Specifications of Sodium Thiosulfate Anhydrous surpassing IP BP USP and Reagent Grade Standards:
Description: It appears as white powder free from foreign particles.
Solubility 10% aqueous solution: Freely soluble in water.
Identification:
(A)Reaction of Sodium
(B)Reaction of Thiosulphate
A solution responds to the test for Sodium and for Thiosulphate
Insoluble Matter: Not more than 0.25%
Calcium: Prescribed Test. No turbidity is produced.
pH: 6 to 8.4
Sulphites and Sulphates: Maximum 0.5%
Heavy Metals: Maximum 0.001%
Sodium Sulphite: Maximum 0.5%
Iron as Fe: Not more than 0.001%
Residual Solvent: To meet the requirement
Assay: Not less than 99% and not more than 100.5% of Na2S2O3 on anhydrous basis.

Specifications of Sodium Thiosulfate USP Grade
Na2S2O3-5H2O 248.19

Contains not less than 99.0 percent and not more than 100.5 percent of Na2S2O3, calculated on the anhydrous basis.

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 and for Thiosulfate.
Water: Dry about 1.0 g, accurately weighed, in vacuum at 40 o to 45o for 16 hours: it loses between 32.0% and 37.0% of its weight.
Calcium: Dissolve 1 g Sodium Thiosulfate in 20 mL of water, and add a few mL of ammonium oxalate: no turbidity is produced.
Heavy metals: the limit is 0.002%.

Specifications of Sodium Thiosulphate BP Ph Eur Grade
Na2S2O3-5H2O

DEFINITION
Content: 99.0 per cent to 101.0 per cent of Na2S2O3,5H2O.

CHARACTERS
Appearance: Transparent, colorless crystals, efflorescent in dry air.
Solubility: Very soluble in water, practically insoluble in ethanol 96 per cent. It dissolves in its water of crystallization at about 49°C.

IDENTIFICATION
A. It decolorizes iodinated potassium iodide solution.
B. To 0.5 ml of solution S (see Tests) add 0.5 ml of water R and 2 ml of silver nitrate solution. A white precipitate is formed which rapidly becomes yellowish and then black.
C. To 2.5 ml of solution S add 2.5 ml of water and 1 ml of hydrochloric acid. A precipitate of sulphur is formed and gas is evolved which gives a blue colour to starch iodate paper.
D. 1 ml of solution S gives reaction of sodium.

TESTS
Solution S: Dissolve 10.0 g in carbon dioxide-free water R prepared from distilled water R and dilute to 100 ml with the same solvent.
Appearance of solution: The freshly prepared solution is clear and colourless.
Dissolve 10.0 g in 50 ml of distilled water, add 1 ml of 0.1 M sodium hydroxide and dilute to 100 ml with the same solvent.
pH: 6.0 to 8.4 for the freshly prepared solution S.
Sulphates and sulphites: Maximum 0.2 per cent.
Sulphides: To 10 ml of solution S add 0.05 ml of a freshly prepared 50 g/l solution of sodium nitroprusside. The solution does not become violet.
Heavy metals: Maximum 10 ppm.