Heat EDTA complexes

Insoluble metal salts are estimated by back titration the sample is heated with excess EDTA to form the soluble EDTA complex of the metal and then the excess EDTA is titrated with salt solutions containing Mg + or Zn- of known concentration. 

There are a number of examples of homogeneous precipitation of hydroxides based on slow cation release, such as destruction of the Fe-EDTA complex with H2O2 (see Ref. 33). In CD, the only well-defined example of this is heating an ammonia complex (e.g. of Cd ). The loss of ammonia by volatilization will gradually increase the concentration of free Cd ions. 

The relative ability of the transition metal ions to form complex ions is Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ > Zn2+ for the divalent cations and Cr3+ — Mn3+ > Fe3+ < Co3+ for the trivalent cations. The strongest complexing divalent cation is Cu(II). Fe(III) is the weakest complexing trivalent transition metal ion, but is stronger than other trivalent cations such as Al3+ and the lanthanides. The heats of hydration (Table 3.2), strengths of EDTA complexes (Table 3.5), and solubility products of metal hydroxyoxides (Table 3.3) also follow this general order, with water, EDTA, and OH" as the respective ligands. Stability constants less than I09 indicate the weaker ion-ion interaction of ion pairs. 

Then without having added any sample, heat to about 40°C and titrate with 0.01 M sodium edetate xmtil the violet color changes to full blue. The test solution prepared in step one contains both zinc and the indicator Erio-chrome Black and it will form a violet complex. But when the test solution is titrated with EDTA in the second step of analysis the stronger EDTA complex will deplete zinc ions of tiie solution and the indicator complex making it change the color to its metal free blue form, since titration is carried out to blue and EDTA is complexed with zinc. 

Hydration of lanthanide complexes. X-ray diffraction studies of the solid complexes of KLn(EDTA)(H20),c showed the number of water molecules in the coordination sphere to be three for the lighter lanthanides and two for the heavier ones for total coordination numbers of nine and eight, respectively, since EDTA is hexadentate (Hoard et al. 1967). Ots (1973) measured a maximum at europium for the heat capacity change AC° for the formation of lanthanide-EDTA complexes. This maximum was taken as a strong evidence for hydration equilibrium between the complexed species,... 

An excess of ethylenedlamlnetetraacetlc acid (EDTA). causes lead to be soluble In chloride solutions (Cl) due to formation of the very stable EDTA-lead complex. Silver (l) and thallium (l) chlorides remain Insoluble and can be separated from lead. Mercury (I) also forms a soluble EDTA complex imder these conditions. The presence of citrate also keeps lead from precipitating from dilute chloride solutions. Mukherjl and Dey have used this to separate lead from silver (m4). In their procedure an excess of sodium citrate Is added to the mixture containing silver and lead nitrate. The Insoluble citrates of lead and silver which are at first precipitated redlssolve upon gentle heating as complex citrates. Upon addition of dilute hydrochloric acid silver chloride precipitates. Lead may be removed from the filtrate as lead chromate. 

Isothermal polymerizations are carried out in thin films so that heat removal is efficient. In a typical isothermal polymerization, aqueous acrylamide is sparged with nitrogen for 1 h at 25°C and EDTA (C2QH2 N20g) is then added to complex the copper inhibitor. Polymerization can then be initiated as above with the ammonium persulfate—sodium bisulfite redox couple. The batch temperature is allowed to rise slowly to 40°C and is then cooled to maintain the temperature at 40°C. The polymerization is complete after several hours, at which time additional sodium bisulfite is added to reduce residual acrylamide. 

The simultaneous determination of Co and Ni is also made at pH 8 in the presence of pyrophosphate. The EDTA is added to the mixture of coloured complexes of these metals to bind the Cu and Zn admixtures into the inactive complexes. The optical density of the solution is measured at 530, 555 and 580 nm. The solution is heated to the boiling point to destmct the complex formed by Ni with PAR, and then is cooled. Again the measurements of optical density ai e performed at the same wavelengths. The Ni concentration is calculated from the variation in the optical density, and the Co concentration is calculated from the final values of optical density. The detection limits for these metals are 4 and 2 p.g/dm, respectively. 

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

An affinity sorbent based on WPA-PG carrying immobilized human IgG was applied to the isolation of the first component of the complement (Cl) from human serum and for its separation into subcomponents Clr, Cls and Clq by the one-step procedure [126,127]. Cl was quantitatively bound to the sorbent at 0 °C. The activities of subcomponents Clq and Clr2r2 in the unbound part of the serum were found to be 0.8% and 3.3% of the initial activities in serum. This fraction, therefore, could be used as a R1 reagent for determining the hemolytic activity of Cl. Apparently, the neighboring macromolecules of immobilized IgG resemble to some extent an immune complex, whereas Cl formation is facilitated due to the mobility of polymer chains with the attached IgG macromolecules (Cl is usually dissociated in serum by 30%). After activation of bound Cl by heating (30 °C, 40 min) the activated subcomponent Clr is eluted from the sorbent. Stepwise elution with 0.05 mol/1 EDTA at pH 7.4 or with 0.05 mol/1 EDTA + 1 mol/1 NaCl at pH 8.5 results in a selective and quantitative elution of the activated subcomponent Cls and subcomponent Clq. 

Based on this observation, calcium released from this complex requires high-temperature heating in combination with a calcium chelating and/or precipitating agent such as EDTA, EGTA, citrate buffer, or urea. Because these reagents are chelators of divalent... 

Figure 34. The 260-ntn absorbance melting curves (first heating) of poly(dA-dT) and its netropsin complex. Nttc/D — 50, 25, 18, and 10 in 0.1 M cacodylate, 4.4mM EDTA, H.O, pH 7.4. The polv(dA-dT) concentration was fixed at 0.545mM in phosphates and the curves are normalized to an absorbance of 1.0...

Figure 35. The temperature dependence (first heating) of the 360-MHz proton NMR spectra (5 to 9 ppm) oj the netrop-sin poly(dA-dT) complex, Nuc/D — 50, in 0.1 cacodylate, 4.4m5A EDTA, 2HtO, pH 7.5 between 53° and 68.5°C. The asterisks designate some of the minor resonances from base pairs centered at the binding site.

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