Sodium Thiosulfate

Sodium Thiosulphate

(Ph. Eur. monograph 0414)

Na₂S₂O₃,5H₂O    248.2    10102-17-7

Used in treatment of cyanide poisoning.

Sodium Thiosulfate Injection

Ph Eur

99.0 per cent to 101.0 per cent of Na₂S₂O₃,5H₂O.

Transparent, colourless crystals, efflorescent in dry air.

Very soluble in water, practically insoluble in ethanol 96 per cent. It dissolves in its water of crystallisation at about 49 °C.

A. It decolourises iodinated potassium iodide solution R.

B. To 0.5 mL of solution S (see Tests) add 0.5 mL of water R and 2 mL of silver nitrate solution R2. 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 R and 1 mL of hydrochloric acid R. A precipitate of sulfur is formed and gas is evolved which gives a blue colour to starch iodate paper R.

D. 1 mL of solution S gives reaction (a) of sodium (2.3.1).

Dissolve 10.0 g in carbon dioxide-free water R prepared from distilled water R and dilute to 100 mL with the same solvent.

The freshly prepared solution is clear (2.2.1) and colourless (2.2.2, Method II).

Dissolve 10.0 g in 50 mL of distilled water R, add 1 mL of 0.1 M sodium hydroxide and dilute to 100 mL with the same solvent.

6.0 to 8.4 for the freshly prepared solution S.

Maximum 0.2 per cent.

Dilute 2.5 mL of freshly prepared solution S to 10 mL with distilled water R. To 3 mL of this solution first add 2 mL of iodinated potassium iodide solution R and continue the addition dropwise until a very faint persistent yellow colour appears. Dilute to 15 mL with distilled water R.

To 10 mL of solution S add 0.05 mL of a freshly prepared 50 g/L solution of sodium nitroprusside R. The solution does not become violet.

Maximum 10 ppm.

To 10 mL of solution S add 0.05 mL of sodium sulfide solution R. After 2 min, any brown colour in the solution is not more intense than that in a reference solution prepared at the same time and in the same manner using 10 mL of lead standard solution (1 ppm Pb) R.

Dissolve 0.500 g in 20 mL of water R and titrate with 0.05 M iodine, using 1 mL of starch solution R, added towards the end of the titration, as indicator.

1 mL of 0.05 M iodine is equivalent to 24.82 mg of Na₂S₂O₃,5H₂O.

In an airtight container.

Ph Eur