theoretical plates, the tailing factor is not more than 1.5, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas of the responses for the major peaks. Calculate the quantity, in µg, of cefotetan (C17H17N7O8S4) in each mg of the Cefotetan taken by the formula: in which C is the concentration, in mg per mL, of USP Cefotetan RS in the Standard preparation; P is the designated potency, in µg of cefotetan (C17H17N7O8S4) per mg, of USP Cefotetan RS; M is the weight, in mg, of Cefotetan taken to prepare the Assay preparation; and rU and rS are the cefotetan peak responses obtained from the Assay preparation and the Standard preparation, respectively.