Medium: 0.05Macetate buffer,prepared by mixing 2.99g of sodium acetate trihydrate and 1.66mLof glacial acetic acid with water to obtain 1000mLof solution having a pHof 4.50±0.05;500mL.

Apparatus 1: 50rpm.

Time: 45minutes.

Mobile phase and Chromatographic system—Prepare as directed in the Assay and limit of salicylic acid.

Standard preparation— Prepare a solution in Mediumcontaining known concentrations of about 0.002Amg of USP Aspirin RS,0.002Cmg of USP Caffeine RS,and 0.002Dmg of USP Dihydrocodeine Bitartrate RSper mL,A,C,and Dbeing the labeled amounts,in mg,of aspirin,caffeine,and dihydrocodeine bitartrate,respectively,in each Capsule.

Test preparation— Filter a portion of the solution under test.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Test preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantities,in mg,of aspirin (C9H8O4),caffeine (C8H10N4O2),and dihydrocodeine bitartrate (C18H23NO3·C4H6O6)dissolved by the same formula: in which Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation;and rUand rSare the peak responses of the relevant analyte obtained from the Test preparationand the Standard preparation,respectively.

Tolerances— Not less than 75%(Q)of the labeled amounts of C9H8O4,C8H10N4O2,and C18H23NO3·C4H6O6are dissolved in 45minutes.

Mobile phase— Dissolve 1g of sodium 1-pentanesulfonate and 2.3g of monobasic ammonium phosphate in 850mLof water.Add 150mLof acetonitrile,mix,degas,and adjust with phosphoric acid to a pHof 2.5.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluent— Prepare a mixture of water and acetonitrile (53:46),and adjust with phosphoric acid to a pHof 2.5.

Standard preparation— Prepare a solution in Diluentcontaining known concentrations of about 0.001Amg of USP Aspirin RS,0.001Cmg of USP Caffeine RS,and 0.001Dmg of USP Dihydrocodeine Bitartrate RSper mL,A,C,and Dbeing the labeled amounts,in mg,of aspirin,caffeine,and dihydrocodeine bitartrate,respectively,in each Capsule.[NOTE—Use this solution within 3hours.]

Standard salicylic acid preparation— Dissolve an accurately weighed quantity of USP Salicylic Acid RSin Diluentto obtain a solution having a known concentration of about 0.005Aµg per mL,Abeing the labeled amount,in mg,of aspirin per Capsule.[NOTE—Use this solution within 3hours.]

Resolution solution— Prepare a solution in Standard preparationcontaining about 0.0001Amg of USP Salicylic Acid RSper mL,Abeing the labeled amount,in mg,of aspirin in each Capsule.[NOTE—Use this solution within 3hours.]

Assay preparation— Transfer the contents of 10Capsules to a 500-mLvolumetric flask.Dilute with Diluentto volume,and mix.Transfer 5.0mLof this mixture to a 100-mLvolumetric flask,dilute with Diluentto volume,and mix.Centrifuge a portion of this mixture,and use the clear supernatant as the Assay preparation.[NOTE—Use this solution within 3hours.]

Chromatographic system— The liquid chromatograph is equipped with a 215-nm detector and a 4.6-mm ×15-cm column that contains packing L7.The flow rate is about 2mLper minute.Chromatograph the Resolution solution,and record the responses as directed for Procedure:the relative retention times are about 0.2for caffeine,0.3for dihydrocodeine,0.7for aspirin,and 1.0for salicylic acid;and the resolution,R,between the caffeine and dihydrocodeine peaks is not less than 2.5,between the dihydrocodeine and aspirin peaks is not less than 1.0,and between the aspirin and salicylic acid peaks is not less than 1.5.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%for each analyte.

Procedure— Separately inject equal volumes (about 10µL)of the Assay preparation,the Standard preparation,and the Standard salicylic acid preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantities,in mg,of aspirin (C9H8O4),caffeine (C8H10N4O2),and dihydrocodeine bitartrate (C18H23NO3·C4H6O6)in each Capsule taken by the same formula: in which Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation;and rUand rSare the responses of the corresponding analyte peaks of the Assay preparationand the Standard preparation,respectively.Calculate the percentage of salicylic acid in the Capsules taken by the formula: in which Cis the concentration,in µg per mL,of USP Salicylic Acid RSin the Standard salicylic acid preparation;Ais the labeled amount,in mg,of aspirin in each Capsule taken;and rUand rSare the salicylic acid peak responses obtained from the Assay preparationand the Standard salicylic acid preparation,respectively:not more than 3.0%is found.