Identification—
Solution:
5 µg per mL.
Medium:
sulfuric acid in alcohol (1 in 360).
C:
Prepare a solution of it in alcohol containing about 0.2 mg per mL. Transfer 10 mL of this solution to a glass-stoppered, 100-mL graduated cylinder, add chloroform to volume, and mix. Apply 10 µL of the solution so obtained to a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel. Apply to the same plate 10 µL of a Standard solution of
USP Phenazopyridine Hydrochloride RS in the same medium having a known concentration of about 0.02 mg per mL. Develop the chromatogram in a solvent system consisting of a mixture of chloroform, ethyl acetate, and methanol (85:10:5) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber and allow it to dry. Locate the spots by spraying the plate lightly with 2 N hydrochloric acid: the
RF of the principal spot in the chromatogram of the test solution corresponds to that obtained from the Standard solution.
Water-insoluble substances—
Dissolve about 2 g, accurately weighed, in 200 mL of water, heat to boiling, then heat in a covered container on a steam bath for 1 hour. Filter through a tared, fine-porosity, sintered-glass crucible, wash thoroughly with water, and dry at 105
to constant weight: the weight of the residue does not exceed 0.1% of the weight of Phenazopyridine Hydrochloride taken.
Ordinary impurities 466—
Test solution—
Prepare a solution of it in alcohol having a concentration of 2.0 mg per mL.
Eluant:
a mixture of chloroform, ethyl acetate, and methanol (85:10:5).
Visualization—
Spray the plate with 5 N hydrochloric acid.
Assay—
Transfer about 100 mg of Phenazopyridine Hydrochloride, accurately weighed, to a 200-mL volumetric flask. Add about 100 mL of a mixture of sulfuric acid and alcohol (1 in 360), heat gently on a steam bath for 10 minutes, shake by mechanical means to dissolve, cool to room temperature, dilute with the alcoholic sulfuric acid to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with the alcoholic sulfuric acid to volume, and mix. Transfer 5.0 mL of the resulting solution to a 50-mL volumetric flask, dilute with the alcoholic sulfuric acid to volume, and mix. Concomitantly determine the absorbances of this solution and a Standard solution of
USP Phenazopyridine Hydrochloride RS in the same medium having a known concentration of about 5 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 390 nm, with a suitable spectrophotometer, using dilute alcoholic sulfuric acid (1 in 360) as the blank. Calculate the quantity, in mg, of C
11H
11N
5·HCl in the Phenazopyridine Hydrochloride taken by the formula:
20C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Phenazopyridine Hydrochloride RS in the Standard solution, and
AU and
AS are the absorbances of the solution of Phenazopyridine Hydrochloride and the Standard solution, respectively.
;)
