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Selenious Acid
H2SeO3
128.97
Selenium dioxide,monohydrated. Selenious acid [7783-00-8]. »Selenious Acid contains not less than 93.0percent and not more than 101.0percent of H2SeO3.
Packaging and storage—
Preserve in tight containers.
Identification—
A:
Dissolve about 50mg in 5mLof water,add about 100mg of sodium bicarbonate,and mix:gas bubbles develop.
B:
Dissolve about 50mg in 5mLof 0.1Nhydrochloric acid,and add about 50mg of stannous chloride:a curdy tan-orange precipitate is formed.
Residue on ignition á281ñ:
not more than 1.0mg,from 10.0g (0.01%).
Insoluble matter—
Dissolve 1g in 5mLof water:it dissolves completely and the solution is clear.
Selenate and sulfate—
Dissolve about 0.5g in 10mLof water,add 0.1mLof hydrochloric acid and 1mLof barium chloride TS,and mix:no turbidity or precipitate is formed in 10minutes.
Organic volatile impurities,Method Iá467ñ:
meets the requirements.
Assay—
Transfer about 100mg of Selenious Acid,accurately weighed,to a suitable glass-stoppered flask,and dissolve in 50mLof water.Add 10mLof potassium iodide solution (3in 10)and 5mLof hydrochloric acid,mix,insert the stopper in the flask,and allow to stand for 10minutes.Add 50mLof water and 3mLof starch TS,and titrate with 0.1Nsodium thiosulfate VSuntil the solution is colorless,then titrate with 0.1Niodine VSto a blue endpoint.Subtract the volume of 0.1Niodine from the volume of 0.1Nsodium thiosulfate to obtain the volume of 0.1Nsodium thiosulfate equivalent to selenious acid.Each mLof 0.1Nsodium thiosulfate is equivalent to 3.225mg of H2SeO3.
Auxiliary Information—
Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1763
Pharmacopeial Forum:Volume No.29(5)Page 1571
Phone Number:1-301-816-8251
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