Trisodium and tetrasodium edetate (EDTA)

Ethylenediaminetetraacetic acid (EDTA), also known by several other names, is a chemical used for both industrial and medical purposes.

It is an aminopolycarboxylic acid and a colourless, water-soluble solid. Its conjugate base is ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate (“six-toothed”) ligand and chelating agent, i.e., its ability to “sequester” metal ions such as Ca²⁺ and Fe³⁺. After being bound by EDTA into a metal complex, metal ions remain in solution but exhibit diminished reactivity. EDTA is produced as several salts, notably disodium EDTA and calcium disodium EDTA.