A: Shake a quantity of Soluble Powder with methanol to obtain a solution containing about 1 mg of oxytetracycline hydrochloride per mL. Filter if necessary to obtain a clear solution. 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 in the chromatogram of the Standard preparation, as obtained in the Assay.

(Official January 1, 2007)

Tetrabutylammonium hydrogen sulfate solution, Edetate disodium solution, pH 7.5 Phosphate buffer, Mobile phase, Standard preparation, System suitability solution, and Chromatographic system— Proceed as directed in the Assay under Oxytetracycline.

Assay preparation— Transfer an accurately weighed portion of the Soluble Powder, equivalent to about 100 mg of oxytetracycline hydrochloride, to a 500-mL volumetric flask, dilute with 0.01 N hydrochloric acid to volume, and mix. Pass a portion of this solution through a filter having a 0.5-µm or finer porosity. Use the filtrate as the Assay preparation.

Procedure— Proceed as directed for Procedure in the Assay under Oxytetracycline. Calculate the quantity, in g, of oxytetracycline hydrochloride (C22H24N2O9·HCl) in each g of Soluble Powder taken by the formula: in which 496.90 and 460.44 are the molecular weights of oxytetracycline hydrochloride and oxytetracycline, respectively; C is the concentration, in mg per mL, of USP Oxytetracycline RS in the Standard preparation; P is the assigned potency, in µg of oxytetracycline per mg, of USP Oxytetracycline RS; W is the weight, in g, of Soluble Powder taken to prepare the Assay preparation; and rU and rS are the oxytetracycline peak responses obtained from the Assay preparation and the Standard preparation, respectively.