Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

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 45minutes.

Mobile phase— [NOTE—Prepare the Mobile phase one day prior to use.]Prepare a filtered and degassed mixture of water,methanol,tetramethylammonium hydroxide solution (1in 10),and phosphoric acid (700:300:14:3.5).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

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

Chromatographic system (see Chromatography á621ñ)—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 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.6for phenylpropanolamine and 1.0for 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 5µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in mg per mL,of USP Phenylpropanolamine Hydrochloride RSin the Standard preparation;and RUand RSare the peak response ratios of phenylpropanolamine and theophylline obtained from the Assay preparationand the Standard preparation,respectively.