A: Shake a quantity of Capsule contents, equivalent to about 300 mg of phendimetrazine tartrate, with about 50 mL of water, filter, and transfer the filtrate to a 200-mL separator. Add 3 mL of 12.5 N sodium hydroxide, and extract with two 50-mL portions of chloroform. Extract the combined chloroform extracts in a 250-mL separator with two 15-mL portions of 0.5 N hydrochloric acid, and evaporate the combined aqueous extracts on a steam bath to dryness. Dissolve the residue in 5 mL of acetone, and add 50 mL of anhydrous ether to the solution. On standing, phendimetrazine hydrochloride crystallizes out. Filter the precipitate, wash with anhydrous ether, and dry at 105: the crystals so obtained melt between 189 and 193, but the range between beginning and end of melting does not exceed 2.

B: A portion of Capsule contents responds to the test for Tartrate 191.

Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

pH 7.5 Phosphate buffer— Prepare a solution of 0.025 M monobasic potassium phosphate, and adjust with 1 N potassium hydroxide to a pH of 7.5.

Mobile phase— Prepare a suitable degassed and filtered mixture of acetonitrile and pH 7.5 Phosphate buffer (65:35).

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4-mm × 15-cm column that contains packing L15. The flow rate is about 1 mL per minute. Chromatograph three replicate injections of the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 3.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and a filtered aliquot of the solution under test into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of C12H17NO·C4H6O6 dissolved in comparison with a Standard solution of USP Phendimetrazine Tartrate RS, similarly prepared and chromatographed.

Tolerances— Not less than 70% (Q) of the labeled amount of C12H17NO·C4H6O6 is dissolved in 60 minutes.

Mobile phase— Dissolve 1.1 g of sodium 1-heptanesulfonate in 575 mL of water, add 400 mL of methanol, 25 mL of dilute acetic acid (14 in 100), and mix. Adjust with glacial acetic acid to a pH of 3.0 ± 0.1, if necessary. Filter through a 0.45-µm membrane filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluent— Prepare a mixture of water, methanol, and dilute acetic acid (14 in 100) (57.5:40:2.5).

Internal standard solution— Prepare a solution of salicylamide in Diluent having a concentration of about 0.1 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Phendimetrazine Tartrate RS in Internal standard solution, and dilute quantitatively with Internal standard solution to obtain a solution having a known concentration of about 0.7 mg of USP Phendimetrazine Tartrate RS per mL.

Assay preparation— Remove, as completely as possible, the contents of not fewer than 20 Capsules, and weigh accurately. Mix the combined contents, and transfer an accurately weighed quantity of the powder, equivalent to about 35 mg of phendimetrazine tartrate, to a 50-mL volumetric flask, add 25 mL of Internal standard solution, and sonicate for about 15 minutes. Cool the solution to room temperature, dilute with Internal standard solution to volume, mix, and filter through a 0.45-µm membrane filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 256-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 3.0, and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for salicylamide and 1.0 for phendimetrazine tartrate. Calculate the quantity, in mg, of C12H17NO·C4H6O6 in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Phendimetrazine Tartrate RS in the Standard preparation, and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.