Packaging and storage—
Preserve in well-closed, light-resistant containers.
Identification—
Extract a quantity of powdered Tablets, equivalent to about 1 g of sulfisoxazole, with 50 mL of alcohol by boiling on a steam bath for 3 minutes, then immediately filter into a beaker. Allow to stand until a quantity of fine, needle-like crystals form. Cool, filter off the crystals, recrystallize from a small volume of alcohol, and dry at 105
: the crystals respond to
Identification test
A under
Sulfisoxazole.
Dissolution 
711
—
Medium:
dilute hydrochloric acid (1 in 12.5); 900 mL.
Apparatus 1:
100 rpm.
Time:
30 minutes.
Procedure—
[NOTE—Because of the pH-dependent nature of the UV absorption spectrum, prepare the standard and specimen solutions in the same strength of acid at approximately equal concentrations.
] Determine the amount of C
11H
13N
3O
3S dissolved from UV absorbances at the wavelength of maximum absorbance at about 267 nm of filtered portions of the solution under test, suitably diluted with water, if necessary, in comparison with a Standard solution having a known concentration of
USP Sulfisoxazole RS in the same medium.
Tolerances—
Not less than 70% (Q) of the labeled amount of C11H13N3O3S is dissolved in 30 minutes.
Assay—
Weigh and finely powder not less than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 800 mg of sulfisoxazole, transfer to a 250-mL conical flask, and proceed as directed in the
Assay under
Sulfisoxazole, beginning with “add 50 mL of dimethylformamide.”
