Medium: water; 900 mL.

Apparatus 1: 100 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)

Mobile phase— [NOTE—Prepare the Mobile phase one day prior to use.] Prepare a filtered and degassed mixture of water, methanol, tetramethylammonium hydroxide solution (1 in 10), and phosphoric acid (700:300:14:3.5). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Prepare a solution of theophylline in methanol containing 0.1 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Phenylpropanolamine Hydrochloride RS in Internal standard solution to obtain a solution having a known concentration of about 3 mg per mL.

Assay preparation— Remove as completely as possible the contents of not fewer than 20 Capsules, weigh, and mix. Transfer an accurately weighed portion of the combined contents, equivalent to about 750 mg of phenylpropanolamine hydrochloride, to a suitable container. Add 250.0 mL of Internal standard solution, mix, sonicate for 30 minutes, allow to stand overnight, and filter.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L11. 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 0.6 for phenylpropanolamine and 1.0 for theophylline; the resolution, R, between phenylpropanolamine and theophylline is not less than 5.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 5 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 phenylpropanolamine hydrochloride (C9H13NO·HCl) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Phenylpropanolamine Hydrochloride RS in the Standard preparation; and RU and RS are the peak response ratios of phenylpropanolamine and theophylline obtained from the Assay preparation and the Standard preparation, respectively.