A: Place an amount of finely powdered Tablets, equivalent to about 10 mg of clonazepam, in a 125-mL separator. Add 25 mL of water, shake for 2 minutes, and extract with two 40-mL portions of chloroform. Pass the extracts through anhydrous sodium sulfate, combine them, and evaporate at room temperature with the aid of a stream of nitrogen to dryness. Wash the residue with three 10-mL portions of solvent hexane: the IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Clonazepam RS.

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.

Medium: degassed water; 900 mL.

Apparatus 2: 75 rpm.

Time: 45 minutes.

Mobile phase— Prepare a filtered and degassed mixture of water, methanol, and acetonitrile (40:30:30). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Prepare a solution of USP Clonazepam RS in methanol having a known concentration of about 0.05 mg per mL. Quantitatively dilute a portion of this solution with Dissolution Medium to obtain a Standard solution having a known concentration similar to the expected concentration in the solution under test.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph replicate injections of the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 2.0%; and the tailing factor is not more than 2.0.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard solution and the solution under test into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity of C15H10ClN3O3 dissolved by comparison of the peak responses obtained from the Standard solution and the test solution.

Tolerances— Not less than 75% (Q) of the labeled amount of C15H10ClN3O3 is dissolved in 45 minutes.

Buffer solution, Mobile phase, Diluent, System suitability solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Clonazepam.

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 50 µL) of the Test preparation into the chromatograph, record the chromatogram, and measure the responses for all of the peaks. Calculate the percentage of each impurity in the portion of Tablets taken by the formula: in which P is the relative response factor, which is 2.45 for the peak with a relative retention time of 0.7 (if present), 1.84 for clonazepam related compound A, 0.94 for clonazepam related compound B, and 1 for all other impurities; ri is the peak response for each impurity obtained from the Test preparation; and rC is the peak response for clonazepam in the Test preparation: not more than 0.8% for the peak at relative retention time 0.7, not more than 0.4% of clonazepam related compound A, and not more than 1.0% of clonazepam related compound B are found; not more than 0.2% of any other impurity is found; and the sum of all other impurities is not more than 0.5%.

Buffer solution, Mobile phase, Diluent, Standard preparation, System suitability solution, and Chromatographic system— Proceed as directed in the Assay under Clonazepam.

Assay preparation— Weigh and finely powder not fewer than 10 Tablets. Transfer an accurately weighed amount of powder, equivalent to about 10 mg of clonazepam, to a 100-mL volumetric flask; dissolve, with sonication, in 75 mL of Diluent; cool to room temperature, dilute with Diluent to volume, mix, and filter, discarding the first few mL of the filtrate.

Procedure— 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 clonazepam (C15H10ClN3O3) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Clonazepam RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.