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Ethylenediaminetetraacetic acid (EDTA) is an
aminopolycarboxylic acid left, 120px, a metal complex with the EDTA anion 120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands. An aminopolycarboxylic acid (sometimes abbreviated APCA) is a chemical compound containing one or more nitrogen at ...
with the formula H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-soluble complexes even at neutral pH. It is thus used to dissolve Fe- and Ca-containing scale as well as to deliver iron ions under conditions where its oxides are insoluble. EDTA is available as several salts, notably disodium EDTA, sodium calcium edetate, and tetrasodium EDTA, but these all function similarly.


Uses


Textile industry

In industry, EDTA is mainly used to
sequester Sequestration or sequester may refer to: Law and government * Sequestration (law), the seizure of property for creditors or the state. See also Committee for Compounding with Delinquents * Jury sequestration, the isolation of a jury * Bankruptcy, ...
(bind or confine) metal ions in aqueous solution. In the
textile industry The textile industry is primarily concerned with the design, production and distribution of yarn, cloth and clothing. The raw material may be natural, or synthetic using products of the chemical industry. Industry process Cotton manufacturi ...
, 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 catalysing the
disproportionation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
of
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
, which is used in chlorine-free bleaching. In a similar manner, EDTA is added to some food as a
preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
or stabiliser to prevent catalytic oxidative decolouration, which is catalysed by metal ions.In soft drinks containing ascorbic acid and
sodium benzoate Sodium benzoate is the sodium salt of benzoic acid, widely used as a food preservative (with an E number of E211) and a pickling agent. It appears as a white crystalline chemical with the formula C6H5COONa. Production Sodium benzoate is commo ...
, EDTA mitigates formation of
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
(a
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...
).


Water softener

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 complexes are less likely to form precipitates or to interfere with the action of the
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s and detergents. For similar reasons, cleaning solutions often contain EDTA. In a similar manner EDTA is used in the cement industry for the determination of free
lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...
and free magnesia in cement and clinkers. The solubilisation of Fe3+ ions at or below near neutral pH can be accomplished using EDTA. This property is useful in
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...
including hydroponics. However, given the pH dependence of ligand formation, EDTA is not helpful for improving iron solubility in above neutral soils. Otherwise, at near-neutral pH and above, iron(III) forms insoluble salts, which are less
bioavailable In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
to susceptible plant species.


Scrubbing

Aqueous
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>− is used for removing (" scrubbing") hydrogen sulfide from gas streams. This conversion is achieved by oxidising the hydrogen sulfide to elemental sulfur, which is non-volatile: :2 
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>− + H2S → 2 
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>2− + S + 2 H+ In this application, the iron(III) centre is reduced to its iron(II) derivative, which can then be reoxidised by air. In similar manner, nitrogen oxides are removed from gas streams using
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>2−. The oxidising properties of
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>− are also exploited in
photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employe ...
, where it is used to solubilise
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
particles.


Ion-exchange chromatography

EDTA was used in separation of the
lanthanide metal The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
s by
ion-exchange chromatography Ion chromatography (or ion-exchange chromatography) separates ions and polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including large proteins, small nucleotides, and amino a ...
. 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 The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
. Using
sulfonate In organosulfur chemistry, a sulfonate is a salt or ester of a sulfonic acid. It contains the functional group , where R is an organic group. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-o ...
d polystyrene beads and Cu2+ as a retaining ion, EDTA causes the lanthanides to migrate down the column of resin while separating into bands of pure lanthanides. The lanthanides elute in order of decreasing atomic number. Due to the expense of this method, relative to
countercurrent solvent extraction Countercurrent may refer to: *Countercurrent pool *Countercurrent exchange *Countercurrent chromatography *Equatorial Counter Current *''Counter-Currents'', an alt-right online publication *''Countercurrents.org'', an Indian news website *two polit ...
, ion exchange is now used only to obtain the highest purities of lanthanides (typically greater than 99.99%).


