Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of phenylpropanolamine hydrochloride dissolved, employing the procedure set forth in the Assay, making any necessary volumetric adjustments.

Tolerances— Not less than 75% (Q) of the labeled amount of C9H13NO·HCl is dissolved in 45 minutes.

(Official January 1, 2007)

Solvent A— Dissolve 1.9 g of sodium 1-hexanesulfonate in 700 mL of water, add 50 mL of 1 M monobasic sodium phosphate and 20 mL of 0.25 N triethylammonium phosphate (prepared by mixing 500 mL of a solution containing 25.3 g of triethylamine and 500 mL of a solution containing 9.6 g of phosphoric acid), and mix. Dilute with water to 1 liter, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Solvent A and methanol (100:82). Make adjustments if necessary (see Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Phenylpropanolamine Hydrochloride RS in methanol, and dilute quantitatively with methanol to obtain a solution having a known concentration of about 375 µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 750 mg of phenylpropanolamine hydrochloride, to a 200-mL volumetric flask. Add about 150 mL of methanol, and sonicate for about 10 minutes. Dilute with methanol to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with methanol to volume, mix, and filter.

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 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor for the analyte peak is not more than 2.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 70 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 C9H13NO·HCl in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Phenylpropanolamine Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.