A: Infrared Absorption 197K.

B: The RF value of the principal spot obtained from the Test preparation corresponds to that obtained from Solution A in the chromatogram prepared as directed in the test for Related compounds.

Standard preparations— Prepare a solution of USP Cinoxacin RS in a mixed solvent prepared by mixing equal volumes of chloroform, dimethylformamide, dimethyl sulfoxide, and nitromethane containing 5 mg per mL (Solution A). Prepare a second solution by diluting 1.0 volume of Solution A with the same mixed solvent to obtain 100 volumes of solution (Solution B).

Test preparation— Prepare a solution of Cinoxacin in the same mixed solvent used for the Standard preparations, containing 5 mg per mL.

Procedure— In a suitable chromatographic chamber arranged for thin-layer chromatography and lined with paper, place a volume of a solvent system consisting of a mixture of acetonitrile, water, and ammonium hydroxide (105:30:7.5) sufficient to develop the chromatogram, cover, and allow to equilibrate for 30 minutes. Apply 10-µL portions of Solution A, Solution B, and the Test preparation to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Dry the plate, and apply three additional 10-µL portions of each solution at the corresponding initial locations. Dry the plate thoroughly after each application, and develop the chromatogram until the solvent front has moved to the top of the plate. Remove the plate from the developing chamber, and allow the solvent to evaporate. View the plate under short- and long-wavelength UV light: the RF value of the principal spot obtained from the Test preparation corresponds to that obtained from Solution A, and no spot obtained from the Test preparation, other than the principal spot, is larger or more intense than the principal spot obtained from Solution B (1.0%).

Sodium borate solution— Dissolve 38.1 g of sodium borate in water to make 1000 mL.

Internal standard solution— Prepare an aqueous solution containing 2 mg of sulfanilic acid per mL and 5.0 mL of Sodium borate solution in each 100 mL.

Mobile phase— Dilute 100.0 mL of Sodium borate solution and 0.426 g of sodium sulfate with water to 1000 mL, mix, and degas. [note—The quantity of sodium sulfate may be varied to meet System suitability requirements, and to provide a suitable elution time.]

Standard preparation— Dissolve an accurately weighed quantity of USP Cinoxacin RS in Sodium borate solution to obtain a solution having a known concentration of about 1 mg per mL. Transfer 5.0 mL of this solution and 5.0 mL of the Internal standard solution to a 100-mL volumetric flask, dilute with water to volume, and mix. The Standard preparation contains about 50 µg of USP Cinoxacin RS per mL.

Assay preparation— Transfer about 50 mg of Cinoxacin, accurately weighed, to a 50-mL volumetric flask, dissolve in Sodium borate solution, dilute with the same solvent to volume, and mix. Transfer 5.0 mL of this solution and 5.0 mL of the Internal standard solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The chromatograph is equipped with a 254-nm detector and a 1.8-mm × 1-m column that contains packing L12. The flow rate is about 1 mL per minute. Chromatograph five replicate injections of the Standard preparation, and record the peak responses as directed under Procedure: the relative standard deviation is not more than 2.0%, the resolution factor between cinoxacin and sulfanilic acid is not less than 4.4, and the tailing factor for the cinoxacin peak is not more than 2.1.

Procedure— Separately inject equal volumes (about 1.0 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 2.2 for sulfanilic acid and 1.0 for cinoxacin. Calculate the quantity, in mg, of C12H10N2O5 in the portion of Cinoxacin taken by the formula: in which C is the concentration, in µg per mL, of USP Cinoxacin RS in the Standard preparation; and RU and RS are the ratios of the peak response of cinoxacin to the peak response of sulfanilic acid obtained from the Assay preparation and the Standard preparation, respectively.