Aspirin Suppositories
»Aspirin Suppositories contain not less than 90.0percent and not more than 110.0percent of the labeled amount of aspirin (C9H8O4).
Packaging and storage— Preserve in well-closed containers,in a cool place.
Identification— Transfer a portion of the melted Suppositories obtained in the Assay,equivalent to about 1g of aspirin,to a 125-mLconical flask.Add 20mLof alcohol,and warm until completely disintegrated.Cool in an ice bath for 5minutes,filter,and evaporate the filtrate to dryness:the residue responds to Identificationtests Aand Bunder Aspirin.
Limit of free salicylic acid—
Ferric chloride-urea reagent— To a mixture of 8mLof ferric chloride solution (6in 10)and 42mLof 0.05Nhydrochloric acid add 60g of urea.Dissolve the urea by swirling and without the aid of heat,and adjust the resulting solution,if necessary,by the addition of 6Nhydrochloric acid to a pHof 3.2.Prepare on the day of use.
Procedure— Insert a small pledget of glass wool above the stem constriction of a 20-×2.5-cm chromatographic tube,and uniformly pack with a mixture of about 1g of chromatographic siliceous earth and 0.5mLof 5Mphosphoric acid.Directly above this layer,pack a similar mixture of about 3g of chromatographic siliceous earth and 2mLof Ferric chloride-urea reagent.Transfer to a small beaker an accurately weighed portion of the cooled mass from the previously melted Suppositories obtained in the Assay,equivalent to 50mg of aspirin,add 10mLof chloroform,warm slightly,and stir until dissolved.With the aid of 5mLof chloroform,transfer the mixture to the chromatographic adsorption column.Pass 50mLof chloroform in several portions through the column,rinse the tip of the chromatographic tube with chloroform,and discard the eluate.If the purple zone reaches the bottom of the tube,discard the column,and repeat the test with a smaller quantity of melted Suppositories.
Elute the adsorbed salicylic acid into a 100-mLvolumetric flask containing 20mLof methanol and 0.2mLof hydrochloric acid by passing two 10-mLportions of a 1in 10solution of glacial acetic acid in water-saturated ether,and then 30mLof chloroform,through the column,and dilute the eluate with chloroform to volume.Dissolve a suitable,accurately weighed quantity of salicylic acid in chloroform to obtain a Standard solution containing 150µg of salicylic acid per mL.Pipet 5mLof this solution into a 50-mLvolumetric flask containing 10mLof methanol,0.1mLof hydrochloric acid,and 10mLof a 1in 10solution of glacial acetic acid in ether.Add chloroform to volume,and mix.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 306nm,using as the blank a solvent mixture of the same composition as that of the Standard solution:the absorbance of the solution from the Suppositories does not exceed that of the Standard solution (3.0%).
Assay— [NOTE—In this assay,use chloroform that recently saturated with water.]
Chromatographic column— Uniformly pack a chromatographic tube,as described in the test for Limit of free salicylic acidfor Procedure,with a mixture of about 3g of chromatographic siliceous earth and 2mLof sodium bicarbonate solution (1in 12)prepared on the day of use.
Standard preparation— Transfer about 50mg of USP Aspirin RS,accurately weighed,to a 50-mLvolumetric flask,add 0.5mLof glacial acetic acid,and add chloroform to volume.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,add a 1in 100solution of glacial acetic acid in chloroform to volume,and mix.
Assay preparation— Tare a small dish and glass rod,place in the dish not fewer than 5Suppositories,heat gently on a steam bath until melted,then stir,cool while stirring,and weigh.Transfer an accurately weighed portion of the mass,equivalent to about 50mg of aspirin,to a 50-mLvolumetric flask containing 1mLof a 1in 50solution of hydrochloric acid in methanol,add 40mLof chloroform,mix,and add chloroform to volume.
Procedure— Pipet 5mLof the Assay preparationinto the column,wash with 5mLand then with 25mLof chloroform,and discard the washings.Without delay,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.Without delay,concomitantly determine the absorbances of the eluted Assay preparationand the Standard preparationin 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 Suppositories taken by the formula:
C(AU/AS),
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.
Auxiliary Information— Staff Liaison:Clydewyn M.Anthony,Ph.D.,Scientist
Expert Committee:(PA2)Pharmaceutical Analysis 2
USP28–NF23Page 182
Phone Number:1-301-816-8139