Medicine

Sodium calcium edetate, an EDTA derivative, is used to bind metal ions in the practice of
chelation therapy Chelation therapy is a medical procedure that involves the administration of chelating agents to remove heavy metals from the body. Chelation therapy has a long history of use in clinical toxicology and remains in use for some very specific me ...
, such as for treating mercury and lead poisoning. It is used in a similar manner to remove excess
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
from the body. This therapy is used to treat the complication of repeated
blood transfusion Blood transfusion is the process of transferring blood products into a person's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but mo ...
s, as would be applied to treat
thalassaemia Thalassemias are inherited blood disorders characterized by decreased hemoglobin production. Symptoms depend on the type and can vary from none to severe. Often there is mild to severe anemia (low red blood cells or hemoglobin). Anemia can result ...
.


Dentistry

Dentists and
endodontist Endodontics (from the Greek roots ''endo-'' "inside" and ''odont-'' "tooth") is the dental specialty concerned with the study and treatment of the dental pulp. Overview Endodontics encompasses the study (practice) of the basic and clinical ...
s use EDTA solutions to remove inorganic debris (
smear layer In dentistry, the smear layer is a layer found on root canal walls after root canal instrumentation. It consists of microcrystalline and organic particle debris. It was first described in 1975 and research has been performed since then to evaluate i ...
) and lubricate the
root canal A root canal is the naturally occurring anatomic space within the root of a tooth. It consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root ...
s in endodontics. This procedure helps prepare root canals for
obturation In the field of firearms and airguns, obturation denotes necessary barrel blockage or fit by a deformed soft projectile (obturation in general is closing up an opening). A bullet or pellet, made of soft material and often with a concave base, ...
. Furthermore, EDTA solutions with the addition of a surfactant loosen up
calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Ma ...
s inside a root canal and allow instrumentation (canal shaping) and facilitate apical advancement of a file in a tight or calcified root canal towards the apex.


Eyedrops

It serves as a
preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
(usually to enhance the action of another preservative such as
benzalkonium chloride Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) and by the trade name Zephiran, is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs ha ...
or
thiomersal Thiomersal (INN), or thimerosal (USAN, JAN), is an organomercury compound. It is a well-established antiseptic and antifungal agent. The pharmaceutical corporation Eli Lilly and Company gave thiomersal the trade name Merthiolate. It has been u ...
) in ocular preparations and
eyedrops Eye drops or eyedrops are liquid drops applied directly to the surface of the eye usually in small amounts such as a single drop or a few drops. Eye drops usually contain saline to match the salinity of the eye. Drops containing only salin ...
.


Analysis

In evaluating
kidney function Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging. Functions of a healthy kidney include maintaining a person's fluid ...
, the chromium(III) complex
r(EDTA) R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Irelan ...
sup>− (as radioactive
chromium-51 Naturally occurring chromium (24Cr) is composed of four stable isotopes; 50Cr, 52Cr, 53Cr, and 54Cr with 52Cr being the most abundant (83.789% natural abundance). 50Cr is suspected of decaying by β+β+ to 50Ti with a half-life of (more than) 1. ...
(51Cr)) is administered
intravenously Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
and its filtration into the
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular ...
is monitored. This method is useful for evaluating
glomerular filtration rate Renal functions include maintaining an acid–base balance; regulating fluid balance; regulating sodium, potassium, and other electrolytes; clearing toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pre ...
(GFR) in
nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
. EDTA is used extensively in the analysis of blood. It is an anticoagulant for blood samples for CBC/FBCs, where the EDTA chelates the calcium present in the blood specimen, arresting the coagulation process and preserving blood cell morphology. Tubes containing EDTA are marked with
lavender ''Lavandula'' (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found in Cape Verde and the Canary Islands, and from Europe across to northern and easte ...
(purple) or pink tops. EDTA is also in tan top tubes for lead testing and can be used in royal blue top tubes for trace metal testing. EDTA is a slime dispersant, and has been found to be highly effective in reducing bacterial growth during implantation of
intraocular lens Intraocular lens (IOL) is a lens (optics), lens implanted in the human eye, eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as Phakic intraocular lens, phakic, otherwise it is a pseudop ...
es (IOLs).


Alternative medicine

Some alternative practitioners believe EDTA acts as an antioxidant, preventing
free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
s from injuring
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
walls, therefore reducing
atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...
. These ideas are unsupported by scientific studies, and seem to contradict some currently accepted principles. The U.S. FDA has not approved it for the treatment of atherosclerosis.


