Sodium thiosulfate

Sodium thiosulfate (CAS 7772-98-7), also sold as sodium thiosulphate and approved as E539, is an inorganic salt used industrially as a reducing and dechlorinating agent.

Where is Sodium thiosulfate used?

• Water treatment: dechlorination of municipal and industrial effluent, a standard step where residual chlorine would interfere with biological treatment
• Textile and paper: neutralising chlorine bleach after whitening to prevent fibre or pulp degradation
• Pharmaceutical manufacturing: antioxidant stabiliser in injectable formulations and active ingredient in antidote preparations for cyanide and heavy metal exposure
• Photographic and printing: fixing agent that clears unexposed silver halides, still relevant in specialty analog processes
• It neutralises excess oxidants in process streams and protects sensitive materials from chlorine damage.
• Forms soluble complexes with certain heavy metals to facilitate their removal from industrial waste effluents.
• Used as a topical antifungal agent, possibly in combination with salicylic acid, for tinea versicolor (pityriasis versicolor) and other fungal skin infections.
• Converts dyes into their soluble colorless forms called leuco.
• Used in gold mining, water treatment, analytical chemistry, silver-based photographic film and print development, and medicine.

Formulation notes

• Reacts violently with strong oxidants.
• For photographic fixing, ammonium thiosulfate is generally preferred over sodium thiosulfate.
• For photographic and general use, the pentahydrate form is recommended.

Typical specification

• Content is specified as 29.0–31.0 wt% as Na2S2O3.
• Usually found as white or colorless pentahydrate, Na2S2O3·5H2O.
• Available in photographic grade, food grade and industrial grade.

Regulatory status

• Has the ATC code V03AB06 and is classified as an antidote.
• Registered under the REACH Regulation and is manufactured and/or imported in the European Economic Area at ≥ 1,000 to < 10,000 tonnes per year.
• In the European Union, sodium thiosulfate (Pedmarqsi) is indicated for the prevention of ototoxicity induced by cisplatin chemotherapy in patients 1 month to < 18 years of age with localized, non-metastatic, solid tumors.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.