Packaging and storage—
Preserve in tight containers.
Identification—
A:
To a solution (1 in 10) add a few drops of
iodine TS: the color is discharged.
B:
A solution (1 in 10) responds to the tests for
Sodium 
191
and for
Thiosulfate 191.
Water 921—
Dry about 1.0 g, accurately weighed, in vacuum at 40
to 45
for 16 hours: it loses between 32.0% and 37.0% of its weight.
Calcium—
Dissolve 1 g in 20 mL of water, and add a few mL of
ammonium oxalate TS: no turbidity is produced.
Heavy metals 231—
Dissolve 1 g in 10 mL of water, slowly add 5 mL of 3 N hydrochloric acid, evaporate on a steam bath nearly to dryness, and heat the residue at 150
for 1 hour. Add 15 mL of water to the residue, boil gently for 2 minutes, and filter. Heat the filtrate to boiling, and add sufficient bromine TS to produce a clear solution and provide a slight excess of bromine. Boil the solution to expel the excess bromine, cool to room temperature, add 1 drop of phenolphthalein TS, and neutralize with 1 N sodium hydroxide. Dilute with water to 25 mL: the limit is 0.002%.
Assay—
Dissolve about 800 mg of Sodium Thiosulfate, accurately weighed, in 30 mL of water. If necessary, adjust by the addition of 3 N hydrochloric acid to a pH of between 6.2 and 6.7 and titrate with 0.1 N iodine VS, adding 3 mL of
starch TS as the endpoint is approached. Each mL of 0.1 N iodine is equivalent to 15.81 mg of Na
2S
2O
3.
Auxiliary Information—
Staff Liaison :
Elena Gonikberg, Ph.D., Scientist
Expert Committee : (MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
USP29–NF24 Page 1993
Pharmacopeial Forum : Volume No. 29(5) Page 1579
Phone Number : 1-301-816-8251
