A: Shake a suitable quantity of Capsule contents with methanol to obtain a solution containing 1mg of doxycycline per mL,and filter.Using the filtrate as the Test solution,proceed as directed for Method IIunder Identification—Tetracyclines á193ñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that of the Standard preparationas obtained in the Assay.

Medium: 0.01Nhydrochloric acid;900mL.

Apparatus 2: 75rpm.

Time: 60minutes.

Procedure— Determine the amount of C22H24N2O8dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 268nm 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 RSin the same Medium.

Tolerances— Not less than 85%(Q)of the labeled amount of C22H24N2O8is dissolved in 60minutes.

Mobile phase,Diluent,Resolution solution,Standard preparation,and Chromatographic system— Proceed as directed in the Assayunder 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 20Capsules,and weigh accurately.Mix the combined contents,and transfer an accurately weighed portion of the powder,equivalent to about 100mg of doxycycline,to a 100-mLvolumetric flask.Add 20mLof 0.1Nhydrochloric acid,sonicate for 5minutes,shake for 15minutes,dilute with Diluentto volume,and mix.Filter a portion of this solution through a filter of 0.5µm or finer porosity,and use the filtrate as the Assay preparation.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in mg per mL,of USP Doxycycline Hyclate RSin the Standard preparation,Pis the designated potency,in µg of doxycycline per mg,of USP Doxycycline Hyclate RS,and rUand rSare the doxycycline peak responses obtained from the Assay preparationand the Standard preparation,respectively.