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What it is. EDTA disodium salt dihydrate (disodium ethylenediaminetetraacetate dihydrate, CAS 6381-92-6) is a white crystalline powder and the most widely used solid form of EDTA in the lab. This ACS grade material is supplied in a 1 lb size for preparing volumetric titrants, buffers, and chelating solutions.
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What ACS grade guarantees. ACS reagent disodium EDTA dihydrate assays at 99.0 to 101.0%, with limits of 0.005% insoluble matter, 0.005% heavy metals (as Pb), 0.01% iron, and 0.1% nitrilotriacetic acid, and a pH of 4.0 to 6.0 for a 5% solution at 25 °C. Those limits make it suitable as the starting material for standard EDTA titrants.
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Chemical identity. The dihydrate has the formula C10H14N2Na2O8·2H2O and a molecular weight of 372.24 g/mol. Two of EDTA's four carboxylic acid groups carry sodium, which makes the salt far more water-soluble than EDTA free acid while keeping solutions mildly acidic.
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How EDTA chelates metals. EDTA is a hexadentate ligand: two nitrogen atoms and four carboxylate groups wrap around a metal ion and bind it in a stable, water-soluble one-to-one complex. That strong, predictable binding underlies EDTA titrations, metal sequestration in buffers, and scale removal.
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Preparing EDTA titrants. To make a 0.1 M titrant, dissolve 37.22 g of the dihydrate in deionized water and dilute to 1 L; for 0.01 M, use 3.722 g per liter (calculated). Many labs dry the salt before weighing and standardize the finished solution against calcium carbonate or zinc. For a ready-made option, see Lab Pro's EDTA Disodium Solution, 0.1 M (0.2 N).
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Water hardness and metal analysis. Disodium EDTA is the titrant of choice for total hardness, calcium, and magnesium in water, using Eriochrome Black T in an ammonia buffer near pH 10. It also assays zinc, nickel, copper, and other metals in plating baths and process streams.
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Biochemistry and molecular biology. In biochemistry, researchers add disodium EDTA to buffers such as TE and lysis buffers to bind magnesium and calcium, inactivating metal-dependent nucleases and proteases and protecting DNA and proteins during handling.
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Industrial and cleaning uses. Beyond the lab, EDTA salts soften water, prevent scale in boilers and cleaning formulations, and stabilize products against metal-catalyzed degradation. The ACS grade suits analytical work where trace impurity control matters.
Technical Specifications
| Chemical Name |
Ethylenediaminetetraacetic acid disodium salt dihydrate |
| CAS Number |
6381-92-6 |
| Alternate CAS (anhydrous disodium salt) |
139-33-3 |
| EC Number |
205-358-3 |
| Synonyms |
Disodium EDTA, EDTA-Na2, edetate disodium, disodium dihydrogen ethylenediaminetetraacetate |
| Formula |
C10H14N2Na2O8·2H2O |
| Molecular Weight |
372.24 g/mol |
| Grade |
ACS reagent |
| Assay |
99.0 to 101.0% |
| pH (5% solution, 25 °C) |
4.0 to 6.0 |
| Insoluble Matter |
0.005% max |
| Heavy Metals (as Pb) |
0.005% max |
| Iron (Fe) |
0.01% max |
| Nitrilotriacetic Acid |
0.1% max |
| Appearance |
White crystalline powder |
| Melting Point |
About 255 °C (decomposes) |
| Binding Ratio |
1:1 EDTA to metal ion |
| Grams per Liter for 0.1 M |
37.22 g (calculated) |
| Package Size |
1 lb |
Applications / Common Uses
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EDTA titrant preparation: Dissolves to make standard 0.1 M, 0.05 M, and 0.01 M titrants.
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Water hardness testing: Titrates calcium and magnesium with Eriochrome Black T.
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Metal assays: Determines zinc, nickel, copper, and other metals.
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Molecular biology buffers: Chelates magnesium and calcium in TE and lysis buffers.
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Scale and metal control: Sequesters metal ions in cleaning and process solutions.
Storage, Handling & Shipping
Store tightly closed in a cool, dry place at room temperature. The dihydrate is stable under normal conditions, but keep it away from strong oxidizers and moisture, and avoid generating dust when weighing.
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Incompatible materials: Strong oxidizers and strong bases.
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Personal protection: Safety glasses, nitrile gloves, and dust control when weighing.
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Spill response: Sweep up without raising dust and place in a closed container for disposal.
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First aid: Eyes: rinse with water for several minutes. Inhalation: move to fresh air.
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