A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: Transfer a portion of Suppositories, equivalent to about 20 mg of acetaminophen, to a beaker, add 20 mL of methanol, and heat on a steam bath until melted. Remove the beaker from the steam bath, allow to cool with occasional stirring, and filter: the clear filtrate (test solution) responds to the Thin-layer Chromatographic Identification Test 201, a solvent system consisting of a mixture of methylene chloride and methanol (4:1) being used.

(Official January 1, 2007)

Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Acetaminophen Capsules.

Assay preparation— Tare a small dish and a 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 100 mg of acetaminophen, to a separator, add 30 mL of solvent hexane, and mix to dissolve. Add 30 mL of water, shake gently, and allow the phases to separate. [NOTE—If an emulsion forms, allow sufficient time for it to separate.] Transfer the aqueous layer to a 200-mL volumetric flask, wash the solvent hexane in the separator with three 30-mL portions of water, adding the washings to the volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of this solution to a 250-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass a portion of this solution through a filter having a 0.5-µm or finer porosity, discarding the first 10 mL of the filtrate. Use the clear filtrate as the Assay preparation.

Procedure— Proceed as directed for Procedure in the Assay under Acetaminophen Capsules. Calculate the quantity, in mg, of acetaminophen (C8H9NO2) in each Suppository taken by the formula: in which C is the concentration, in mg per mL, of USP Acetaminophen RS in the Standard preparation; A is the average weight, in mg, of each Suppository taken; W is the weight, in mg, of the Suppository mass taken; and rU and rS are the acetaminophen peak responses obtained from the Assay preparation and the Standard preparation, respectively.