Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 60minutes.

Mobile phase and Chromatographic system—Prepare as directed in the Assayunder Butalbital,Acetaminophen,and Caffeine Tablets.

Standard preparation— Prepare a solution in methanol having known concentrations of about 0.02Amg of USP Acetaminophen RSper mL,0.02Bmg of USP Butalbital RSper mL,and 0.02Cmg of USP Caffeine RSper mL,in which A,B,and Care the labeled amounts,in mg of acetaminophen,butalbital,and caffeine,respectively,per Capsule.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Procedure— Filter a portion of the solution under test through a filter of 10µm or finer porosity.Separately inject equal volumes (about 20µL)of the filtrate and the Standard preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantities,in mg,of butalbital (C11H16N2O3),acetaminophen (C8H9NO2),and caffeine (C8H10N4O2)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 corresponding analyte obtained from the solution under test and the Standard preparation,respectively.

Tolerances— Not less than 80%(Q)of the labeled amounts of C11H16N2O,C8H9NO2,and C8H10N4O2is dissolved in 60minutes.

Mobile phase ,Internal standard solution,Butalbital standard stock solution,Caffeine standard stock solution,Standard preparation,and Chromatographic system—Proceed as directed in the Assayunder Butalbital,Acetaminophen,and Caffeine Tablets.

Assay preparation— Remove,as completely as possible,the contents of not fewer than 20Capsules.Transfer an accurately weighed portion of the powder,equivalent to about the weight of the contents of 1Capsule,to a 200-mLvolumetric flask,add Internal standard solutionto volume,and mix.Sonicate for 15minutes,mix,and allow to cool and settle.Transfer 20.0mLof the clear supernatant to a 50-mLvolumetric flask,dilute with water to volume,and mix.Pass a portion of this solution through a filter of 0.5µm or finer porosity,discarding the first 5mLof the filtrate.Use the clear filtrate as the Assay preparation.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses for the major peaks.Calculate the quantities,in mg,of butalbital (C11H16N2O3),acetaminophen (C8H9NO2),and caffeine (C8H10N4O2)in the portion of Capsules taken by the formula: in which Dis the concentration,in mg per mL,of the appropriate USP Reference Standard in the Standard preparation;and RUand RSare the peak response ratios of the corresponding analyte to phenacetin obtained from the Assay preparationand the Standard preparation,respectively.