Product description :

Ethylenediaminetetraacetic acid
Ethylenediaminetetraacetic acid, widely abbreviated as EDTA (for other names, see Table), is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named 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, metal ions remain in solution but exhibit diminished reactivity. EDTA is produced as several salts, notably disodium EDTA and calcium disodium EDTA.

Uses

[edit] Industry

In industry, EDTA is mainly used to sequester metal ions in aqueous solution. In the textile industry, it prevents metal ion impurities from modifying colours of dyed products. In the pulp and paper industry, EDTA inhibits the ability of metal ions, especially Mn²⁺, from catalyzing the disproportionation of hydrogen peroxide, which is used in "chlorine-free bleaching." In a similar manner, EDTA is added to some food as a preservative or stabilizer to prevent catalytic oxidative decoloration, which is catalyzed by metal ions.^[8] In personal care products, it is added to cosmetics to improve their stability toward air.^[9] In soft drinks containing ascorbic acid and sodium benzoate, EDTA mitigates formation of benzene (a carcinogen).^[10]

The reduction of water hardness in laundry applications and the dissolution of scale in boilers both rely on EDTA and related complexants to bind Ca²⁺, Mg²⁺, as well as other metal ions. Once bound to EDTA, these metal centers tend not to form precipitates or to interfere with the action of the soaps and detergents. For similar reasons, cleaning solutions often contain EDTA.

The solubilization of ferric ions near neutral pH is accomplished using EDTA. This property is useful in agriculture including hydroponics, especially in calcareous soils. Otherwise, at near-neutral pH, iron(III) forms insoluble salts, which are less bioavailable. Aqueous [Fe(edta)]^- is used for removing ("scrubbing") hydrogen sulfide from gas streams. This conversion is achieved by oxidizing the hydrogen sulfur to elemental sulfur, which is non-volatile:

2 [Fe(edta)]^- + H₂S → 2 [Fe(edta)]²⁻ + S + 2 H⁺

In this application, the ferric center is reduced to its ferrous derivative, which can then be reoxidized by air. In similar manner, nitrogen oxides are removed from gas streams using [Fe(edta)]^2-. The oxidizing properties of [Fe(edta)]^- are also exploited in photography, where it is used to solubilize silver particles.^[4]

EDTA was used in the separation of the lanthanide metals by ion-exchange chromatography. Perfected by F.H. Spedding et al. in 1954, the method relies on the steady increase in stability constant of the lanthanide EDTA complexes with atomic number. Using sulfonated polystyrene beads and copper(II) as a retaining ion, EDTA causes the lanthanides to migrate down the column of resin while separating into bands of pure lanthanide. The lanthanides elute in order of decreasing atomic number. Due to the expense of this method, relative to counter-current solvent extraction, ion-exchange is now used only to obtain the highest purities of lanthanide (typically greater than 4N, 99.99%).^{[citation needed]}