Selenious Acid
(se lee' nee us as' id).
H2SeO3 128.97 Selenium dioxide, monohydrated; Selenious acid [7783-00-8]. DEFINITION
Selenious Acid contains NLT 93.0% and NMT 101.0% of H2SeO3.
IDENTIFICATION
• A.
Sample:
50 mg
Analysis:
Dissolve the Sample in 5 mL of water. Add 100 mg of sodium bicarbonate, and mix.
Acceptance criteria:
Gas bubbles develop.
• B.
Sample:
50 mg
Analysis:
Dissolve the Sample in 5 mL of 0.1 N hydrochloric acid. Add 50 mg of stannous chloride.
Acceptance criteria:
A curdy tan-orange precipitate is formed.
ASSAY
• Procedure
Sample solution:
Transfer 100 mg to a suitable glass-stoppered flask, and dissolve in 50 mL of water.
Analysis:
Add 10 mL of a 300-mg/mL potassium iodide solution and 5 mL of hydrochloric acid to the Sample solution, and mix. Insert the stopper in the flask, and allow to stand for 10 min. Add 50 mL of water and 3 mL of starch TS. 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.
Acceptance criteria:
93.0%101.0%
IMPURITIES
• Insoluble Matter
Sample:
1 g
Analysis:
Dissolve the Sample in 5 mL of water.
Acceptance criteria:
It dissolves completely, and the solution is clear.
• Selenate and Sulfate
Sample solution:
Dissolve 0.5 g in 10 mL of water.
Analysis:
Add 0.1 mL of hydrochloric acid and 1 mL of barium chloride TS to the Sample solution, and mix.
Acceptance criteria:
No turbidity or precipitate is formed in 10 min.
ADDITIONAL REQUIREMENTS
• Packaging and Storage:
Preserve in tight containers.
Auxiliary Information
Please check for your question in the FAQs before contacting USP.
USP35NF30 Page 4623
Pharmacopeial Forum: Volume No. 29(5) Page 1571
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