Thiosulfuric acid, disodium salt, pentahydrate.
Disodium thiosulfate pentahydrate. [10102-17-7].
Anhydrous. 158.11 [7772-98-7].
» Sodium Thiosulfate contains not less than 99.0 percent and not more than 100.5 percent of Na2S2O3, calculated on the anhydrous basis.
Packaging and storage Preserve in tight containers.
A: To a solution (1 in 10) add a few drops of iodine TS: the color is discharged.
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 Na2S2O3.
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USP32NF27 Page 3586Pharmacopeial Forum: Volume No. 29(5) Page 1579