A: Shake a suitable quantity of Capsule contents with methanol to obtain a solution containing 1 mg of doxycycline per mL, and filter. Using the filtrate as the Test solution, proceed as directed for Method II under Identification—Tetracyclines 193.

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

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 75 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C22H24N2O8 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 268 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 Doxycycline Hyclate RS in the same Medium.

Tolerances— Not less than 85% (Q) of the labeled amount of C22H24N2O8 is dissolved in 60 minutes.

(Official January 1, 2007)

Mobile phase, Diluent, Resolution solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Doxycycline Hyclate.

NOTE—Throughout the following sections, protect the Standard preparation, the Assay preparation, and the stock solutions used in their preparation, from light.

Assay preparation— Remove, as completely as possible, the contents of not less than 20 Capsules, and weigh accurately. Mix the combined contents, and transfer an accurately weighed portion of the powder, equivalent to about 100 mg of doxycycline, to a 100-mL volumetric flask. Add 20 mL of 0.1 N hydrochloric acid, sonicate for 5 minutes, shake for 15 minutes, dilute with Diluent to volume, and mix. Filter a portion of this solution through a filter of 0.5 µm or finer porosity, and use the filtrate as the Assay preparation.

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 responses for the major peaks. Calculate the quantity, in mg, of doxycycline (C22H24N2O8) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Doxycycline Hyclate RS in the Standard preparation, P is the designated potency, in µg of doxycycline per mg, of USP Doxycycline Hyclate RS, and rU and rS are the doxycycline peak responses obtained from the Assay preparation and the Standard preparation, respectively.