Description
SMBS is a widely used chemical compound with the full name Sodium Metabisulfite. It is also sometimes referred to as sodium pyrosulfate or disodium.
SMBS, or Sodium Metabisulfite, is a versatile chemical compound with a wide range of uses, primarily due to its properties as a strong reducing agent, antioxidant, and preservative.
Chemical Properties
| Hazard Class | Irritant; releases toxic SO₂ |
| Property | Details |
| Chemical Name | Sodium Metabisulfite |
| Chemical Formula | Na₂S₂O₅ |
| CAS Number | 7681-57-4 |
| Molecular Weight | 190.10 g/mol |
| Chemical Type | Inorganic sulfite salt |
| Appearance | White to pale yellow crystalline powder |
| Odor | Strong sulfur dioxide (SO₂) odor |
| pH (1% aqueous solution) | 3.5 – 5.0 |
| Solubility in Water | Freely soluble |
| Solubility in Organic Solvents | Insoluble |
| Decomposition | Decomposes in acids, releasing SO₂ gas |
| Reactivity | Strong reducing agent |
| Oxidation | Oxidizes in air to sodium sulfate |
| Hygroscopic Nature | Slightly hygroscopic |
| Stability | Stable under dry, cool conditions |
| Incompatible Materials | Acids, oxidizing agents |
| Hazard Class | Irritant; releases toxic SO₂ |
Uses
- Food and Beverage Industry
SMBS is a very common food additive (E223) used for its preservative and antioxidant qualities.
Preservative: It prevents the growth of microbes like bacteria, yeast, and mold, extending the shelf life of various foods. It’s particularly used for dried fruits, vegetables, and fruit juices.
Antioxidant: It prevents oxidative browning in produce, helping to maintain the color of foods like dried fruits and processed potatoes.
Winemaking and Brewing: SMBS is a critical ingredient in these processes. In winemaking, it’s used to sanitize equipment and to inhibit the growth of wild yeast and bacteria before fermentation begins. It also acts as an antioxidant to protect the wine’s flavor and color from oxidation.
Baking: It is used as a dough conditioner in some baked goods to help loosen the dough, making it easier to work with.
- Water Treatment
SMBS plays a crucial role in water treatment and purification systems.
Dechlorination: It’s widely used to remove excess chlorine and chloramines from water. This is essential for protecting sensitive equipment, such as reverse osmosis (RO) membranes, which can be damaged by chlorine.
Oxygen Scavenger: It is also used to remove dissolved oxygen from industrial water systems and boilers to prevent corrosion of metal pipes and tanks.
- Industrial Applications
SMBS is used in numerous industrial processes for its chemical properties.
Textile and Paper Industries: It acts as a bleaching and dechlorinating agent in the production of textiles and paper pulp.
Photography: It is a component of some photographic developing solutions, where it acts as an antioxidant to prevent the developer from oxidizing.
Gold Refining: SMBS is used to precipitate gold from a solution, such as an aqua regia solution, in the process of refining gold.
Leather Tanning: It is used in the leather industry to help in the tanning process.
- Pharmaceutical and Cosmetic Industry
In these fields, SMBS is used as an excipient—a pharmacologically inactive substance that helps with the formulation and stability of a product.
Antioxidant and Preservative: It’s included in some pharmaceutical formulations and cosmetics to prevent the oxidation of active ingredients and to extend the product’s shelf life. It’s found in some adrenaline (epinephrine) injections to prevent the drug’s degradation.
Medical Testing: In clinical settings, it can be used in a specific blood test to help identify sickle cell anemia.
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