A: Stir a portion of the Capsule contents in acetone to prepare a solution containing about 1 mg of phentermine hydrochloride per mL, and filter using an acetone resistant filter. Transfer 1 mL of the clear filtrate to a mortar containing about 200 mg of potassium bromide, triturate with a pestle, and air-dry to allow the acetone to evaporate. Place in an oven at 125 for 30 minutes to dry the mixture: the IR absorption spectrum of a potassium bromide dispersion prepared from the residue exhibits maxima only at the same wavelengths as that of a similar preparation of USP Phentermine Hydrochloride 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: water; 900 mL. Use 500 mL for Capsules containing 15 mg of phentermine hydrochloride or less.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C10H15N·HCl dissolved, employing the procedure set forth in the Assay, making any necessary modifications including concentration of the analyte in the volume of test solution taken.

Tolerances— Not less than 75% (Q) of the labeled amount of C10H15N·HCl is dissolved in 45 minutes.

(Official January 1, 2007)

Mobile phase— Dissolve 1.1 g of sodium 1-heptanesulfonate in 575 mL of water. Add 25 mL of dilute glacial acetic acid (14 in 100) and 400 mL of methanol. Adjust dropwise, if necessary, with glacial acetic acid to a pH of 3.3 ± 0.1. Filter through a 0.5-µm membrane filter. The volume of methanol may be adjusted to provide a suitable retention time for phentermine hydrochloride (about 8 minutes).

Standard preparation— Using an accurately weighed quantity of USP Phentermine Hydrochloride RS, prepare a solution in 0.04 M phosphoric acid having a known concentration of about 0.4 mg per mL.

Assay preparation— Remove, as completely as possible, the contents of not fewer than 20 Capsules, and weigh. Transfer an accurately weighed portion of the mixed powder, equivalent to about 20 mg of phentermine hydrochloride, to a 50-mL volumetric flask. Add 40 mL of 0.04 M phosphoric acid, and sonicate for 15 minutes. Dilute with 0.04 M phosphoric acid to volume, and mix. Filter through a 0.5-µm membrane filter, discarding the first few mL of the filtrate.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph three replicate injections of the Standard preparation, and record the peak response as directed for Procedure: the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph by means of a suitable sampling valve, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C10H15N·HCl in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Phentermine Hydrochloride RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.