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: Triturate an amount of the contents of the Capsules, equivalent to about 50 mg of acetaminophen, with 50 mL of methanol, 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.

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C8H9NO2 dissolved from UV absorption at the wavelength of maximum absorbance at about 249 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Acetaminophen RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C8H9NO2 is dissolved in 45 minutes.

(Official January 1, 2007)

Mobile phase— Prepare a suitable degassed mixture of water and methanol (3:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Acetaminophen RS in Mobile phase to obtain a solution having a known concentration of about 0.01 mg per mL.

Assay preparation— Weigh the contents of not fewer than 20 Capsules, and calculate the average weight of the contents of each Capsule. Mix the combined contents of the Capsules, and transfer an accurately weighed portion, equivalent to about 100 mg of acetaminophen, to a 200-mL volumetric flask. Add about 100 mL of Mobile phase, and shake by mechanical means for 10 minutes. 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.

Chromatographic system— The liquid chromatograph is equipped with a 243-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the responses as directed for Procedure: the column efficiency is not less than 1000 theoretical plates; the tailing factor is not more than 2; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of acetaminophen (C8H9NO2) in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of USP Acetaminophen RS in the Standard preparation; and rU and rS are the acetaminophen peak responses obtained from the Assay preparation and the Standard preparation, respectively.