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Magnesium sulfate

Magnesium sulfate suppliers and sourcing guide

Magnesium sulfate occurs naturally as the mineral epsomite and is made by neutralizing magnesium oxide, hydroxide or carbonate with sulfuric acid and crystallizing the solution; some grades come from natural mineral deposits or brines. The heptahydrate, known as Epsom salt, is the common form, with dried and monohydrate grades carrying more magnesium per gram. Brands buy food or USP grade for supplements, brewing water adjustment and bath and cosmetic products.

See suppliersWhat to ask for on the COA
Also known as
MgSO4 · Epsom salt · Magnesium sulfate heptahydrate · E518
Facts checked
November 2026

Forms and grades of magnesium sulfate

Suppliers sell different products under the same name. Specify the one you need.

  • Heptahydrate (Epsom salt)

    Colorless crystals with seven waters of hydration and about 10% magnesium; used in food, brewing and bath products.

  • Monohydrate or dried

    Partly dehydrated grades with more magnesium per gram, used where bulk or water content matters.

  • Anhydrous

    Fully dried grade, very hygroscopic, used in some tablets and premixes.

  • Nonsynthetic grades

    Magnesium sulfate from natural mineral sources, specified where organic rules require nonsynthetic material.

  • Technical and agricultural grades

    Lower-purity grades sold for fertilizer and industry, which should not be used in food or supplements.

What to check on the COA

Compare each result with your own specification when the lot arrives.

Assay
Magnesium sulfate content on the ignited basis by EDTA titration, against a USP or Food Chemicals Codex specification.
Loss on ignition
Water of hydration, which confirms heptahydrate, monohydrate or dried grade.
Chloride and iron
Limit tests for common impurities from the raw material.
Lead, arsenic and selenium
Heavy metals and selenium by ICP-MS or compendial methods.
pH
pH of a solution, which flags free acid or alkali left from manufacture.

Storage, lots and expiry

Storage and shelf life

Keep magnesium sulfate in closed containers in a cool, dry area; the heptahydrate can lose water in warm, dry air and cake in humid air, and the dried grades absorb moisture quickly. Store food grade apart from technical grade to avoid mix-ups. Shelf life is set by the supplier's specification, with retest of assay and loss on ignition on aged stock.

Lots and expiry dates

Record the hydrate form, assay and loss on ignition for each lot, since magnesium per gram changes with hydration. For organic products, keep documentation that the lot is from a nonsynthetic source.

Regulatory status

Facts from regulators and standards bodies, each linked to its source.

This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.

Magnesium sulfate suppliers

Manufacturers and distributors whose own websites say they sell it.

We are checking magnesium sulfate suppliers now

Every listing is checked against the supplier’s own website before it goes live, so this list fills in over the coming weeks. The specs and COA checklist above are ready today.

Sell magnesium sulfate? Request a listing

Frequently asked questions

What forms of magnesium sulfate can brands buy?

Common forms include heptahydrate (Epsom salt), monohydrate or dried, anhydrous, nonsynthetic grades and technical and agricultural grades. Ask each supplier for the specification sheet of the exact grade they quote.

What should the COA for magnesium sulfate include?

Expect assay, loss on ignition, chloride and iron, lead, arsenic and selenium and pH, each with its method, specification and result for that lot.

How should magnesium sulfate be stored?

Keep magnesium sulfate in closed containers in a cool, dry area; the heptahydrate can lose water in warm, dry air and cake in humid air, and the dried grades absorb moisture quickly. Store food grade apart from technical grade to avoid mix-ups. Shelf life is set by the supplier's specification, with retest of assay and loss on ignition on aged stock.

What is the regulatory status of magnesium sulfate?

21 CFR 184.1443 affirms magnesium sulfate as GRAS for use as a flavor enhancer, nutrient supplement and processing aid at levels not to exceed current good manufacturing practice. 7 CFR 205.605(a) allows magnesium sulfate in or on processed products labeled organic from nonsynthetic sources only. Health Canada's Multi-Vitamin/Mineral Supplements monograph for natural health products lists magnesium sulfate and its hydrates among the source ingredients for magnesium (Table 2).

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