Packaging and storage—
Preserve in well-closed, light-resistant containers.
Identification—
A:
Place a quantity of finely powdered Tablets, equivalent to about 100 mg of sulfamethoxazole, in a 50-mL centrifuge tube, and proceed as directed for
Identification test
A under
Sulfamethoxazole Oral Suspension, beginning with “add 5 mL of ammonium hydroxide.”
B:
To a portion of finely powdered Tablets, equivalent to about 100 mg of sulfamethoxazole, add 2 mL of hydrochloric acid, 3 mL of sodium nitrite solution (1 in 100), and 1 mL of sodium hydroxide solution (1 in 10) containing 10 mg of 2-naphthol: a red-orange precipitate is formed.
Dissolution 
711
—
Medium:
dilute hydrochloric acid (7 in 100); 900 mL.
Apparatus 1:
100 rpm.
Time:
30 minutes.
Procedure—
Determine the amount of C
10H
11N
3O
3S dissolved from UV absorbances at the wavelength of maximum absorbance at about 265 nm of 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 Sulfamethoxazole RS in the same medium.
Tolerances—
Not less than 80% (Q) of the labeled amount of C10H11N3O3S 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 500 mg of sulfamethoxazole, dissolve in a mixture of 20 mL of glacial acetic acid and 40 mL of water, and add 15 mL of hydrochloric acid. Cool to 15
, and titrate immediately with 0.1
M sodium nitrite VS, determining the endpoint potentiometrically using a calomel-platinum electrode system. Each mL of 0.1
M sodium nitrite is equivalent to 25.33 mg of C
10H
11N
3O
3S.
