Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C21H21N·HCl dissolved by employing UV absorption at the wavelength of maximum absorbance at about 285 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 Cyproheptadine Hydrochloride RS in the same Medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C21H21N·HCl is dissolved in 30 minutes.

(Official January 1, 2007)

Methanesulfonic acid solution— Prepare a solution of methanesulfonic acid in water (3:1000).

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile, isopropyl alcohol, and Methanesulfonic acid solution (20:15:65); while mixing adjust with triethylamine to a pH of 4.0 ± 0.05. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Cyproheptadine Hydrochloride RS in Mobile phase to obtain a solution having a known concentration of about 0.08 mg per mL.

Assay preparation— Transfer a number of Tablets, accurately weighed, equivalent to 80 mg of cyproheptadine hydrochloride, to a 1-liter volumetric flask, dissolve by sonication in 500 mL of Mobile phase for 15 minutes, and agitate for 30 minutes. Dilute with Mobile phase to volume, and mix. Pass through a filter having a 0.45-µm or finer porosity.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 285-nm detector and a 3.9-nm × 15-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.5; and the relative standard deviation for replicate injections 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 C21H21N·HCl in each of the Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Cyproheptadine Hydrochloride RS in the Standard preparation; N is the number of Tablets taken for the Assay preparation; and rU and rS are the cyproheptadine peak responses obtained from the Assay preparation and the Standard preparation, respectively.