A: A portion of finely powdered Tablets meets the requirements for Identification test A under Phentermine Hydrochloride Capsules.

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 Tablets containing 15 mg of phentermine hydrochloride or less.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Ion-pair solution— Dissolve 1.1 g of sodium 1-heptanesulfonate in 1 L of water. Add 3.5 mL of glacial acetic acid, and mix.

Mobile phase— Prepare a filtered and degassed mixture of methanol and Ion-pair solution (21:19). Adjust with phosphoric acid to a pH of 2.5. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of USP Phentermine Hydrochloride RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration approximately equivalent to the Test solution.

Test solution— Use a filtered portion of the pooled sample under test.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 208-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Determine the amount, in mg, of phentermine hydrochloride (C10H15N·HCl) dissolved by the formula: in which V is the volume of dissolution media used per vessel; C is the concentration, in mg per mL, of USP Phentermine Hydrochloride RS in the Standard solution; and rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively.

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

Procedure for content uniformity— Proceed as directed in the Assay, except to prepare the Test preparations as follows. Transfer 1 Tablet to each of 10 suitable containers, add 1 mL of water and 10 mL of Internal standard solution to each, mix, sonicate for about 10 minutes after each Tablet has disintegrated, and filter.

Mobile phase— Prepare a suitably degassed solution containing 0.03% diethylamine in methanol. Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Prepare a solution of caffeine in Mobile phase having a final concentration of about 0.02 mg per mL.

Standard preparation— Transfer an accurately weighed amount of USP Phentermine Hydrochloride RS, equivalent to about 7.5 mg of phentermine hydrochloride, to a 10-mL volumetric flask. Add Internal standard solution to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 7.5 mg, to a suitable flask. Pipet 10.0 mL of Internal standard solution into the flask. Insert the stopper, mix, and sonicate for about 10 minutes. Pass through a filter having a 0.5-µm porosity.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.5 for caffeine and 1.0 for phentermine; the resolution, R, between caffeine and phentermine is not less than 4; the column efficiency determined from the analyte peak is not less than 2000 theoretical plates; and the relative standard deviation for replicate injections is not more than 2.0%.

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. Calculate the quantity, in mg, of phentermine hydrochloride (C10H15N·HCl) in the portion of Tablets 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 response ratios of phentermine to the internal standard obtained from the Assay preparation and the Standard preparation, respectively.