A: Crush 1Tablet,boil it with 50mLof water for 5minutes,cool,and add 1or 2drops of ferric chloride TS:a violet-red color is produced.

B: Infrared Absorption á197Kñ—Prepare the test specimen as follows.Shake a quantity of finely powdered Tablets,equivalent to about 500mg of aspirin,with 10mLof alcohol for several minutes.Centrifuge the mixture.Pour off the clear supernatant,and evaporate it to dryness.Dry the residue in vacuum at 60for 1hour.

Apparatus 1: 100rpm.

Time: 90minutes,for Buffer stage.

Diluent— Prepare a mixture of 0.1Nhydrochloric acid and 0.20Mtribasic sodium phosphate (3:1),and adjust,if necessary,with 2Nhydrochloric acid or 2Nsodium hydroxide to a pHof 6.8±0.05.

Procedure— Determine the amount of C9H8O4dissolved by determining UVabsorbances at the wavelength of the isosbestic point of aspirin and salicylic acid (about 280nm in the Acid stage,and about 265nm in the Buffer stage)using a filtered portion of the solution under test,diluted,if necessary,with 0.1Nhydrochloric acid (analyzing the Acid stage)and with Diluent(analyzing the Buffer stage),in comparison with a Standard solution having a known concentration of USP Aspirin RSin the same medium.

Mobile phase and Diluting solution—Prepare as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Salicylic Acid RSin the Standard preparationprepared as directed in the Assay,to obtain a solution having a known concentration of about 0.015mg of salicylic acid per mL.

Test solution— Use the Stock solution,prepared as directed for Assay preparationin the Assay.

Chromatographic system— Use the Chromatographic systemdescribed in the Assay.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for salicylic acid and 1.0for aspirin;the resolution,R,between salicylic acid and aspirin is not less than 2.0;and the relative standard deviation of the salicylic acid peak responses is not more than 4.0%.

Procedure— Proceed as directed for Procedurein the Assay.Calculate the percentage of salicylic acid (C7H6O3)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 solution;QAis the quantity,in mg,of aspirin (C9H8O4)in the portion of Tablets taken,as determined in the Assay;and rUand rSare the peak responses of the salicylic acid peaks obtained from the Test solutionand the Standard solution,respectively:not more than 3.0%is found.

Mobile phase— Dissolve 2g of sodium 1-heptanesulfonate in a mixture of 850mLof water and 150mLof acetonitrile,and adjust with glacial acetic acid to a pHof 3.4.

Diluting solution— Prepare a mixture of acetonitrile and formic acid (99:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Aspirin RSin Diluting solutionto obtain a solution having a known concentration of about 0.5mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed quantity of the powder,equivalent to about 100mg of aspirin,to a suitable container.Add 20.0mLof Diluting solutionand about 10glass beads.Shake vigorously for about 10minutes,and centrifuge (Stock solution).Quantitatively dilute an accurately measured volume of the Stock solutionwith 9volumes of Diluting solution(Assay preparation).Retain the remaining portion of Stock solutionfor the test for Limit of free salicylic acid.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 280-nm detector and a 4.0-mm ×30-cm column containing packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not greater than 2.0;and the relative standard deviation 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.Calculate the quantity,in mg,of aspirin (C9H8O4)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Aspirin RSin the Standard preparation;and rUand rSare the peak responses of the aspirin peaks obtained from the Assay preparationand the Standard preparation,respectively.