Identification—
A:
The UV absorption spectrum of the solution from the Capsule contents obtained in the Assay exhibits maximum absorption at the same wavelength as that of the Standard solution, and the two spectra are similar between 260 nm and 350 nm.
B:
Shake a portion of the contents of Capsules, equivalent to about 500 mg of flucytosine, with 10 mL of water. Filter, and to 2 mL of the filtrate add 1 mL of sodium pentacyanoaminoferrate reagent [prepared by dissolving 100 mg of sodium (tri)pentacyanoaminoferrate in 20 mL of sodium carbonate solution (1 in 100)] and 1 mL of 3 percent hydrogen peroxide: on standing, a darker green is produced than that produced by a blank.
Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 2:
75 rpm.
Time:
60 minutes.
Procedure—
Determine the amount of C
4H
4FN
3O dissolved by employing UV absorption at the wavelength of maximum absorbance at about 276 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 Flucytosine RS in the same
Medium.
Tolerances—
Not less than 80% (Q) of the labeled amount of C4H4FN3O is dissolved in 60 minutes.
Assay—
Weigh the contents of not fewer than 20 Capsules, and determine the average weight per Capsule. Mix the combined contents, and transfer an accurately weighed portion of the powder, equivalent to about 250 mg of flucytosine, to a 250-mL volumetric flask. Add about 50 mL of 0.1 N hydrochloric acid, shake by mechanical means for 30 minutes, then add 0.1 N hydrochloric acid to volume, mix, and filter, discarding the first 20 mL of the filtrate. Dilute 10 mL of the clear filtrate with 0.1 N hydrochloric acid to 250 mL. Dilute 10.0 mL of this solution with 0.1 N hydrochloric acid to 50 mL. Dissolve an accurately weighed quantity of
USP Flucytosine RS in 0.1 N hydrochloric acid, and dilute quantitatively and stepwise with the same solvent to obtain a Standard solution having a known concentration of about 8 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 285 nm, with a suitable spectrophotometer, using 0.1 N hydrochloric acid as the blank. Calculate the quantity, in mg, of flucytosine (C
4H
4FN
3O) in the portion of Capsule contents taken by the formula:
31.25C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Flucytosine RS in the Standard solution; and
AU and
AS are the absorbances of the solution from the Capsule contents and the Standard solution, respectively.
