Ethylenediaminetetraacetic Acid (EDTA)

  • EDTA is a polyaminocarboxylic acid. Its conjugate base is  ethylenediaminetetraacetate.
  • It is a colorless compound that was first synthesized by Ferdinand Mün in 1935.
  • EDTA is best known for its chelating property. It sequesters metal ions such as Ca2+ and Fe3+. (Read more: ).
  • EDTA forms coordination complexes with metal ions. It has 6 lone pairs of electrons (two nitrogen atoms and four oxygen atoms) which can participate in formation of coordinate bonding with metal ions (hexadendate ligand).
EDTA structure
EDTA structure
  • Most applications of EDTA rely on its ability to chelate metal ions. Metal ions bound to EDTA remain in solution but unable to participate in reactions and show no activity. 
  • Since metal ions are necessary for many enzymatic reactions, the presence of EDTA stops the activity of these enzymes. This is the reason why DNA is stored in an EDTA-containing solution. 
  • EDTA is commercially available as _ _ _ _ _
    • Anhydrous EDTA (CAS Number 60-00-4, Molecular Weight 292.24)
    • Disodium EDTA dihydrate (EDTA.Na2.2H2O, CAS Number 6381-92-6, Molecular Weight 372.24) and
    • Tetrasodium EDTA tetrahydrate (EDTA.Na4.4H2O, CAS Number 13235-36-4, Molecular Weight 452.23).
  • Anhydrous free acid EDTA is least soluble among all EDTA forms in water. To dissolve anhydrous free acid EDTA in water, a lot of NaOH (3.1 ratios) is added to bring the pH to 8.0.
  • Disodium EDTA dihydrate has better solubility than anhydrous free acid EDTA and is most commonly used for the preparation of a 0.5 M EDTA solution.
  • Tetrasodium EDTA tetrahydrate is soluble in water. The resulting solution has a pH above 10.0, therefore is not suitable for cell and molecular biology experiments.
  • In molecular biology laboratories, EDTA is used for the preparation of many solutions including TAE, TBE, DNA loading dye, resuspension buffer (isolation of plasmid), Tris-EDTA, etc.
  • Since divalent metal ions also strengthen cell-cell and cell-substratum interaction, EDTA is also added in commonly used cell dissociation reagents such as Trypsin-EDTA solution. 
  • It has been widely used in domestic products like food preservatives and cosmetic stabilizers. It is also used extensively to dissolve limescale. Our daily use products like personal care, skin care, processed foods, cosmetic preparations, and cleaning products often contain EDTA. It has extensive medical, engineering, agricultural, and industrial applications as well.
  • EDTA applications in medical science (chelation therapy)
    • Eye drops containing EDTA are used to treat calcium deposits in the eye.
    • EDTA is sometimes used as an ointment for skin irritations produced by metals such as chromium, nickel, and copper.
    • EDTA is also used to treat lead poisoning or heavy metal toxicity.

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