Medium: pH4.5acetate buffer,prepared as directed in the Dissolutiontest under Propoxyphene Hydrochloride,Aspirin,and Caffeine Capsules;500mL.

Apparatus 1: 100rpm.

Time: 60minutes.

Diethylamine phosphate buffer,Mobile phase,andChromatographic system— Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Propoxyphene Napsylate RSin Dissolution Mediumto obtain a solution having a known concentration of about 0.1mg per mL.

Test solution— Quantitatively dilute a filtered portion of the solution under test with Dissolution Mediumto obtain a solution having a concentration of about 0.1mg of propoxyphene napsylate per mL.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the areas for the propoxyphene peaks.Calculate the quantity,in mg,of C22H29NO2·C10H8O3S·H2Odissolved by the formula: in which 565.72and 547.72are the molecular weights of propoxyphene napsylate and anhydrous propoxyphene napsylate,respectively;Cis the concentration,in mg per mL,of USP Propoxyphene Napsylate RSin the Standard solution;Dis the dilution factor used to prepare the Test solution;and rUand rSare the peak responses obtained from the Test solutionand the Standard solution,respectively.

Tolerances— Not less than 75%(Q)of the labeled amount of C22H29NO2·C10H8O3S·H2Ois dissolved in 60minutes.

Diethylamine phosphate buffer— Mix 5.0mLof diethylamine with 995mLof water,and adjust with phosphoric acid to a pHof 3.2.

Diluent— Prepare a mixture of Diethylamine phosphate bufferand acetonitrile (4:1).

Mobile phase— Prepare a mixture of Diethylamine phosphate bufferand acetonitrile (3:2).Sonicate for 15minutes,and pass through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Propoxyphene Napsylate RSin Diluentto obtain a solution having a known concentration of about 0.1mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 5Tablets,to a 1000-mLvolumetric flask.Dissolve in and dilute with Diluentto volume,and mix.Further dilute 10.0mLof the resulting solution with Diluent,mix,and filter or centrifuge to obtain a clear solution having a concentration of about 0.1mg per mL.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 217-nm detector and a 3.9-mm ×30-cm column containing packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the tailing factor is not more than 1.5;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the propoxyphene peaks.Calculate the quantity,in mg,of propoxyphene napsylate (C22H29NO2·C10H8O3S·H2O)in the portion of the Tablets taken by the formula: in which 565.72and 547.72are the molecular weights of propoxyphene napsylate monohydrate and anhydrous propoxyphene napsylate,respectively;Cis the concentration,in mg per mL,of USP Propoxyphene Napsylate RSin the Standard preparation;Dis the dilution factor used to prepare the Assay preparation;and rUand rSare the responses obtained from the Assay preparationand the Standard preparation,respectively.