Metal chelaters

More water soluble than di-methylglyoxime less subject to coprecipitation with metal chelate. 

CA Liquid-Liquid Extractions Involving Metal Chelators... 

Scheme for the liquid-liquid extraction of a metal ion by a metal chelator. 

Liquid-liquid extractions using ammonium pyrrolidine dithiocarbamate (APDC) as a metal chelating agent are commonly encountered in the analysis of metal ions in aqueous samples. The sample and APDC are mixed together, and the resulting metal-ligand complexes are extracted into methyl isobutyl ketone before analysis. 

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

F. Dwyer, Chelatingdgents and Metal Chelates, Academic Press, Inc., New York, 1964. 

Pentanedione is widely used in extraction processes for the separation and purification of metals because of its abiUty to form covalent metal chelates. It is also used as an intermediate in the production of heterocycHc substances and dyes, as a fuel additive (324), and in metal plating and resin modification. 

Salt Formation and Metal Chelation, Most a-ainiao acids form salts in alkaline and acidic aqueous solutions (88). For example, a-amino acids form inner complex salts with copper. 

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

Metal chelation is also a means of insoliihilizing organic molecules. For example. Cl Pigment Green 10 [51931 -46-5] (138) (Cl 12775) is a 2 1 nickel complex of a bidentate o-hydroxyazo ligand. 

Table 2. Concentration Formation Constants of Metal Chelates...

Fig. 4. pM vs pH for A Cu(II), and B Mn (IT) EDTA chelates. For each family of curves, the lowest curve represents 1% the second, 10% and the top curve, 100% of free ligand species ia excess of the amount needed to form the metal chelate. Broken lines represent soHd—solution equiUbria for... 

The concentration of the metal ion can be controlled by adjusting the ratio of the concentrations of free ligand and metal chelate. If both species are present in appreciable amounts, moderate changes in either concentration have Httie effect on the ratio. The concentration of the metal ion can thus be buffered in a manner analogous to the buffeting of pH by the presence of a weak acid and its anion... 

Deposits of an insoluble salt can be dissolved as a salt of the metal chelate. 

The ligand pATa values and transition metal chelate stability constants of arylisoxazoles were detected photometrically and the stability of the complexes studied (79JlCi25i). 

In metal chelate adsorption chromatography a metal is immobilised by partial chelation on a column which contains bi- or tri- dentate ligands. Its application is in the separation of substances which can complex with the bound metals and depends on the stability constants of the various ligands (Porath, Carlsson, Olsson and Belfrage Nature 258 598 I975 Loennerdal, Carlsson and Porath FEES Lett 75 89 1977). 

C. F. Bell, Principles and Applications of Metal Chelation, Oxford University Press, Oxford, 1977, 147 pp. 

The Knorr pyrazole synthesis has been extensively utilized in the preparation of a number of pyrazoles as metal chelators, photographic dyes, herbicides, and biologically active... 

The metal chelating 2,2"-bipyridines, useful in material science, can be obtained by this method.For example, bis-triazines 92, in the presence of two equivalents of enamine 67, will produce bipyridines 93. 

Whereas vicinal hydroxy, mercapto, and hydroselenoaldimines of azoles strongly prefer the aminomethylene tautomeric form (Section II,E,2), their metal chelates 380 are characterized by.pronounced equalization of bond lengths within the chelate ring, which makes their structures similar to those expected for the aldimine tautomeric type. 

T. G. Takhirov X-Ray Structural Investigation of Stereochemi-cally Nonrigid Tetracoordinated Metal-Chelates of Zn(II), Cd(II), Hg(II) and Ni(II) on the Base of Derivatives of 4-... 

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