H2SeO3 128.97

Selenium dioxide, monohydrated.
Selenious acid [7783-00-8].

Packaging and storage— Preserve in tight containers.

Identification—

Residue on ignition 281: not more than 1.0 mg, from 10.0 g (0.01%).

Insoluble matter— Dissolve 1 g in 5 mL of water: it dissolves completely and the solution is clear.

Selenate and sulfate— Dissolve about 0.5 g in 10 mL of water, add 0.1 mL of hydrochloric acid and 1 mL of barium chloride TS, and mix: no turbidity or precipitate is formed in 10 minutes.

Organic volatile impurities, Method I 467: meets the requirements.

Residual solvents 467: meets the requirements.

Assay— Transfer about 100 mg of Selenious Acid, accurately weighed, to a suitable glass-stoppered flask, and dissolve in 50 mL of water. Add 10 mL of potassium iodide solution (3 in 10) and 5 mL of hydrochloric acid, mix, insert the stopper in the flask, and allow to stand for 10 minutes. Add 50 mL of water and 3 mL of starch TS, and titrate with 0.1 N sodium thiosulfate VS until the solution is colorless, then titrate with 0.1 N iodine VS to a blue endpoint. Subtract the volume of 0.1 N iodine from the volume of 0.1 N sodium thiosulfate to obtain the volume of 0.1 N sodium thiosulfate equivalent to selenious acid. Each mL of 0.1 N sodium thiosulfate is equivalent to 3.225 mg of H2SeO3.

Expert Committee : (MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine

USP29–NF24 Page 1957

Phone Number : 1-301-816-8251