A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: Place a number of Tablets, equivalent to about 1500 mg of ciprofloxacin, in a suitable flask containing about 750 mL of water, and sonicate for about 20 minutes. Dilute with water to 1000 mL, and mix. Centrifuge a portion of this suspension, and use the clear supernatant obtained as the test solution. Dissolve a quantity of USP Ciprofloxacin Hydrochloride RS in water to obtain a Standard solution containing 1.5 mg per mL. Proceed as directed for Identification test B under Ciprofloxacin Hydrochloride, starting with “Separately apply, as 1-cm bands, 5 µL each,” except to use 10 µL each of the test solution and the Standard solution: the specified result is obtained.

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of ciprofloxacin hydrochloride (C17H18FN3O3·HCl) dissolved by employing UV absorption at the wavelength of maximum absorbance at about 276 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Ciprofloxacin Hydrochloride RS in the same Medium.

Tolerances— An amount of ciprofloxacin hydrochloride (C17H18FN3O3·HCl) equivalent to not less than 80% (Q) of the labeled amount of ciprofloxacin (C17H18FN3O3) is dissolved in 30 minutes.

Diluent— Prepare a filtered and degassed mixture of 0.025 M phosphoric acid, previously adjusted (with triethylamine) to a pH of 2.0 ± 0.1, and acetonitrile (87:13).

Mobile phase— Prepare a filtered and degassed mixture of 0.025 M phosphoric acid, previously adjusted (with triethylamine) to a pH of 3.0 ± 0.1, and acetonitrile (87:13). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Quantitatively dissolve an accurately weighed quantity of USP Ciprofloxacin Hydrochloride RS in Diluent to obtain a solution having a known concentration of about 0.2 mg per mL.

Resolution solution— Dissolve a quantity of USP Ciprofloxacin Ethylenediamine Analog RS in the Standard preparation to obtain a solution containing about 0.05 mg per mL.

Assay preparation— Transfer 5 Tablets to a 500-mL volumetric flask, add about 400 mL of Diluent, and sonicate for about 20 minutes. Dilute with Diluent to volume, and mix. Quantitatively dilute an accurately measured volume of this solution, previously filtered through a 0.45-µm membrane filter, with Diluent to obtain a solution containing the equivalent of about 0.20 mg of ciprofloxacin per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 278-nm detector and a 4.6-mm × 25-cm column that contains packing L1 and is operated at 30 ± 1. The flow rate is about 1.5 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the retention time for ciprofloxacin is between 6.4 and 10.8 minutes; the relative retention times are about 0.7 for ciprofloxacin ethylenediamine analog and 1.0 for ciprofloxacin; and the resolution, R, between the ciprofloxacin ethylenediamine analog peak and the ciprofloxacin peak is not less than 6. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency, determined from the ciprofloxacin peak, is not less than 2500 theoretical plates; the tailing factor for the ciprofloxacin peak is not more than 2.0; and the relative standard deviation for replicate injections is not more than 1.5%.

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 peak areas for the major peaks. Calculate the quantity, in mg, of ciprofloxacin (C17H18FN3O3) in each Tablet taken by the formula: in which 331.34 and 367.81 are the molecular weights of ciprofloxacin and anhydrous ciprofloxacin hydrochloride, respectively; C is the concentration, in mg per mL, of USP Ciprofloxacin Hydrochloride RS in the Standard preparation, calculated on the anhydrous basis; L is the labeled quantity, in mg, of ciprofloxacin in each Tablet; D is the concentration, in mg per mL, of ciprofloxacin in the Assay preparation, based on the labeled quantity per Tablet and the extent of dilution; and rU and rS are the ciprofloxacin peak areas obtained from the Assay preparation and the Standard preparation, respectively.