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Ethylenediaminetetraacetic acid description

Release date:2016-11-1 11:57:54 Browsing times:1363

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EDTA is a widely used acronym for the chemical compound ethylenediaminetetraacetic acid. EDTA is a polyamino carboxylic acid with the formula [CH2N(CH2CO2H)2]2. This colourless, water-soluble solid is widely used to dissolve scale. Its usefulness arises because of its role as a 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


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 similar manner, EDTA is added to some food as a preservative or stabilizer to prevent catalytic oxidative decolouration, which is catalyzed by metal ions. In personal care products, it is added to cosmetics to improve their stability toward air. In Soft drinks containing ascorbic acid and sodium benzoate, EDTA mitigates formation of benzene (a carcinogen).


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+ and Mg2+ ions 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 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, iron forms insoluble salts, which are less bioavailable, at near-neutral pH. 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.


EDTA was an most important chelating agents 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 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.


Medicine


EDTA is used to bind metal ions in chelation therapy, e.g., for mercury and lead poisoning. It is used in a similar manner to remove excess iron from the body. This therapy is used to treat the complication of repeated blood transfusions, as would be applied to treat thalassaemia. EDTA acts as a powerful antioxidant to prevent free radicals from injuring blood vessel walls.


Dentists use EDTA solutions to remove inorganic debris and prepare root canals for obturation. It serves as a preservative (usually to enhance the action of another preservative such as benzalkonium chloride or thiomersal) in ocular preparations and eyedrops. In evaluating kidney function, the complex [Cr(edta)]- is administered intravenously and its filtration into the urine is monitored. This method is useful for evaluating glomerular filtration rate.


EDTA is used extensively in the analysis of blood. It is an anticoagulant for blood samples for CBC/FBEs (complete blood count also known as full blood examination).


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