Aspirin Suppositories

» Aspirin Suppositories contain not less than 90.0 percent and not more than 110.0 percent of the labeled amount of aspirin (C9H8O4).

Packaging and storage— Preserve in well-closed containers, in a cool place.

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USP Aspirin RS

Identification— Transfer a portion of the melted Suppositories obtained in the Assay, equivalent to about 1 g of aspirin, to a 125-mL conical flask. Add 20 mL of alcohol, and warm until completely disintegrated. Cool in an ice bath for 5 minutes, filter, and evaporate the filtrate to dryness: the residue responds to Identification tests A and B under Aspirin.

Limit of free salicylic acid—

Ferric chloride-urea reagent— To a mixture of 8 mL of ferric chloride solution (6 in 10) and 42 mL of 0.05 N hydrochloric acid add 60 g of urea. Dissolve the urea by swirling and without the aid of heat, and adjust the resulting solution, if necessary, by the addition of 6 N hydrochloric acid to a pH of 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 1 g of chromatographic siliceous earth and 0.5 mL of 5 M phosphoric acid. Directly above this layer, pack a similar mixture of about 3 g of chromatographic siliceous earth and 2 mL of 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 50 mg of aspirin, add 10 mL of chloroform, warm slightly, and stir until dissolved. With the aid of 5 mL of chloroform, transfer the mixture to the chromatographic adsorption column. Pass 50 mL of 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-mL volumetric flask containing 20 mL of methanol and 0.2 mL of hydrochloric acid by passing two 10-mL portions of a 1 in 10 solution of glacial acetic acid in water-saturated ether, and then 30 mL of 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 150 µg of salicylic acid per mL. Pipet 5 mL of this solution into a 50-mL volumetric flask containing 10 mL of methanol, 0.1 mL of hydrochloric acid, and 10 mL of a 1 in 10 solution 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 306 nm, 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 was saturated with water. ]

Chromatographic column— Uniformly pack a chromatographic tube, as described in the test for Limit of free salicylic acid for Procedure, with a mixture of about 3 g of chromatographic siliceous earth and 2 mL of sodium bicarbonate solution (1 in 12) prepared on the day of use.

Standard preparation— Transfer about 50 mg of USP Aspirin RS, accurately weighed, to a 50-mL volumetric flask, add 0.5 mL of glacial acetic acid, and add chloroform to volume. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, add a 1 in 100 solution 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 5 Suppositories, 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 50 mg of aspirin, to a 50-mL volumetric flask containing 1 mL of a 1 in 50 solution of hydrochloric acid in methanol, add 40 mL of chloroform, mix, and add chloroform to volume.

Procedure— Pipet 5 mL of the Assay preparation into the column, wash with 5 mL and then with 25 mL of chloroform, and discard the washings. Without delay, elute into a 100-mL volumetric flask with about 10 mL of a 1 in 10 solution of glacial acetic acid in chloroform, and then with about 85 mL of a 1 in 100 solution 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 preparation and the Standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 280 nm, 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 C is the concentration, in µg per mL, of USP Aspirin RS in the Standard preparation; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Clydewyn M. Anthony, Ph.D. Senior Scientific Liaison 1-301-816-8139	(SM22010) Monographs - Small Molecules 2
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org

USP35–NF30 Page 2248