A: The retention time exhibited by clonidine hydrochloride in the chromatogram of the Assay preparation corresponds to that of clonidine hydrochloride in the chromatogram of the Standard preparation as obtained in the Assay.

B: Transfer a quantity of finely powdered Tablets, equivalent to about 1 mg of clonidine hydrochloride, to a separator containing 30 mL of water and 5 mL of 1 N sodium hydroxide. Swirl gently to dissolve the test specimen, and extract with 20 mL of chloroform. Allow the layers to separate, and filter the chloroform extract. Evaporate the filtrate to dryness, and dissolve the residue in 0.1 mL of methanol to obtain the test solution. Prepare a Standard solution in methanol containing 10 mg of USP Clonidine Hydrochloride RS per mL. Apply separately 2-µL portions of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of methanol and ammonium hydroxide (200:3) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Examine the plate under short-wavelength UV light: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Medium: 0.01 N hydrochloric acid; 500 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Using Dissolution Medium instead of Mobile phase to prepare the Standard clonidine hydrochloride stock solution and the Standard preparation, determine the amount of C9H9Cl2N3·HCl dissolved, employing the procedure set forth in the Assay, making any necessary modifications.

Tolerances— Not less than 75% (Q) of the labeled amount of C9H9Cl2N3·HCl is dissolved in 30 minutes.

(Official January 1, 2007)

Mobile phase— Dissolve 1.1 g of sodium 1-octanesulfonate in 500 mL of water, and add 500 mL of methanol and 1 mL of phosphoric acid. Mix, and adjust with 1 N sodium hydroxide to a pH of 3.0. Mix, filter through a 0.45-µm or finer porosity filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard clonidine hydrochloride stock solution— Dissolve an accurately weighed quantity of USP Clonidine Hydrochloride RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 100 µg per mL.

2 ,6-Dichloroaniline stock solution—Transfer about 12 mg of 2,6-dichloroaniline to a 100-mL volumetric flask, add Mobile phase to volume, and mix. Dilute an accurately measured volume of this solution quantitatively with Mobile phase to obtain 2,6-Dichloroaniline stock solution having a known concentration of about 12 µg per mL.

Standard preparation— Transfer 2.0 mL of Standard clonidine hydrochloride stock solution to a 200-mL volumetric flask, dilute with Mobile phase to volume, and mix. This solution contains about 1 µg of clonidine hydrochloride.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 0.1 mg of clonidine hydrochloride, to a 100-mL volumetric flask. Add about 60 mL of Mobile phase, shake by mechanical means for 15 to 30 minutes, dilute with Mobile phase to volume, and mix. Centrifuge a portion of this solution to obtain a clear solution (Assay preparation).

System suitability preparation— Transfer 2.0 mL of Standard clonidine hydrochloride stock solution and 20.0 mL of 2,6-Dichloroaniline stock solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 15-cm column that contains packing L7, which has been deactivated for basic compounds. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed under Procedure: the relative standard deviation for replicate injections is not more than 2.0% for the clonidine peak. Chromatograph the System suitability preparation, and record the peak responses as directed under Procedure: the column efficiency determined from the clonidine peak is not less than 3500 theoretical plates and the tailing factor for the clonidine peak is not more than 1.5. The relative retention times are about 0.5 for clonidine and 1.0 for 2,6-dichloroaniline.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 50 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 C9H9Cl2N3·HCl in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Clonidine Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.