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

Assay preparation— Transfer an accurately weighed portion of Solution, equivalent to about 20 mg of fluorouracil, to a 100-mL volumetric flask, dilute with water to volume, and mix. Quantitatively dilute a volume of this solution with water to obtain a concentration of 10 µg per mL.

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 peak responses for the major peaks. Calculate the quantity, in mg, of fluorouracil (C4H3FN2O2) in the portion of Solution taken by the formula: in which C is the concentration, in µg per mL, of USP Fluorouracil RS in the Standard preparation; and rU and rS are the fluorouracil responses obtained from the Assay preparation and the Standard preparation, respectively.