Cosmetics

In
shampoo Shampoo () is a hair care product, typically in the form of a Viscosity, viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in solid bar format. Shampoo is used by applying it to wet hair, massaging the product ...
s, cleaners, and other personal care products, EDTA salts are used as a sequestering agent to improve their stability in air.


Laboratory applications

In the laboratory, EDTA is widely used for scavenging metal ions: In
biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
and
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...
, ion depletion is commonly used to deactivate metal-dependent enzymes, either as an assay for their reactivity or to suppress damage to DNA,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, and polysaccharides. EDTA also acts as a selective inhibitor against dNTP hydrolyzing enzymes (
Taq polymerase ''Taq'' polymerase is a thermostable DNA polymerase I named after the thermophilic eubacterial microorganism '' Thermus aquaticus,'' from which it was originally isolated by Chien et al. in 1976. Its name is often abbreviated to ''Taq'' or '' ...
, dUTPase, MutT), liver
arginase Arginase (, ''arginine amidinase'', ''canavanase'', ''L-arginase'', ''arginine transamidinase'') is a manganese-containing enzyme. The reaction catalyzed by this enzyme is: : arginine + H2O → ornithine + urea It is the final enzyme of the ure ...
and horseradish peroxidase independently of metal ion
chelation Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
. These findings urge the rethinking of the utilisation of EDTA as a biochemically inactive metal ion scavenger in enzymatic experiments. In analytical chemistry, EDTA is used in
complexometric titration Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determinati ...
s and analysis of
water hardness Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...
or as a
masking agent A masking agent is a reagent used in chemical analysis which reacts with chemical species that may interfere in the analysis. In sports a masking agent is used to hide or prevent detection of a banned substance or illegal drug like anabolic ste ...
to sequester metal ions that would interfere with the analyses. EDTA finds many specialised uses in the biomedical labs, such as in
veterinary Veterinary medicine is the branch of medicine that deals with the prevention, management, diagnosis, and treatment of disease, disorder, and injury in animals. Along with this, it deals with animal rearing, husbandry, breeding, research on nutri ...
ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medic ...
as an anticollagenase to prevent the worsening of
corneal ulcers in animals A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the cornea involving loss of its outer layer. It is very common in dogs and is sometimes seen in cats. In veterinary medicine, the term ''corneal ulcer'' is a generic name ...
. In
tissue culture Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, su ...
EDTA is used as a chelating agent that binds to
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and prevents joining of
cadherins Cadherins (named for "calcium-dependent adhesion") are a type of cell adhesion molecule (CAM) that is important in the formation of adherens junctions to allow cells to adhere to each other . Cadherins are a class of type-1 transmembrane proteins, ...
between cells, preventing clumping of cells grown in liquid suspension, or detaching adherent cells for
passaging In biology, a subculture is either a new cell culture or a microbiological culture made by transferring some or all cell (biology), cells from a previous culture to fresh growth medium. This action is called subculturing or passaging the cells. Sub ...
. In histopathology, EDTA can be used as a decalcifying agent making it possible to cut sections using a microtome once the tissue sample is demineralised. EDTA is also known to inhibit a range of metallopeptidases, the method of inhibition occurs via the
chelation Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
of the metal ion required for catalytic activity. EDTA can also be used to test for
bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
of heavy metals in
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s. However, it may ''influence'' the bioavailability of metals in solution, which may pose concerns regarding its effects in the environment, especially given its widespread uses and applications. EDTA is also used to remove crud (corroded metals) from fuel rods in nuclear reactors.


Side effects

EDTA exhibits low acute toxicity with (rat) of 2.0 g/kg to 2.2 g/kg. It has been found to be both cytotoxic and weakly
genotoxic Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with mutagenicity, all mutagens are genotoxic, but some genotoxic s ...
in laboratory animals. Oral exposures have been noted to cause reproductive and developmental effects. The same study also found that both dermal exposure to EDTA in most cosmetic formulations and inhalation exposure to EDTA in aerosolised cosmetic formulations would produce exposure levels below those seen to be toxic in oral dosing studies.


