Sodium metabisulfite

Sodium metabisulfite (CAS 7681-57-4), also known as sodium pyrosulfite and sold under the abbreviation SMBS, is an inorganic sulfite salt. As E223, it is a regulated food additive recognized in major international markets.

Where is Sodium metabisulfite used?

• Food and beverage: preservative, antioxidant and reducing agent that prevents oxidative browning and microbial spoilage in dried fruits, wines, seafood and fruit juices
• Water treatment: neutralizes residual chlorine in municipal and industrial effluent streams
• Textile and leather: bleaching and reducing agent in dye stripping and chrome tanning
• Pharmaceutical manufacturing: antioxidant stabilizer in injectable formulations and oral solutions
• It releases sulfur dioxide under controlled conditions.
• Cleaning of equipment by neutralizing chlorine or ozone residues.
• Reduction of mixing time requirements of flours.

Formulation notes

• Dosage in water treatment is calculated based on chlorine concentration, flow rate, and contact time; low dose leaves chlorine residue, while overdose can lower dissolved oxygen too much.

Typical specification

• Food grade E223 has a maximum iron content of 5 ppm.
• Decomposes at 150°C.
• Assay (Na2S2O5) specification is 98.0-100.0% with typical 98.6%.

Regulatory status

• Occupational exposure limit (TLV) is 5 mg/m³ as TWA, classified as A4 (not classifiable as human carcinogen).

Storage, packaging and handling

• Strong reducing agent; reacts violently with oxidants, creating a fire hazard.
• Store separately from acids, strong oxidants, and food and feed substances.
• Should be stored in a cool, dry, well-ventilated area away from moisture and acids; packaging must be kept closed and not come into direct contact with water.

Frequently asked questions about Sodium metabisulfite

What is the UN classification and packing group for sodium metabisulfite?

This product is not regulated for transport under UN regulations.

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