Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

Mobile phase and Chromatographic system—Proceed as directed in the Assay.

Standard preparation— Prepare a solution in water containing about 0.0011A mg of USP Acetaminophen RS, 0.0011 AJ mg of USP Dichloralphenazone RS, and 0.0011 AJ¢ mg of USP Isometheptene Mucate RS per mL, A being the labeled amount, in mg, of acetaminophen per Capsule, J being the ratio of the labeled amount, in mg, of dichloralphenazone to the labeled amount, in mg, of acetaminophen per Capsule, and J¢ being the ratio of the labeled amount, in mg, of isometheptene mucate to the labeled amount, in mg, of acetaminophen per Capsule, and filter.

Test preparation— Filter about 20 mL of the solution under test through a glass fiber filter, discarding the first 15 mL of the filtrate.

Procedure— Proceed as directed for Procedure in the Assay except to inject 100 µL, instead of 10 µL. Calculate the quantity, in mg, of acetaminophen (C8H9NO2), dichloralphenazone (C15H18Cl6 N2O5), and isometheptene mucate [(C9H19N)2·C6H10O8] dissolved by the formula: in which C is the concentration, in mg per mL, of the appropriate USP Reference Standard in the Standard preparation; and rU and rS are the responses of the corresponding analyte peaks obtained from the Test preparation and the Standard preparation, respectively.

Tolerances— Not less than 65% (Q) of the labeled amounts of isometheptene mucate [(C9H19N)2·C6H10O8], dichloralphenazone (C15 H18Cl6N2O5), and acetaminophen (C8H9NO2) are dissolved after 60 minutes.

Mobile phase— Prepare a mixture of 0.07 M monobasic potassium phosphate, acetonitrile, 0.007 M sodium 1-decanesulfonate, and diethylamine (750:250:25:15). Adjust with phosphoric acid to a pH of 3.5. Filter and degas before use. Make adjustments if necessary (see System Suitability under Chromatography 621).

Chromatographic test solution— Empty the contents of 1 Capsule into a 100-mL volumetric flask, add about 80 mL of water, and swirl to dissolve. Dilute with water to volume, and mix. Pass a portion of this solution through a glass-fiber filter, discarding the first 5 mL of the filtrate. [note—Prepare this solution and chromatograph it as directed under Chromatographic system before preparing the Standard preparation and the Assay preparation.]

Standard preparation— Prepare a solution having known concentrations of about 3.25 mg of USP Acetaminophen RS, 3.25J mg of USP Dichloralphenazone RS, and 3.25J¢ mg of USP Isometheptene Mucate RS per mL, J being the ratio of the labeled amount, in mg, of dichloralphenazone to the labeled amount, in mg, of acetaminophen per Capsule, and J¢ being the ratio of the labeled amount, in mg, of isometheptene mucate to the labeled amount, in mg, of acetaminophen per Capsule.

Assay preparation— Transfer 20 Capsules, accurately counted, to a 2000-mL volumetric flask, add about 1900 mL of water, and heat on a steam bath until the Capsules disintegrate. While still warm, shake by mechanical means for 15 minutes, sonicate for 15 minutes, and allow to cool to ambient temperature. Dilute with water to volume, and mix. Pass a portion of this mixture through a glass-fiber filter, discarding the first 5 mL of the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a variable wavelength detector and a 4.6-mm × 25-cm column that contains 5-µm packing L7. The flow rate is about 1 mL per minute. Chromatograph 10 µL of the Chromatographic test solution, and record the chromatogram to confirm that all three analytes are detected and recorded acceptable levels of sensitivity. The wavelength and sensitivity settings are at 280 nm and 3.0 absorbance units full-scale until the acetaminophen peak has been recorded, then at 243 nm and 0.5 absorbance units full-scale until the dichloralphenazone peak has been recorded, and then at 190 nm and 0.5 absorbance units full-scale until the isometheptene mucate peak has been recorded. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections determined from each analyte peak 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), dichloralphenazone (C15H18Cl6N2O5), and isometheptene mucate [(C9H19N)2·C6H10O8)] in the portion of Capsules taken by the formula: in which C is the concentration, in mg per mL, of the appropriate USP Reference Standard in the Standard preparation; and rU and rS are the responses of the corresponding analyte peaks obtained from the Assay preparation and the Standard preparation, respectively.