Synthesis

The compound was first described in 1935 by
Ferdinand Münz Ferdinand Münz (1888-1969) was an Austrian chemist who first synthesized EDTA (ethylenediaminetetraacetic acid) at the IG Farben in 1935, patented both in Germany (anonymously) and in the USA (with his name), with the aim of producing a citric a ...
, who prepared the compound from ethylenediamine and
chloroacetic acid Chloroacetic acid, industrially known as monochloroacetic acid (MCA), is the organochlorine compound with the formula ClCH2CO2H. This carboxylic acid is a useful building block in organic synthesis. It is a colorless solid. Related compounds a ...
. Today, EDTA is mainly synthesised from ethylenediamine (1,2-diaminoethane),
formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
, and
sodium cyanide Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its hi ...
. This route yields the tetrasodium EDTA, which is converted in a subsequent step into the acid forms: :H2NCH2CH2NH2 + 4  CH2O + 4  NaCN + 4 H2O → (NaO2CCH2)2NCH2CH2N(CH2CO2Na)2 + 4  NH3 :(NaO2CCH2)2NCH2CH2N(CH2CO2Na)2 + 4 
HCl HCL may refer to: Science and medicine * Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia * Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development * Hollow-cathode lamp, a spe ...
→ (HO2CCH2)2NCH2CH2N(CH2CO2H)2 + 4 
NaCl Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...
This process is used to produce about 80,000 tonnes of EDTA each year. Impurities cogenerated by this route include
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid ( carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
and
nitrilotriacetic acid Nitrilotriacetic acid (NTA) is the aminopolycarboxylic acid with the formula N(CH2CO2H)3. It is a colourless solid that is used as a chelating agent, which forms coordination compounds with metal ions (chelates) such as Ca2+, Co2+, Cu2+, and Fe ...
; they arise from reactions of the
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
coproduct.


Nomenclature

To describe EDTA and its various protonated forms, chemists distinguish between EDTA4−, the
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
that is the
ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
, and H4EDTA, the
precursor Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of u ...
to that ligand. At very low pH (very acidic conditions) the fully protonated H6EDTA2+ form predominates, whereas at very high pH or very basic condition, the fully deprotonated EDTA4− form is prevalent. In this article, the term EDTA is used to mean H4−''x''EDTA''x''−, whereas in its complexes EDTA4− stands for the tetraanion ligand.


Coordination chemistry principles

In coordination chemistry, EDTA4− is a member of the
aminopolycarboxylic acid left, 120px, a metal complex with the EDTA anion 120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands. An aminopolycarboxylic acid (sometimes abbreviated APCA) is a chemical compound containing one or more nitrogen at ...
family of ligands. EDTA4− usually binds to a metal cation through its two amines and four carboxylates, i.e., it is It a
hexadentate A hexadentate ligand in coordination chemistry is a ligand that combines with a central metal atom with six bonds. One example of a hexadentate ligand that can form complexes with soft metal ions is TPEN. A commercially important hexadentate liga ...
("six-toothed")
chelating agent Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands ar ...
. Many of the resulting coordination compounds adopt
octahedral geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The oc ...
. Although of little consequence for its applications, these octahedral complexes are
chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from i ...
. The cobalt(III) anion o(EDTA)sup>− has been resolved into enantiomers. Many complexes of EDTA4− adopt more complex structures due to either the formation of an additional bond to water, ''i.e.'' seven-coordinate complexes, or the displacement of one carboxylate arm by water. The
iron(III) In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...
complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...
of EDTA is seven-coordinate. Early work on the development of EDTA was undertaken by
Gerold Schwarzenbach Gerold Karl Schwarzenbach (15 March 1904 – 20 May 1978) was a Swiss chemist. Schwarzenbach was born and grew up in Horgen, Switzerland. He studied chemistry at the ETH Zurich and graduated in 1928 with his dissertation ''Studien über die Salz ...
in the 1940s. EDTA forms especially strong complexes with Mn(II), Cu(II), Fe(III), Pb(II) and Co(III). Several features of EDTA's complexes are relevant to its applications. First, because of its high
denticity In coordination chemistry, denticity () refers to the number of donor groups in a given ligand that bind to the central metal atom in a coordination complex. In many cases, only one atom in the ligand binds to the metal, so the denticity equals ...
, this ligand has a high affinity for metal cations: : e(H2O)6sup>3+ + H4EDTA
e(EDTA) E, or e, is the fifth letter and the second vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''e'' (pronounced ); plur ...
sup>− + 6 H2O + 4 H+ ''K''eq = 1025.1 Written in this way, the equilibrium quotient shows that metal ions compete with protons for binding to EDTA. Because metal ions are extensively enveloped by EDTA, their catalytic properties are often suppressed. Finally, since complexes of EDTA4− are
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
ic, they tend to be highly soluble in water. For this reason, EDTA is able to dissolve deposits of
metal oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s and
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s. The p''K''a values of free EDTA are 0, 1.5, 2, 2.66 (
deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju. ...
of the four
carboxyl group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s) and 6.16, 10.24 (deprotonation of the two
amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
s).Hans Peter Latscha: ''Analytische Chemie.'' Springer-Verlag, 2013, , p. 303.


