Metallic buffers

Metal Buffering. The equation for the formation constant of the reaction... 

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... 

Controlled metal complexation — While uncontrolled metal complex -ation can be a major source of problems, controlled complexation is a potentially useful selectivity modifier. The key is to evaluate the effects of only one metal at a time, which in turn requires that your sample be stripped of metals in preparation for your experimental treatment. The EDTA-imidazole treatment described above can be used for this purpose. For evaluating the effects of ferric iron or calcium, buffer exchange the treated sample into 0.05 M MES, pH 6, then add the metal salt of choice to a concentration of 5 mM. For other metals, buffer exchange the treated sample into 0.05 M Tris, pH 8, then add the metal salt of choice to 5 mM. 

ISEs with both these groups of systems exhibit Nernstian response to the Ca activity in the range 10" to 10 M in metal buffers with a slope of d isE/d log flca = 0.029 V. They can be used in the presence of 50 mM Na" for down to micromolar concentrations of Ca. The potentials of these ISEs do not depend on the hydrogen ion activity in the pH range 5.5 to 9 [146]. 

Selected entries from Methods in Enzymology [vol, page(s)] General Methods Preparation of metal-free water, 158, 3 elimination of adventitious metals, 158, 6 metal-free dialysis tubing, 158, 13 metal-free chromatographic media, 158, 15 preparation of metal-free enzymes, 158, 21 metal-buffered systems,... 

In a metal buffer (that is, a given mixture of cation and chelating agent)... 

Many additional complexities can occur in reactions of this type due to the presence of more than one complex in solution and to metal-buffer interactions which can lead to additional metal equilibria involving the buffer anion and even to mixed ligand complex formation. 

Raaflaub.Jurg, Applications of Metal Buffers and Metal Indicators in... 

Plots (b) and (e) show the free metal surface of the system (plotted as pM). These show pM increasing (i.e. free metal concentration decreasing) very rapidly as one moves more into the CLASP-w region (i.e. trace metal in presence of large ligand excess). The metal-buffering capability of the system is clearly depicted in the contour map (e). For example, the lines, or portions of lines, which are parallel to the C axis, describe... 

Figure 4.4.7 Indication of the distribution of toxicity found by using ToxScreen II (pro organic buffer) and Metal Detector in the River Ribble estuary during the ebb tide. No toxicity was found with either ToxScreen II pro-metal buffer or with the standard Microtox test (Roig el al., 2007)...

Non-volatile residue, heavy metals, buffering capacity, reducing substances. 

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