EDTA

chemical structure of EDTA - ethylene-diamine-tetraacetic acid

EDTA (black) with coordinate bonds to a metal ion (red)

EDTA stands for ethylene-diamine-tetraacetic acid. It chelates divalent cations and is therefore used in many buffers. Its relative EGTA has a higher affinity for calcium than EDTA.

Purpose

• EDTA is a synthetic amino acid and chelating agent for divalent metals.

• Most enzymes that synthesize or modify nucleic acids (e.g. polymerases, ligases, kinases, nucleases) are Mg²⁺-dependent. The addition of EDTA is a convenient way to stop these reactions.

• EDTA is a component of many buffers used to store DNA, such as TE buffer, where the EDTA removes the metal cofactors (typically Mg⁺⁺ required for activity of DNAses and other DNA damaging enzymes.

Procurement

• Usually sold as the disodium salt (CAS 6381-92-6) (Sigma E1644).

Use

• Molecular Weight, disodium salt dihydrate: 372.24

• EDTA is essentially insoluble in water, and will only dissolve when neutralized with sodium hydroxide to a pH = 8.0

• Standard stock solutions are 0.5M at pH 8.0. A 1M solution cannot be made. Autoclave.

• Making the standard solution from disodium EDTA (the typical form sold) requires approximately 1 molar equivalent of NaOH

• pK₁ = 1.99
• pK₂ = 2.67
• pK₃ = 6.16
• pK₄ = 10.26

EDTA stock solution recipes

0.5 M EDTA stock

• 16.81 g EDTA (Sodium Salt)
• dH2O to 90 ml
• adjust pH to 7.0
• adjust volume to 100 ml

0.5M 500ml pH 8.0 with NaOH pre-calculated

• 93.05g of Na2.EDTA (FW 372.2)
• 10.14g of NaOH (FW 40)
• 500 ml dH2O

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Storage and stability

• store at room temperature
• stable for years

Interesting facts

• Here's an article that speaks of the wonders of EDTA and how it can help treat Aunt Edna's cardiovascular disease, enhance your enjoyment of the Friday night happy hour, and act as a "get out of jail free" card.

• EDTA can prolong the life of your motorcycle battery!

• EDTA helps you determine the hidden contents of your hard water.

Safety

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References

• Here's a great page about EDTA, including formation constant (K_f) values for metal-EDTA complexes. Note that many heavy metal ions (like Fe³⁺, Co²⁺, and Zn²⁺) are chelated much more strongly than Mg²⁺. A little bit of EDTA in your reaction will go a long way to keep these evildoers out of trouble and away from your precious biomolecules without interfering with your Mg²⁺-dependent reactions.