Sodium Metabisulfite

Sodium Metabisulfite is an inorganic white crystalline powder known for its sulfurous odour and multifunctional properties. It is extensively utilised in food preservation, pharmaceuticals, water treatment, and various industrial processes. This guide provides a detailed overview of Sodium Metabisulfite’s chemical and physical characteristics, key benefits, applications, safety protocols, and environmental considerations.

Chemicals Characteristics

Synonyms: Sodium pyrosulfite, disodium metabisulfite, sodium disulfite, E223
Chemical Formula: Na₂S₂O₅
CAS Number: 7681-57-4

Molar Weight

190.11 g/mol

Melting Point

170 °C

Boiling Point

Decomposes, liberating SO₂ gas

Flash Point

°C

Density

1.48 g/cc

Forms

White crystalline powder or granules

Entire form

Key Points/Overview

Sodium Metabisulfite is renowned for its antioxidant, reducing, and antimicrobial properties. It functions as a sulfur dioxide (SO₂) source, which helps extend the shelf life of food products, stabilise pharmaceuticals, and neutralise oxidising agents in industrial applications. Its capacity to decompose into sodium sulfite and SO₂ under heat or acidic conditions makes it highly versatile for a variety of chemical and preservation processes.

In addition to these functions, Sodium Metabisulfite’s role in preventing microbial growth and oxidation has made it an indispensable ingredient across multiple industries, including food technology, pharmaceuticals, and water treatment.

Uses & Benefits

Sodium Metabisulfite delivers substantial advantages across the food, pharmaceutical, and industrial sectors.

Food Industry

  • Preservative: Extends the shelf life of dried fruits, wines, and beverages by inhibiting microbial growth and oxidation. Its antioxidant action prevents spoilage and maintains product quality over time.

  • Bleaching Agent: Used to maintain colour and appearance in processed foods such as potatoes and shrimp, preserving their aesthetic and sensory qualities.

Pharmaceuticals

  • Antioxidant: Stabilises oxygen-sensitive medications and injectable formulations, prolonging their efficacy and safety.

  • Antifungal Agent: Inhibits microbial growth in topical pharmaceutical preparations, reducing the risk of contamination.

Industrial Applications

  • Leather Tanning: Acts as a reducing agent in chrome tanning, improving the texture and durability of leather products.

  • Water Treatment: Dechlorinates water and neutralises oxidising agents, ensuring water safety and quality.

  • Photography: Serves as a fixing agent in film development, contributing to image stability and clarity.

Safety Information

Potential Hazards

  • Skin and Eye Irritation: Can cause redness, itching, and burns upon contact. Protective gloves and goggles are essential.

  • Inhalation: Dust or SO₂ gas inhalation may result in coughing, shortness of breath, or pulmonary oedema.

  • Ingestion: Toxic if ingested in large quantities. Symptoms include nausea, vomiting, or metabolic acidosis.

Safety Precautions

  • Personal Protective Equipment (PPE): Nitrile gloves, safety goggles, and respiratory protection (N95 respirators) should be used.

  • Ventilation: Use in well-ventilated areas or employ local exhaust systems.

  • Emergency Response: In case of contact, rinse affected areas with water. For inhalation or ingestion, seek immediate medical attention.

Storage Recommendations

  • Containers: Store in tightly sealed containers resistant to corrosion.

  • Conditions: Keep in a cool, dry area away from acids and moisture.

Occupational Exposure Controls

  • Engineering Controls: Implement local exhaust ventilation and dust control measures.

  • Administrative Controls: Provide worker training on safe handling and emergency response.

  • Health Surveillance: Monitor employees for signs of respiratory or dermatological sensitivity.

Environmental Impact and Disposal

  • Environmental Considerations: Sulfite compounds can impact aquatic environments. Avoid uncontrolled release.

  • Disposal Guidelines: Dispose of in compliance with local hazardous waste regulations. Prevent discharge into water systems.

Sodium Metabisulfite’s multifunctional nature, combined with effective safety and environmental management, makes it a valuable compound in food preservation, pharmaceutical stabilisation, and industrial processing.