Sequestrants EDTA,

Water Softeners. Sequestrants (EDTA or polyphosphates) are used, especially in circulating-liquor dyeing with hardness-sensitive dyes [5, p. 273-274],... 

Sodium cyanide also is used in chemical synthesis. As previously mentioned, sodium cyanide is used to produce the sequestrant EDTA [82]. Chloroacetic acid reacts with sodium cyanide in the presence of soda ash to yield cyano-acetic acid. Sodium cyanide reacting with a-chloromethylnaphthalene followed by hydrolysis yields a-naphthaleneacetamide and the corresponding carboxylic acid these are two of several common plant hormones, growth acceler-... 

Sequestrants. These protect SBR latex from ions through complex formation. EDTA (ethylenediamine tetraacetic acid) is the most common. 

Ligands bite at one or more points. Chelants bite at two or more points, so all ligands are not necessarily chelants. Chelants forming water-soluble complexes with metal ions are called sequestrants (but not all sequestrants are chelants). The most commonly employed BW chelant, ethylenediaminetetraacetic acid (EDTA) produces coordination complexes with four points of attachment and is termed a tetraden-tate ligand. 

Phosphonates exhibit all the properties of polyphosphates, such as threshold effect, crystal distortion, and sequestration, but are superior in their effectiveness. They provide good chelates for calcium, magnesium, iron, and copper and are commonly used where iron fouling is a problem. Their sequestering properties are generally superior to other common chelants, such as EDTA and NTA. 

HMDTMP] is an excellent DCA for calcium sulfate, but a relatively poor sequestrant compared to other phosphonates (although still satisfactory compared to EDTA and NTA, which have similar... 

The sodium and calcium salts of EDTA (ethylenediaminetetraacetic acid, Fig. 9.3.1.) are common sequestrants in food products. A three-dimensional representation of EDTA is shown in color Fig. 9.3.2. The EDTA ion is an especially effective sequestrant, forming up to six coordinate covalent bonds with a metal ion. These bonds are so named because a lone pair of electrons on a single atom serves as the source of the shared electrons in the bond between the metal ion and EDTA. The two nitrogen atoms in the amino groups and the oxygen... 

A common form of EDTA used as a preservative is calcium disodium EDTA (CaNa2EDTA). What metals will this form of the sequestrant scavenge effectively The dissolution of the solid will yield calcium ions, sodium ions, and the EDTA anion. Any metal more effectively complexed than calcium will be readily scavenged, including all ions listed in Table 9.1 except silver (Ag+) and magnesium (Mg2+). (In the absence of the calcium counterion, as in the case of the acid form of EDTA, chelation of calcium in the body can occur. In fact, EDTA administered orally is an FDA-approved treatment for calcium deposits in the bloodstream that lead to cardiovascular disease.) Citric acid (Fig. 9.3.3) is another sequestrant of metal ions in foodstuffs. 

It forms numerous salts, some of which are listed in Ref 4, p 466 L. It has been used for determination of about 40 metals and several anions (Ref 2) also used for decontamination of radioactive surfaces and removal of insol deposits of Ca Mg soaps (Ref 4). Its application in volumetric titrations is discussed in Ref 3. Accdg to Alrose Chem Co, PO Box 1294, Providence, RI, EDTA dissolves Ca oxalate and serves as a sequestrene. The term sequestration may be used for any instance in which an ion is prevented from exhibiting its usual props due to close combination with an added material (Ref 4, p 1013 L) ... 

Secondary antioxidants, i.e., sequestrants or chelators, are important compounds in the prevention of lipid oxidation. The effect of chelators tested varied with the different compounds. Of those chelators tested, ethylenediaminetetraacetic acid (EDTA, tetrasodium salt) and sodium phytate were the most effective inhibitors of lipid oxidation (so indicated by low hexanal and TEARS values) and MFD (as seen by high CBB and low PIT and CBD intensity values), see Table 5. Sodium phytate was previously shown to chelate iron and thus, was proposed as a food antioxidant(7J). Sodium citrate at a concentration of 500... 

Chemical - complex formation. Earlier we discussed the complexation which can occur between the chelating agent EDTA and heavy metals or the sequestration of lipids in cholestyramine resins. The immune system has antibody-antigen complexes formed which can help in the elimination of the antigen (xenobiotic). 

EDTA has been determined in a wide variety of sample matrices by HPLC. These matrices include waste waters, natural waters, sediments, fertilizers, chemical cleaning solutions, radioactive waste solutions, and pharmaceutical preparations. Chinnick reported the separation and identification of EDTA and other aminopolycarboxylic acid sequestrants by a high performance liquid chromatographic (HPLC) method [57]. 

Chelating agents or sequestrants remove metallic ions, especially copper and iron, that are powerful prooxidants. Citric acid is widely used for this purpose. Amino acids and ethylene diamine tetraacetic acid (EDTA) are other examples of chelating agents. 

Since there are synergistic effects between antioxidants, commercial preparations usually contain mixtures of these antioxidants. As oxidative rancidity is strongly catalyzed by some heavy metal ions, in particular QT+, antioxidant mixtures often contain sequestrants (e.g., citric acid and ethylenediaminetetraacetic acid (EDTA)) in order to complex these ions. Reductants such as ascorbic acid, which decrease the local concentration of oxygen, are also able to decrease the formation of peroxy radicals. 

In sequestration (chelation) the hardness ions are bound to the builder in the form of soluble complexes. Phosphates, citrates, and nitrilotriacetic acid (NTA) are examples of this class of builder compound. Table 8.3 lists the calcium binding capacities of various builders. Other strongly chelating compounds exist, such as phosphonates and EDTA, but they are generally not extensively used in HDLDs. The most efficient builder is sodium tripolyphosphate (STPP). Unfortunately, tripolyphosphate has been identified as a possible cause of eutrophication in lakes and rivers. It is severely controlled and even banned in several countries. As a result, most countries in North America and Europe have converted to nonphosphate formulations. Other regions are also gradually imposing restrictions on the use of phosphates. 

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