Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 60minutes.

Tolerances— Not less than 80%(Q)of the labeled amounts of butalbital (C11H16N2O3),caffeine (C8H10N4O2),and aspirin (C9H8O4)is dissolved in 60minutes.

Solvent— Add 1mLof phosphoric acid to 1000mLof methanol,and mix.

Standard preparation— Prepare a solution of USP Salicylic Acid RSin Solventhaving a known concentration of about 0.0012mg per mL.Use this solution promptly.

Test preparation— [NOTE—Perform this test on the same day the tablets are powdered.]Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 65mg of aspirin,to a 200-mLflask,add 100.0mLof Solvent,and shake by mechanical means for 15minutes.Filter a portion of this solution,discarding the first 15mLof the filtrate,and use the clear filtrate as the Test preparation.Use this solution within 20minutes after the addition of the Solvent.

Procedure— Immediately place the cell containing the solution under test in the cell compartment of a spectrophotofluorimeter,and allow to equilibrate for 2minutes.Concomitantly measure the intensities of the fluorescence of the Test preparationand the Standard preparationat 444nm,using an excitation wavelength of 305nm.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;ais the quantity,in mg,of aspirin in the portion of Tablets taken to prepare the Test preparation,based on the labeled amount;and IUand ISare the fluorescence intensity readings obtained from the Test preparationand the Standard preparation,respectively.[NOTE—If the intensity of the Test preparation greatly exceeds that of the Standard preparation,immediately transfer 5.0mLof the Test preparation to a 50-mLvolumetric flask,dilute with Solvent to volume,and mix.Immediately determine the intensity of this solution,and calculate the percentage of salicylic acid in the portion of Tablets taken by the formula: ]Not more than 3.0%is found.

0.01M Phosphate buffer ,pH2.5buffer,Mobile phase,Aspirin standard stock solution,Standard preparation,Salicylic acid solution,and Chromatographic system—Proceed as directed in the Assayunder Butalbital,Aspirin,and Caffeine Capsules.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 325mg of aspirin,to a 200-mLvolumetric flask,dilute with pH2.5bufferto volume,and sonicate for 30minutes.Pass a portion of this solution through a suitable filter of 0.5µm or finer porosity,and use the filtrate as the Assay preparation.Use this solution within 24hours.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,using the 277-nm detector to record the caffeine and aspirin peak areas and the 210-nm detector to record the butalbital peak areas,and measure the peak areas for the major peaks.Calculate the quantities,in mg,of butalbital (C11H16N2O3),aspirin (C9H8O4),and caffeine (C8H10N4O2)in the portion of Tablets 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 peak responses of the corresponding analyte obtained from the Assay preparationand the Standard preparation,respectively.Correct the amount of aspirin obtained for the amount of salicylic acid present taken by the formula: in which Ais the quantity,in mg,of aspirin in the portion of Tablets taken to prepare the Assay preparation;and Fis the percentage of salicylic acid obtained in the test for Limit of free salicylic acid.