A: Heat about 100mg of the Capsule contents with 10mLof water for several minutes,cool,and add 1drop of ferric chloride TS:a violet-red color is produced.

B: Shake a quantity of the contents of Capsules,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:the residue responds to Identificationtest Bunder Aspirin.

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: 100rpm.

Time: 30minutes.

Procedure— Determine the amount of C9H8O4dissolved from UVabsorbances at the wavelength of the isosbestic point of aspirin and salicylic acid at 265±2nm of filtered portions of the solution under test,suitably diluted with Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Aspirin RSin the same Medium.[NOTE—Prepare the Standard solution at the time of use.An amount of alcohol not to exceed 1%of the total volume of the Standard solution may be used to bring the Reference Standard into solution prior to dilution with Medium.]

Tolerances— Not less than 80%(Q)of the labeled amount of C9H8O4is dissolved in 30minutes.

Ferric chloride-urea reagent— Dissolve by swirling,without the aid of heat,60g of urea in a mixture of 8mLof ferric chloride solution (6in 10)and 42mLof 0.05Nhydrochloric acid.Adjust the resulting solution,if necessary,with 6Nhydrochloric acid to a pHof 3.2.

Standard preparation— Transfer 75.0mg of salicylic acid,previously dried over silica gel for 3hours and accurately weighed,to a 100-mLvolumetric flask,add chloroform to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,dilute with chloroform to volume,and mix.Transfer 10.0mLof this last solution to a 50-mLvolumetric flask containing 10mLof methanol,2drops of hydrochloric acid,and 10mLof a 1in 10solution of glacial acetic acid in ether,dilute with chloroform to volume,and mix.

Chromatographic column (see Chromatography á621ñ)— Proceed as directed under Column Partition Chromatography,packing a chromatographic tube with two segments of packing material.The lower segment is a mixture of 1g of Solid Supportand 0.5mLof 5Mphosphoric acid,and the upper segment is a mixture of 3g of Solid Supportand 2mLof freshly prepared Ferric chloride-urea reagent.

Test preparation— Weigh accurately a portion of the contents of the Capsules,as determined by the Assay,equivalent to 100mg of aspirin,mix with 10mLof chloroform by stirring for 3minutes,and then transfer to the chromatographic column with the aid of a few mLof chloroform.Pass 50mLof chloroform through the column,rinse the tip of the chromatographic tube with chloroform,and discard the eluate.Prepare as a receiver a 50-mLvolumetric flask containing 10mLof methanol and 2drops of hydrochloric acid,and elute any salicylic acid from the column by passing 10mLof a 1in 10solution of glacial acetic acid in ether that has been recently saturated with water,followed by 30mLof chloroform.Dilute the eluate with chloroform to volume,and mix.

Procedure— Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 306nm,with a suitable spectrophotometer,using as the blank a solvent mixture of the same composition as that used for the Standard preparation:the absorbance of the Test preparationdoes not exceed that of the Standard preparation(0.75%,calculated on the labeled aspirin content).

Standard preparation— Transfer about 50mg of USP Aspirin RS,accurately weighed,to a 50-mLvolumetric flask,add 0.5mLof glacial acetic acid,add chloroform to volume,and mix.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,dilute with a 1in 100solution of glacial acetic acid in chloroform to volume,and mix.The concentration of USP Aspirin RSis about 50µg per mL.

Chromatographic column— Proceed as directed under Column Partition Chromatography(see Chromatography á621ñ),packing a chromatographic tube with a mixture of 3g of Solid Supportand 2mLof freshly prepared sodium bicarbonate solution (1in 12).

Assay preparation— Remove,as completely as possible,the contents of not fewer than 20Capsules,and weigh accurately.Mix the combined contents,and transfer an accurately weighed quantity of the powder,equivalent to about 50mg of aspirin,to a 50-mLvolumetric flask containing 1mLof a 1in 50solution of hydrochloric acid in methanol,add chloroform to volume,and mix.Transfer 5.0mLof this solution to the column,wash with 5mLand then with 25mLof chloroform,and discard the washings.Elute into a 100-mLvolumetric flask with about 10mLof a 1in 10solution of glacial acetic acid in chloroform and then with about 85mLof a 1in 100solution of glacial acetic acid in chloroform,dilute with the latter solvent to volume,and mix.

Procedure— Without delay,concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 280nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in mg,of aspirin (C9H8O4)in the portion of Capsules taken by the formula: in which Cis the concentration,in µg per mL,of USP Aspirin RSin the Standard preparation;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.