A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

B: Accurately weigh a quantity of Capsule contents, equivalent to 10 mg of diazepam, place in a 50-mL centrifuge tube, and add 2 mL of acetone. Place the centrifuge tube in an ultrasonic bath for 5 minutes, remove from the ultrasonic bath, and centrifuge. Using 100 µL of the supernatant as the test solution, and 100 µL of a solution of USP Diazepam RS in acetone containing 5 mg per mL as the Standard solution, proceed as directed in Identification test B under Diazepam.

Medium: simulated gastric fluid TS, prepared without enzymes; 900 mL.

Apparatus 1: 100 rpm.

Times: 1, 4, 8, and 12 hours.

Mobile phase— Prepare a suitable degassed and filtered mixture of methanol and water (65:35). Make adjustments if necessary (see System Suitability under Chromatography 621).

Buffer solution— Dissolve 77.1 g of ammonium acetate in water to make 1000 mL of solution, and adjust with ammonium hydroxide to a pH of 8.7.

Standard solution— Dissolve an accurately weighed quantity of USP Diazepam RS in Medium, dilute quantitatively with Medium to obtain a solution having a known concentration of about 0.15 mg per mL, and mix. Transfer 2.0-, 5.0-, 8.0-, and 10.0-mL aliquots of this solution to separate 100-mL volumetric flasks, add Medium to volume, and mix. Pipet 1.0 mL of each solution and 1.0 mL of Buffer solution into individual small vials, mix, and allow to stand at room temperature for about 10 minutes.

Test solution— Wrap each Capsule in a coil made from a 10-cm piece of 18-gauge copper wire weighing approximately 750 mg, so that the wire encircles the Capsule 4 times. The Capsule enclosed in the coil remains at the bottom of the basket (it should not float). Pass a portion of the solution under test, obtained at each time interval, through a suitable filter having a 0.6-µm porosity. Pipet 1.0 mL of each solution and 1.0 mL of Buffer solution into individual small vials, mix, and allow to stand at room temperature for about 10 minutes.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and an 8-mm × 10-cm column that contains packing L1. The flow rate is about 5.0 mL per minute. Chromatograph the appropriate Standard solution, and record the peak responses as directed for Procedure: the tailing factor is not greater than 1.7; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Determine the amount of C16H13ClN2O dissolved from peak responses of diazepam obtained from the Test solution and the Standard solution.

Tolerances— The percentage of the labeled amount of C16H13ClN2O dissolved is within the range stated at each of the following times.

Mobile phase and Chromatographic system— Prepare as directed in the Assay under Diazepam.

Internal standard solution— Dissolve an accurately weighed quantity of USP Ethylparaben RS in methanol to obtain a solution having a known concentration of about 1.5 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Diazepam RS in methanol, quantitatively dilute with methanol to obtain a solution having a known concentration of about 1 mg per mL, and mix. Transfer 15.0 mL of this solution and 5.0 mL of Internal standard solution to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Assay preparation— Weigh and mix the contents of not fewer than 20 Capsules. Transfer an accurately weighed portion of the mixture, equivalent to about 15 mg of diazepam, to a 100-mL volumetric flask. Add 5.0 mL of Internal standard solution and about 45 mL of methanol. Shake by mechanical means for 30 minutes, dilute with methanol to volume, and mix. Centrifuge about 30 mL of this solution for 5 minutes, and filter.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The tailing factor for diazepam is not more than 2.0; and the relative standard deviation for the diazepam peak for replicate injections is not more than 2.0%. [note—For the purpose of identification, the relative retention times are about 0.5 for ethylparaben and 1.0 for diazepam.] Calculate the quantity, in mg, of diazepam (C16H13ClN2O) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Diazepam RS in the Standard preparation; and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.