Sodium metabisulfite

Chemical properties

Sodium metabisulfite is a white crystalline powder with a sulfur dioxide odor and can be regarded as the anhydride of two molecules of sodium disulfite.

The Uses of Sodium metabisulfite

Sodium metabisulfite is a preservative and antioxidant that exists as crystals or a powder with a sulfur dioxide odor, and is readily soluble in water. It is used in dried fruits to preserve flavor and color while inhibiting microbial growth, prevents oxidative "black spots" in shrimp, and serves as a preservative in maraschino cherries and lemon drinks. For further details, see sulfur dioxide.

What are the applications of Application

Sodium metabisulfite is an antioxidant reducing agent, with antimicrobial and antifungal properties

Production Methods

Sodium metabisulfite is prepared by saturating a solution of sodium hydroxide with sulfur dioxide and allowing crystallization to occur; hydrogen is passed through the solution to exclude air. Sodium metabisulfite may also be prepared by saturating a solution of sodium carbonate with sulfur dioxide and allowing crystallization to occur, or by thermally dehydrating sodium bisulfite.

General Description

Sodium metabisulfite (MBS, also known as sodium disulfite) is an inorganic salt and the sodium salt of disulfurous acid. It is widely used in textile dyeing, photography, and the paper industry, and is commonly added as a preservative to various food products and wines.

Health Hazard

Sodium metabisulfite may cause bronchospasm, oculonasal symptoms, and urticaria in sulfite-sensitive individuals; irritation of mucous membranes may occur from inhalation of the dust.

Flammability and Explosibility

Non flammable

Pharmaceutical Applications

Sodium metabisulfite is used as an antioxidant in oral, parenteral, and topical pharmaceutical formulations at concentrations of 0.01–1.0% w/v, and approximately 27% w/v in intramuscular injections. It is primarily employed in acidic preparations, with sodium sulfite preferred for alkaline systems. Exhibiting antimicrobial activity that is most effective at acid pH, it also serves as a preservative in oral preparations such as syrups. In the food and wine industries, it functions as an antioxidant, antimicrobial preservative, and antibrowning agent, though concentrations above approximately 550 ppm impart a noticeable flavor. Commercial sodium metabisulfite typically contains small amounts of sodium sulfite and sodium sulfate.

Contact allergens

This agent is frequently used as a preservative in pharmaceutical products, in the bread-making industry as an antioxidant, and it can induce contact dermatitis. It can be used as a reducing agent in photography and caused dermatitis in a photographic technician, probably acting as an aggravating irritative factor. Sodium metabisulfite contains a certain amount of sodium sulfite and sodium sulfate.

Safety Profile

An inhalation hazard. Poison by intravenous route. Moderately toxic by parenteral route. Experimental reproductive effects. Mutation data reported. When heated to decomposition it emits toxic fumes of SOx and Na2O.

Carcinogenicity

Sodium metabisulfite was genotoxic in mice in vivo as determined by chromosomal aberration, micronucleus, and sperm shape assays. It was not mutagenic in bacterial assays.

Storage

On exposure to air and moisture, sodium metabisulfite is slowly oxidized to sodium sulfate with disintegration of the crystals. Addition of strong acids to the solid liberates sulfur dioxide.
In water, sodium metabisulfite is immediately converted to sodium (Na+) and bisulfite (HSO3-) ions. Aqueous sodium metabisulfite solutions also decompose in air, especially on heating. Solutions that are to be sterilized by autoclaving should be filled into containers in which the air has been replaced with an inert gas, such as nitrogen. The addition of dextrose to aqueous sodium metabisulfite solutions results in a decrease in the stability of the metabisulfite.
The bulk material should be stored in a well-closed container, protected from light, in a cool, dry place.

Incompatibilities

A strong reducing agent. Keep away from oxidizers. Mixtures with water forms a strong corrosive. Contact with acids releases toxic fumes. Heat causes decomposition. Slowly oxidized to the sulfate on exposure to air and moisture. Attacks metals

Regulatory Status

GRAS listed. Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (epidural;inhalation; IM and IV injections; ophthalmic solutions; oral preparations; rectal, topical, and vaginal preparations). Included in nonparenteral and parenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.