Medium: water;900mL.

Apparatus 2: 100rpm.

Time: 60minutes.

Mobile phase,Internal standard solution,Solvent mixture,Standard stock solution,and Chromatographic system— Proceed as directed in the Assay.

Standard preparation— Transfer 20.0mLof Standard stock solution,3.0mLof Internal standard solution,and 20mLof water to a 50-mLvolumetric flask,mix,and allow to stand for about 30seconds.Dilute with Solvent mixtureto volume,and mix.Use within 8hours.

Test preparation— Transfer 20.0mLof a filtered portion of the solution under test to a 50-mLvolumetric flask,add 3.0mLof Internal standard solutionand 20mLof Solvent mixture,mix,and allow to stand for 30seconds.Dilute with Solvent mixtureto volume,and mix.

Procedure— Proceed as directed for Procedurein the Assay.Calculate the quantities,in mg,of acetaminophen (C8H9NO2),aspirin (C9H8O4),and caffeine (C8H10N4O2)dissolved by the formula: in which Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation;and RUand RSare the ratios of the peak responses of the corresponding analyte and internal standard peaks of the solution under test and the Standard preparation,respectively.

Tolerances— Not less than 75%(Q)of the labeled amounts of C8H9NO2,C9H8O4,and C8H10N4O2is dissolved in 60minutes.

Mobile phase and Solvent mixture—Prepare as directed in the Assay.

Standard preparation— Dissolve an accurately weighed quantity of USP Salicylic Acid RSin Solvent mixtureto obtain a solution having a known concentration of about 1mg per mL.Transfer 2.0mLof the resulting solution to a 100-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.This solution contains about 0.02mg of USP Salicylic Acid RSper mL.

Test preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 250mg of aspirin,to a 100-mLvolumetric flask.Add about 75mLof Solvent mixture,and shake by mechanical means for 30minutes.Dilute with Solvent mixtureto volume,and mix.

Chromatographic system— Proceed as directed for Chromatographic systemin the Assay,except to use a 302-nm detector.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the tailing factor is not more than 1.6;and the relative standard deviation for replicate injections is not more than 3.0%.

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 salicylic acid peaks.Calculate the percentage of salicylic acid in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Salicylic Acid RSin the Standard preparation;a is the quantity,in mg,of aspirin in the portion of Tablets taken,based on the labeled amount;and rUand rSare the salicylic acid peak responses of the Test preparationand the Standard preparation,respectively:not more than 3.0%is found.

Mobile phase— Prepare a suitable mixture of water,methanol,and glacial acetic acid (69:28:3).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of benzoic acid in methanol containing about 6mg per mL.

Solvent mixture— Prepare a mixture of methanol and glacial acetic acid (95:5).

Standard stock solution— Dissolve accurately weighed quantities of USP Acetaminophen RS,USP Aspirin RS,and USP Caffeine RSin Solvent mixtureto obtain a solution having known concentrations of about 0.25mg of USP Acetaminophen RSper mL,0.25Jmg of USP Aspirin RSper mL,and 0.25J¢mg of USP Caffeine RSper mL,Jbeing the ratio of the labeled amount,in mg,of aspirin to the labeled amount,in mg,of acetaminophen per Tablet;and J¢being the ratio of the labeled amount,in mg,of caffeine to the labeled amount,in mg,of acetaminophen per Tablet.

Standard preparation— Transfer 20.0mLof Standard stock solutionand 3.0mLof Internal standard solutionto a 50-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.This solution contains about 0.1mg of USP Acetaminophen RS,0.1Jmg of USP Aspirin RS,and 0.1J¢mg of USP Caffeine RSper mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 250mg of acetaminophen,to a 100-mLvolumetric flask.Add about 75mLof Solvent mixture,and shake by mechanical means for 30minutes.Dilute with Solvent mixtureto volume,and mix.Transfer 2.0mLof this solution and 3.0mLof Internal standard solutionto a 50-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.

Chromatographic system— The liquid chromatograph is equipped with a 275-nm detector and a 4.6-mm ×10-cm column that contains 5-µm packing L1,and is maintained at 45±1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the tailing factor for each analyte peak is not more than 1.2;the resolution,R,between any of the analyte and internal standard peaks is not less than 1.4;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.3for acetaminophen,0.5for caffeine,0.8for aspirin,1.0for benzoic acid,and 1.2for salicylic acid.Calculate the quantities,in mg,of acetaminophen (C8H9NO2),aspirin (C9H8O4),and caffeine (C8H10N4O2)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation;and RUand RSare the ratios of the peak responses of the corresponding analyte and internal standard peaks of the Assay preparationand the Standard preparation,respectively.