A: Transfer about 40 mg, accurately weighed, to a 250-mL volumetric flask, add 2 mL of 0.1 N hydrochloric acid to dissolve, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, add about 75 mL of water and 5.0 mL of 5 N sodium hydroxide, dilute with water to volume, and mix: the UV absorption spectrum of this solution, measured at 6 minutes, accurately timed, after the addition of the sodium hydroxide, exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Demeclocycline Hydrochloride RS, concomitantly measured, and the absorptivity, calculated on the anhydrous basis, at the wavelength of maximum absorbance at about 380 nm is between 103.5% and 111.3% of that of the USP Demeclocycline Hydrochloride RS, the potency of the Reference Standard being taken into account.

B: Transfer 40 mg, accurately weighed, to a 200-mL volumetric flask, add 100 mL of 0.1 N hydrochloric acid, shake to dissolve, dilute with 0.1 N hydrochloric acid to volume, and mix. Transfer 5.0 mL of this solution into each of two 50-mL volumetric flasks (Solutions 1 and 2). Prepare similar solutions of USP Demeclocycline Hydrochloride RS (Solutions 3 and 4). To Solutions 1 and 3, add 10 mL of 6 N hydrochloric acid, and to Solutions 2 and 4, add 10 mL of 3 N hydrochloric acid. Heat the four flasks in a water bath for 20 minutes, cool, dilute the contents with water to volume, and mix. Determine the absorbances of Solutions 1 and 3 at the wavelength of maximum absorbance at about 430 nm, with a suitable spectrophotometer, using Solutions 2 and 4, respectively, as the blanks. Determine the absorbances of Solutions 2 and 4 at the wavelength of maximum absorbance at about 368 nm, using Solutions 1 and 3, respectively, as the blanks. Calculate the ratio: in which WS is the weight, in mg, of USP Demeclocycline Hydrochloride RS taken, calculated on the dried basis; P is the potency, in µg per mg, of the USP Demeclocycline Hydrochloride RS; WU is the weight, in mg, of specimen taken, calculated on the anhydrous basis; and the final two parenthetic expressions are the absorbances of the four solutions at the wavelengths indicated by the subscripts for the specimen (U) and the Standard (S): the ratio is between 0.97 and 1.17.

(Official January 1, 2007)

Mobile phase— Transfer 80 g of tertiary butyl alcohol to a 1000-mL volumetric flask with the aid of 200 mL of water, add 100 mL of 0.2 M pH 9.0 phosphate buffer (prepared by mixing appropriate volumes of 0.2 M dibasic potassium phosphate and 0.2 M monobasic potassium phosphate), 150 mL of 0.02 M tetrabutylammonium hydrogen sulfate (adjusted with sodium hydroxide TS to a pH of 9.0), and 100 mL of 0.01 M edetate disodium (adjusted with sodium hydroxide TS to a pH of 9.0). Dilute with water to volume, mix, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621). Decreasing the amount of tertiary butyl alcohol increases the resolution.

Standard preparation— Dissolve an accurately weighed quantity of USP Demeclocycline Hydrochloride RS in 0.01 N hydrochloric acid to obtain a solution having a known concentration of about 1 mg per mL.

Assay preparation— Transfer about 45 mg of Demeclocycline, accurately weighed, to a 50-mL volumetric flask, dissolve in 0.01 N hydrochloric acid, dilute with 0.01 N hydrochloric acid to volume, and mix.

Resolution solution— Prepare a solution of USP Demeclocycline Hydrochloride RS in 0.01 N hydrochloric acid, and allow to stand for 3 hours.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column containing packing L21 and maintained at 60 ± 0.5. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the responses as directed for Procedure: the relative retention times are about 0.7 for epidemethylchlortetracycline and 1.0 for demeclocycline; and the resolution between the epidemethylchlortetracycline peak and the demeclocycline peak is not less than 3.0. Chromatograph the Standard preparation, and record the responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] 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 µg, of demeclocycline hydrochloride (C21H21ClN2O8·HCl) equivalent in each mg of the Demeclocycline taken by the formula: in which C is the concentration, in mg per mL, of USP Demeclocycline Hydrochloride RS in the Standard preparation; E is the demeclocycline hydrochloride equivalent, in µg per mg, of USP Demeclocycline Hydrochloride RS; W is the quantity, in mg, of the Demeclocycline taken; and rU and rS are the demeclocycline peak responses obtained from the Assay preparation and the Standard preparation, respectively.