Environmental fate


Abiotic degradation

EDTA is in such widespread use that questions have been raised whether it is a
persistent organic pollutant Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversel ...
. While EDTA serves many positive functions in different industrial, pharmaceutical and other avenues, the longevity of EDTA can pose serious issues in the environment. The degradation of EDTA is slow. It mainly occurs
abiotic In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...
ally in the presence of sunlight. The most important process for the elimination of EDTA from surface waters is direct photolysis at wavelengths below 400 nm. Depending on the light conditions, the photolysis
half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...
of iron(III) EDTA in surface waters can range as low as 11.3 minutes up to more than 100 hours. Degradation of FeEDTA, but not EDTA itself, produces iron complexes of the triacetate (ED3A), diacetate (EDDA), and monoacetate (EDMA) – 92% of EDDA and EDMA biodegrades in 20 hours while ED3A displays significantly higher resistance. Many environmentally-abundant EDTA species (such as Mg2+ and Ca2+) are more persistent.


Biodegradation

In many industrial wastewater treatment plants, EDTA elimination can be achieved at about 80% using microorganisms. Resulting byproducts are ED3A and
iminodiacetic acid Iminodiacetic acid is the organic compound with the formula HN(CH2CO2H)2, often abbreviated to IDA. A white solid, the compound is a dicarboxylic acid amine (the nitrogen atom forms a secondary amino group, not an imino group as the name suggests ...
(IDA) – suggesting that both the backbone and acetyl groups were attacked. Some microorganisms have even been discovered to form nitrates out of EDTA, but they function optimally at moderately alkaline conditions of pH 9.0–9.5. Several bacterial strains isolated from sewage treatment plants efficiently degrade EDTA. Specific strains include ''
Agrobacterium radiobacter ''Agrobacterium radiobacter'' (more commonly known as ''Agrobacterium tumefaciens'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Sympto ...
'' ATCC 55002 and the sub-branches of Pseudomonadota like BNC1, BNC2, and strain DSM 9103. The three strains share similar properties of aerobic respiration and are classified as
gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
. Unlike photolysis, the chelated species is not exclusive to iron(III) in order to be degraded. Rather, each strain uniquely consumes varying metal–EDTA complexes through several enzymatic pathways. Agrobacterium radiobacter only degrades Fe(III) EDTA while BNC1 and DSM 9103 are not capable of degrading iron(III) EDTA and are more suited for
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
, barium,
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
and manganese(II) complexes. EDTA complexes require dissociation before degradation.


Alternatives to EDTA

Interest in environmental safety has raised concerns about biodegradability of aminopolycarboxylates such as EDTA. These concerns incentivize the investigation of alternative aminopolycarboxylates. Candidate chelating agents include nitrilotriacetic acid (NTA), iminodisuccinic acid (IDS), polyaspartic acid, ''S,S''-ethylenediamine-''N'',''N''′-disuccinic acid (EDDS), methylglycinediacetic acid (MGDA), and L-Glutamic acid ''N'',''N''-diacetic acid, tetrasodium salt (GLDA).


Iminodisuccinic acid (IDS)

Commercially used since 1998, iminodisuccinic acid (IDS) biodegrades by about 80% after only 7 days. IDS binds to calcium exceptionally well and forms stable compounds with other heavy metal ions. In addition to having a lower toxicity after chelation, IDS is degraded by '' Agrobacterium tumefaciens'' (BY6), which can be harvested on a large scale. The enzymes involved, IDS epimerase and C−N lyase, do not require any
cofactors Cofactor may also refer to: * Cofactor (biochemistry), a substance that needs to be present in addition to an enzyme for a certain reaction to be catalysed * A domain parameter in elliptic curve cryptography, defined as the ratio between the order ...
.


