Sodium metabisulfite or sodium pyrosulfite is an inorganic compound of the chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent.

Uses of Sodium Metabisulfite:

• Sodium and potassium metabisulfite have many major and niche uses. It is widely used for preserving food and beverages.
• In combination with sodium hydrosulfite, it is used as a rust-stain remover.
• It is used in photography.
• Concentrated sodium metabisulfite can be used to remove tree stumps. Some brands contain 98% sodium metabisulfite and cause degradation of lignin in the stumps, facilitating removal.
• It is also used as an excipient in some tablets, such as paracetamol.

• A very important health-related aspect of this substance is that it can be added to a blood smear in a test for sickle cell anemia (and other similar forms of hemoglobin mutation). The substance causes defunct cells to sickle (through a complex polymerization), hence confirming the disease.
• It is used as a bleaching agent in the production of coconut cream.
• It (or liquid SO2) is commonly used as an antimicrobial and antioxidant in winemaking; bottled wine indicates its use with the label “Contains Sulfites” in the US.
• It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibers, thus allowing the garment to go back to its original shape after washing.
• It is used as an SO2 source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes.
• It is used as an SO2 source (mixed with air or oxygen) for the precipitation of elemental gold in chloroauric (aqua regia) solutions.
• It is used in the water treatment industry to quench residual chlorine.
• It is used in tint etching of iron-based metal samples for microstructural analysis.
• It is used as a fungicide for anti-microbial and mold prevention during the shipping of consumer goods such as shoes and clothing. Plastic stickers and packaging (such as Micro-Pak™) containing the anhydrous sodium metabisulfite solid active ingredient are added before shipping. The devices absorb moisture from the atmosphere during shipping and release low levels of sulfur dioxide.
• It is used for preserving fruit during shipping.
• It is used as a solvent in the extraction of starch from tubers, fruit, and cereal crops.
• It is used as a pickling agent to treat high-pressure reverse osmosis water desalination membranes for extended storage periods between uses.