Chromium-EDTA chelate

As it was not known what kind of organic matter acts as the major ligand for chromium in seawater, Nakayama et al. [38] used ethylene diaminetetra-acetic acid (EDTA) and 8-quinolinol-4-sulfuric acid to examine the collection and decomposition of organic chromium species, because these ligands form quite stable water-soluble complexes with chromium (III), although they are not actually present in seawater. Both of these chromium (III) chelates are stable in seawater at pH 8.1 and are hardly collected with either of the hydrated oxides. The organic chromium species were then decomposed to inorganic... 

Ding et al. [88] used anion-exchange chromatog-raphy-ICP-MS to determine different forms of chromium in chromium picolinate products which are used as dietary supplements and appear to assist in weight loss. A Dionex AS7 anion-exchange column was used to separate Cr(III)-EDTA chelate and Cr(VI) in the supplements. Only 1% total chromium recoveries were obtained and this was attributed to retention of the chromium species on-column. The use of RP-HPLC proved to be more effective and complete chromium recoveries were obtained, based on the amounts stated on the manufacturer s product labels. 

Kartal and Kose (2003) investigated the removal of arsenic from CCA-treated wood with common chelating agents (EDTA, nitrilotriacetic acid (C6H9NO6), and oxalic acid). Dual mixtures of EDTA and oxalic acid and nitrilotriacetic and oxalic acids removed about 100% of the arsenic from sawdust of the wood. However, only about 80 % of the arsenic was removed from wood chips with the same dual solutions. Once the arsenic, copper, chromium, and any other toxins have been removed from the wood, it could be used as a biofuel. 

Results of an in vitro experiment in this study indicated that the midsection had greater uptake than the duodenum or ileum and that oxalate significantly (p<0.05) increased, while phytate significantly (p<0.05) decreased the transport of chromium(III) across all three sections, paralleling the in vivo results. Ethylenediamine tetraacetic acid (EDTA) and citrate were also tested in the in vitro system, but were found to have no effect on chromium(III) intestinal transport therefore, these chelating agents were not tested in vivo (Chen et al. 1973). 

A simple and rapid method for the iodometric determination of microgram amounts of chromium(ni) in organic chelates is based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the umeacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate . Iodometric titration was also used for determination of the effective isoascorbate (see 2) concentration in fermentation processes . The content of calcium ascorbate can be determined with high sensitivity by complexometric titration with edta, which is superior to iodometry. The purity of /3 -diketonate complexes of Al, Ga, In and Ni was determined by complexometric titration with edta at pH 5.5-3, with RSD < 0.01 for determining 5-30% metal ion. Good analytical results were obtained by a similar procedure for the metal content of 15 lanthanide organic complexes. ... 

Chromel is an alloy composed of nickel, iron, and chromium. A 0.6472-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05182 M EDTA was mixed with an equal volume of the diluted sample, all three ions were chelated, and a 5.11-mL back-titration with 0.06241 M copper(II) was required. The chromium in a second 50.0-mL aliquot was masked through the addition of hexamethylenetetramine titration of the Fe and Ni required 36.28 mL of 0.05182 M EDTA. Iron and chromium were masked with pyrophosphate in a third 50.0-mL aliquot, and the nickel was titrated with 25.91 mL of the EDTA solution. Calculate the percentages of nickel, chromium, and iron in the alloy. 

The reaction of superoxotitanium(IV) with a number of substrates has been monitored by stopped-flow techniques/ In 1 M perchloric acid, the oxidation of iodide and bromide proceeded with second-order ratde constants of 1.1 x 10 M s and 2M s respectively. It is proposed that the reduction of superoxotitanium(IV) proceeds by a one-electron mechanism. Based on proton dependences, the species TiO " is more reactive than the protonated form Ti02(0H)2. The chromium chelate, bis(2-ethyl-2-hydroxybutyrato)oxochro-mate(V), is reduced by iodide, generating a Cr(IV) intermediate. The reaction is considered to proceed through formation of an iodine atom (T) for which both Cr(V) and Cr(IV) compete. In aqueous solution, [Co(EDTA)] forms a tight ion pair with I . Upon irradiation of this ion pair at 313 nm, reduction of [Co(EDTA)] to [Co(EDTA)] occurs with oxidation of 1 to IJ. The results may be interpreted on the basis of a mechanism in which [Co(EDTA)] and V are the primary photoproducts where the latter subsequently disproportionate to I3 and 1 . The kinetics and mechanism of the oxidation of 1 by a number of tetraaza macrocyclic complexes of Ni(III) have been reported. Variations in rate constants and reaction pathways are attributable to structural differences in the macrocyclic ligands. Of interest is the fact that with some of the Ni(III) complexes, spectrophotometric evidence has been obtained for an inner-sphere process with characterization of the transient [Ni(III) L(I)] intermediates. Iodide has also been used as a reductant for a nickel(III) complex of R-2-methyl-1,4,7-triazacylononane. In contrast to the square-planar macrocycles, the octahedral... 

The formation of malonate and oxalate complexes from [Cr(OH2)6] + involves rate-determining chromium-water bond breaking in an ion-pair in each case. Activation parameters for these two reactions, for formation of the monoglycine complex, and for water exchange at chromium(iii) are all rather similar. The formation of edta complexes of chromium(iii) is more complicated, involving several water displacement and chelation steps. Rates and activation parameters are reported for the tridentate to quinquedentate conversion ... 

The effects of a variety of anions on chelation steps in the chromium(iii)-edta reaction have been studied. ... 

The extent of precursor complex formation is an important factor in determining the relative rates of chromous reduction of complexes [(NH3)5CoYH ], where Y is 0-bound ida " or edta . With [(NH3)5Co(ida)] the precursor involves chelation at Cr " and leads to the tridentate-bound ligand, whereas protonated cobalt(III) reagents yield only monodentate chromium(III) products. 

Formation reactions of chromium(iii)-carboxylate complexes often do not follow the normal kinetic pattern, as has been illustrated by the study of the reaction of [Cr(NH3)6(OH2)] + with amino-acids. Here reaction takes place exclusively by a carbon dioxide-catalysed pathway in which ammonia is displaced to give an intermediate carbonato-chelate. The ratedetermining step in the formation of chromium(rii)-edta complexes is a ligand interchange process. The dependence of rates on pH can be explained in terms of the relative reactivities of variously protonated forms of edta and of the [Cr(OH2)e] + and [Cr(OH2)s(OH)] + cations. The chelation step in the conversion of the quadridentate chromium(m)-edta complex to the quinquedentate form in aqueous solution has been studied over the pH range 0—12. From the rate-pH profile (see Figure) it is apparent that... 

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