Polyaspartic acid

Polyaspartic acid Polyaspartic acid (PASA) is a biodegradable, water-soluble condensation polymer based on the amino acid aspartic acid. It is a biodegradable replacement for water softeners and related applications. PASA can be chemically crosslinked with a wid ...
, like IDS, binds to calcium and other heavy metal ions. It has many practical applications including corrosion inhibitors, wastewater additives, and agricultural polymers. A Polyaspartic acid-based
laundry detergent Laundry detergent is a type of detergent (cleaning agent) used for cleaning dirty laundry (clothes). Laundry detergent is manufactured in powder (washing powder) and liquid form. While powdered and liquid detergents hold roughly equal share o ...
was the first laundry detergent in the world to receive the EU flower ecolabel. Calcium binding ability of polyaspartic acid has been exploited for targeting of drug-loaded nanocarriers to bone. Preparation of hydrogels based on polyaspartic acid, in a variety of physical forms ranging from
fiber Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorpora ...
to
particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from ...
, can potentially enable facile separation of the chelated ions from a solution. Therefore, despite being weaker than EDTA, polyaspartic acid can still be regarded as a viable alternative due to these features as well as
biocompatibility Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...
, and
biodegradability Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
.


''S'',''S''-Ethylenediamine-''N'',''N''′-disuccinic acid (EDDS)

A structural isomer of EDTA, ethylenediamine-''N'',''N''′-disuccinic acid (EDDS) is readily biodegradable at high rate in its ''S'',''S'' form.


Methylglycinediacetic acid (MGDA)

Trisodium dicarboxymethyl alaninate, also known as methylglycinediacetic acid (MGDA), has a high rate of biodegradation at over 68%, but unlike many other chelating agents can degrade without the assistance of adapted bacteria. Additionally, unlike EDDS or IDS, MGDA can withstand higher temperatures while maintaining a high stability as well as the entire pH range. MGDA has been shown to be an effective chelating agent, with a capacity for mobilization comparable with that of
nitrilotriacetic acid Nitrilotriacetic acid (NTA) is the aminopolycarboxylic acid with the formula N(CH2CO2H)3. It is a colourless solid that is used as a chelating agent, which forms coordination compounds with metal ions (chelates) such as Ca2+, Co2+, Cu2+, and Fe ...
(NTA), with application to water for industrial use and for the removal of calcium oxalate from urine from patients with
kidney stone Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
s.


Methods of detection and analysis

The most sensitive method of detecting and measuring EDTA in biological samples is selected reaction monitoring
capillary electrophoresis Capillary electrophoresis (CE) is a family of electrokinetic separation methods performed in submillimeter diameter capillaries and in micro- and nanofluidic channels. Very often, CE refers to capillary zone electrophoresis (CZE), but other elect ...
mass spectrometry (SRM-CE/MS), which has a
detection limit The limit of detection (LOD or LoD) is the lowest signal, or the lowest corresponding quantity to be determined (or extracted) from the signal, that can be observed with a sufficient degree of confidence or statistical significance. However, the ...
of 7.3 ng/mL in human plasma and a quantitation limit of 15 ng/mL. This method works with sample volumes as small as 7–8 nL. EDTA has also been measured in non-alcoholic beverages using
high performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pa ...
(HPLC) at a level of 2.0 μg/mL.


In popular culture

In the movie
Blade A blade is the portion of a tool, weapon, or machine with an edge that is designed to puncture, chop, slice or scrape surfaces or materials. Blades are typically made from materials that are harder than those they are to be used on. Histor ...
(1998), EDTA is used as a weapon to kill vampires, exploding when in contact with vampire blood.


References


External links


EDTA: Molecule of the Month

EDTA Determination of Total Water Hardness
* {{DEFAULTSORT:Ethylenediaminetetraacetic Acid Acetic acids Amines Antidotes Chelating agents Photographic chemicals Preservatives E-number additives Hexadentate ligands Ophthalmology drugs