A: Infrared Absorption 197M.

B: Ultraviolet Absorption 197U—

C: To 5 mL of a solution (1 in 100) add 1 mL of bromine water TS: the bromine color is discharged.

Isopropyl alcohol solution— Dilute 295 mL of isopropyl alcohol with water to 500 mL.

Buffer solution— To 55 g of sodium chloride in a 1-L volumetric flask add 500 mg of sodium citrate, 255 g of sodium acetate, and 300 mL of water. Shake to dissolve, and add 115 mL of glacial acetic acid. Cool to room temperature, add 300 mL of isopropyl alcohol, dilute with water to volume, and mix. The pH of the resulting solution is between 5.0 and 5.5.

Reagent blank— Pipet 15 mL of 1,2-dimethoxyethane into a flat-bottom, glass-joint, 500-mL flask, and proceed as directed for Test stock solution, beginning with “add the contents of a 15-mL vial of sodium biphenyl solution.”

Modified calomel reference electrode— Mix 70 mL of a freshly prepared saturated potassium chloride solution with 30 mL of isopropyl alcohol, fill the electrode with the clear supernatant, and allow the electrode to soak in the remainder of the solution for a minimum of 2 hours before using. Store the electrode immersed in the potassium chloride-isopropyl alcohol solution when not in use.

Standard stock solution— Accurately weigh 2.211 g of sodium fluoride, previously dried at 150 for 4 hours, transfer to a 1-L volumetric flask, and dissolve in about 200 mL of water. Add 1 mL of sodium hydroxide solution (1 in 25), dilute with water to volume, and mix. Store this solution in plastic containers. One mL is equivalent to 1 mg of fluoride.

Standard curve— Dilute 10.0 mL of Standard stock solution with water to 100 mL. Into each of four 100-mL volumetric flasks, pipet 0.8, 1.0, 1.2, and 1.6 mL, respectively, of the resulting solution. To each flask add 15 mL of Reagent blank, dilute with Buffer solution to volume, and mix. Use these dilutions, containing, respectively, 0.8, 1.0, 1.2, and 1.6 µg per mL, to construct the standard curve as follows. Determine the potentials of each solution as directed for Procedure. Plot the results of fluorine concentration, as the abscissa, in mg per 100 mL versus the potential, as the ordinate, on semilogarithmic graph paper, for each of the standards. Draw the best straight line through the plotted points.

Test stock solution— Place 200 mg of Fluorouracil, accurately weighed, in a 250-mL volumetric flask, add about 150 mL of 1,2-dimethoxyethane, shake by mechanical means to dissolve, dilute with the same solvent to volume, and mix. Pipet 15 mL of this solution into a flat-bottom, glass-joint, 500-mL flask, add the contents of a 15-mL vial of sodium biphenyl solution through a long-stem funnel to prevent splattering, swirl the flask gently, and cover with a watch crystal. Allow to stand at room temperature for 20 minutes, then cautiously add 50.0 mL of isopropyl alcohol while swirling the flask. Add 10.0 mL of 30 percent hydrogen peroxide and 4.0 mL of 1 N sodium hydroxide, and connect the flask to a water-cooled reflux condenser that has previously been cleaned with water and isopropyl alcohol and dried. Place the flask on a hot plate, set at about 245, and reflux for 1 hour. Cool to room temperature, rinse the condenser with 15 mL of Isopropyl alcohol solution, transfer the contents of the flask to a 250-mL volumetric flask using Isopropyl alcohol solution as a rinse, dilute with the same solvent to volume, and mix.

Test solution— Pipet 15 mL of the Test stock solution into a 100-mL volumetric flask, and dilute with Buffer solution to volume.

Procedure— Measure the potential, in mV, of the Test solution, with a suitable pH meter having a minimum reproducibility of ±0.2 mV, and equipped with a fluoride-specific ion electrode and a glass-sleeved Modified calomel reference electrode. When taking a measurement, immerse the electrodes into the solution, which has been transferred to a 150-mL plastic beaker, insert a suitable plastic-coated stirring bar, place the beaker on a magnetic stirrer, taking adequate precautions to prevent heat transfer, and stir for 2 minutes before reading. Dry the electrodes between measurements, taking care not to scratch the crystal surface of the specific ion electrode. Determine the quantity of fluorine, in mg per 100 mL of the Test solution, from the Standard curve. Multiply the quantity by the factor 138.9 to express the result as a percentage: not less than 13.9% and not more than 15.0% of fluorine, calculated on the dried basis, is found.

(Official January 1, 2007)

Mobile phase— Use degassed and filtered water.

Standard preparation— Dissolve an accurately weighed quantity of USP Fluorouracil RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 10 µg per mL.

Assay preparation— Transfer an accurately weighed quantity of about 20 mg of Fluorouracil to a 200-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Quantitatively dilute a known volume of this solution with water to obtain a solution having a concentration of about 10 µg per mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column containing packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 2500 theoretical plates, 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 C4H3FN2O2 in the portion of Fluorouracil 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 peak responses obtained from the Assay preparation and the Standard preparation, respectively.