Medium: water;900mL.

Apparatus 2: 50rpm.

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.

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

Mobile phase— Prepare a filtered and degassed mixture of Solvent Aand methanol (100:82).Make adjustments if necessary (see Chromatography á621ñ).

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

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

Chromatographic system(see Chromatography á621ñ)— 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 1.5mLper 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 70µL)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 C9H13NO·HCl in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Phenylpropanolamine Hydrochloride RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.