Packaging and storage—
Preserve in well-closed, light-resistant containers.
Clarity and color of solution—
A solution of 1.0 g in a mixture of 20 mL of water and 5 mL of 1 N sodium hydroxide is clear and not more deeply colored than pale yellow.
Identification—
B:
Add 5 mL of 3 N hydrochloric acid to about 0.1 g of Sulfapyridine, and boil gently for about 5 minutes. Cool in an ice bath, add 4 mL of sodium nitrite solution (1 in 100), dilute with water to 10 mL, and place the mixture in the ice bath for 10 minutes. To 5 mL of the cooled mixture add a solution of 50 mg of 2-naphthol in 2 mL of sodium hydroxide solution (1 in 10): an orange-red precipitate is formed, and it darkens on standing.
Acidity—
Digest 2.0 g with 100 mL of water at about 70
for 5 minutes, cool at once to about 20
, and filter. To 25.0 mL of the filtrate add 2 drops of phenolphthalein TS, and titrate with 0.10 N sodium hydroxide: not more than 0.20 mL is required for neutralization.
Heavy metals, Method II 
231
:
0.002%.
Organic volatile impurities, Method V 467:
meets the requirements.
Solvent—
Use dimethyl sulfoxide.
Assay—
Proceed with Sulfapyridine as directed under
Nitrite Titration 451. Each mL of 0.1 N sodium nitrite is equivalent to 24.93 mg of C
11H
11N
3O
2S.
;)
