Chelating agents Subject

In the presence of the chelating agent and the insoluble salt, MX, pM of the solution is subject to both the metal buffering and the solubiUty equiUbria. Equating the right-hand sides of the equations 26 and 29 and rearranging gives... 

Palmer 1989 Robinson et al.1983). However, the ratio was almost certainly affected by initial chelation with Ca-DPTA, followed by daily intravenous therapy with the chelating agent, Zn-DPTA, treatments that would have increased the urinary excretion of americium (Breitenstein and Palmer 1989). The above not withstanding, the observations made on this subject demonstrate that fecal excretion was an important pathway of excretion in this subject long after mechanical clearance of americium from the respiratory tract would have been complete. This is consistent with observations made in nonhuman primates that show that americium is excreted into bile (see Section 3.4.4.4). However, the extent to which the biliary excretion pathway in humans might resemble that of nonhuman primates is not known. 

Proteins modified with 2-iminothiolane are subject to disulfide formation upon sulfhydryl oxidation. This can cause unwanted conjugation, potentially precipitating the protein. The addition of a metal-chelating agent such as EDTA (0.01-0.1M) will prevent metal-catalyzed oxidation and maintain sulfhydryl stability. In the presence of some serum proteins (i.e., BSA) a 0.1M concentration of EDTA may be necessary to prevent metal-catalyzed oxidation, presumably due to the high contamination of iron from hemolyzed blood. 

A very important ligand (or chelating agent) for titrimetric analysis is the ethylenediaminetetraacetate (EDTA) ligand. It is especially useful in reacting with calcium and magnesium ions in hard water such that water hardness can be determined. The next section is devoted to this subject. 

Although most clinicians support chelation for symptomatic patients with elevated blood lead concentrations, the decision to chelate asymptomatic subjects is more controversial. Since 1991, the Centers for Disease Control and Prevention (CDC) has recommended chelation for all children with blood lead concentrations of 45 mcg/dL or greater. However, a recent randomized, double-blind, placebo-controlled clinical trial of succimer in children with blood lead concentrations between 25 mcg/dL and 44 mcg/dL found no benefit on neurocognitive function or long-term blood lead reduction. Prophylactic use of chelating agents in the workplace should never be a substitute for reduction or prevention of excessive exposure. 

We will not go in depth into the subject of antioxidants (12), which is more a part of preformulation than a stress test, but the autoxidation mechanism does suggest that oxidation can be inhibited by peroxy radical scavengers (chain-breaking antioxidants) like phenol antioxidants, by heavy metal chelating agents, and by peroxide inactivating substances (preventive antioxidants). 

A number of procedures for the determination of metals and biological samples call for the extraction of the metal with an organic chelating agent in order to remove interferences and concentrate the metal to enable detection of low levels. The urine or blood sample may be first subjected to wet ashing to enable extraction of the metal. Beryllium from an acid-digested blood or urine sample may be extracted by acetylacetone into methylisobutyl ketone prior to atomic absorption analysis. Virtually all of the common metals can be determined by this approach using appropriate extractants. 

A procedure was developed for the determination of total and labile Cu and Fe in river surface water. It involved simultaneous solvent extraction of the metals as diethyldithio-carbamates (ddc) and tfac complexes. The complexes were extracted by isobutyl methyl ketone (ibmk) and the solution subjected to flame atomic absorption spectrometry. Variables such as pH, metal complex concentration, reaction time, ibmk volume and extraction time were optimized. Prior to the solvent extraction a microwave-assisted peroxydisulfate oxidation was used to break down the metallorganic matter complexes in the river surface waters . Trifluoroacetylacetone was used as a chelation agent for the extraction and quantitative determination of total Cr in sea water. The chelation reaction was conducted in a single aqueous phase medium. Both headspace and liquid phase extractions were studied and various detection techniques, such as capillary GC-ECD, EI-MS (electron-impact MS) and ICP-MS, were tested and compared. The LOD was 11-15 ngL Cr for all the systems examined. The method provided accurate results with EI-MS and ICP-MS, while significant bias was experienced with ECD °. ... 

---