EDTA-Cu complex

Sketch the spectrophotometric titration curve for the titration of a mixture of 5.00 X 10 M Bi + and 5.00 X 10 M Cu + with 0.0100 M EDTA. Assume that only the Cu +-EDTA complex absorbs at the selected wavelength. 

A superoxide dismutase activity had been reported for the Fe-EDTA complex in contrast with the inactivity of the Cu-EDTA complex. It was shown, on the contrary, that Fe-EDTA, instead of catalysing the dismutation of OJ, interferes with the reduction of nitroblue tetrazolium and of Fe(III)-cytochrome c in the assays of the dismutase activity... 

Recently, Feldmann and Melroy [131] utilized a quartz microbalance technique to simultaneously determine the net current and the partial anodic and cathodic currents in a single complete electroless copper bath. The cathodic current is calculated by converting the deposition rate measured with the microbalance into the unit of current, while the anodic current is computed by subtracting the cathodic current from the net current measured directly on the microbalance electrode. Using this technique, Feldmann and Melroy showed that the potential at which the reduction of the Cu-EDTA complex begins at 70 °C shifts by as much as 0.3 V in positive direction upon addition of formaldehyde. It was also shown that at a given potential, the rate of copper deposition increases with increasing formaldehyde concentration (Fig. 23). The observed catalytic effect of formaldehyde is attributed to an interaction between formaldehyde and the Cu-EDTA complex, possibly to the formation of Cu(EDTA)/formaldehyde complex. However, the detailed mechanism of this catalytic effect has not been clarified. 

Wiese and Weil [132], who used the same technique combined with fast solution exchange, confirmed the catalytic effect of formaldehyde on the reduction of the Cu-EDTA complex. They also observed that the anodic oxidation of formaldehyde... 

Ferro-Garcia et al. [187] noted that EDTA complexation (see the section on nickel above) may not have the beneficial effect of eliminating the electrostatic repulsion between a positively charged surface and Cu"" (as well as Zn " and Cd- ) cations. This is illustrated in Table 5 and was rationalized by postulating that, in contrast to the smaller inorganic complexes, the Cu-EDTA complex may be excluded from a large fraction of pores in the olive-stone-derived microporous carbon used (with 60% of pores less than 7.5 nm in diameter). 

The third spectrum (c) was obtained from copper chloride dissolved in hydrated trioctylammonium 2-ethylhexanoate in toluene (the mixed extractant). It has a broad maximum absorbance at 725 nm, its symmetry is similar to that of copper carboxylate, and bonding of copper can be assumed to occur via the carboxylic oxygens in a manner similar to that of the dimer. Spectrum (c) bears an even greater similarity to that of the Cu-EDTA complex, the maximum absorption being at 734 nm, and which is known to have a distorted octahedral structure [12]. It is easy to convert the carboxyT ate dimer into a mixed complex. On adding trioctylamine to copper carboxylate, the maximum absorption shifts gradually from 680 to 725 nm. It is assumed that the addition of the amine converts the dimer into a monomer in which copper is bound to four monomeric carboxylic ligands and two amine molecules are located farther away in an axial position. It is of interest to note that the anion of the salt coextracted with the metal ion has no effect on the visible spectrum i.e., it is immaterial whether copper fluoride, chloride, or nitrate is extracted they all have the same spectrum. 

The formation of Cu(OH in this solution has been neglected because the Cu-EDTA complex is much more stable than the CnOH" complex and furthermore the [OH ] is much smaller than the [Y" ] over most of the pH range. 

Photodegradation of Cu-EDTA complexes Polycarbonate microchannel reactor 10 mW UV-LED (Nichia. 365 nm) [8]... 

Exercise 2 Calculate the conditional constant of the Cu -EDTA complex at pH = 13 in the absence of any buffer and of any other complexant. (We shall not take the acidic character of the complex or the formation of a binuclear complex into account.) We give K = 10 and Pi° = 10. ... 

Still another use of EDTA is in the field of art restoration. Figure C shows "before and after photographs of Rodin s bronze sculpture "The Thinker." This stood in front of the Rodin Museum in Philadelphia for about 50 years prior to its restoration in 1992. Over time the sculpture had picked up a thick coating of insoluble CuS04 3Cu(OH)2(s). Application of a wet paste containing EDTA dissolved the coating by forming the soluble Cu(EDTA) complex. 

EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu +, Co +, and Ni + at three wavelengths are summarized in the following table (all values of e are in cm )... 

This colour change can be observed with the ions of Mg, Mn, Zn, Cd, Hg, Pb, Cu, Al, Fe, Ti, Co, Ni, and the Pt metals. To maintain the pH constant (ca 10) a buffer mixture is added, and most of the above metals must be kept in solution with the aid of a weak complexing reagent such as ammonia or tartrate. The cations of Cu, Co, Ni, Al, Fe(III), Ti(IV), and certain of the Pt metals form such stable indicator complexes that the dyestuff can no longer be liberated by adding EDTA direct titration of these ions using solochrome black as indicator is therefore impracticable, and the metallic ions are said to block the indicator. However, with Cu, Co, Ni, and Al a back-titration can be carried out, for the rate of reaction of their EDTA complexes with the indicator is extremely slow and it is possible to titrate the excess of EDTA with standard zinc or magnesium ion solution. 

Reduction of CIOJ by citrate, tartrate and EDTA complexes of Fe(II) and by Cu(NH3)4 has been examined polarographically. All four reactions are first-order in reductant and C102. The data for the citrate and tartrate complexes were not reproducible but estimates of k2 (27 °C) were obtained. The rate data are... 

For instance, Cr(III) ions may coexist with Co(II) and Cu(II) ions in a complex sample. The latter two ions may produce CL emission under similar conditions as for Cr(III). Fortunately, the formation rate of the Cr-EDTA complex is relatively slower, making possible the selective determination of this metal ion in waste water [8], urine, blood, and hair [9], Owing to the small number of CL reagents explored in recent years, the elements covered by CL techniques are still rather limited. Up to now only a few elements have been found to produce direct CL emission when reacted with CL reagents. Most of the publications so far involve indirect methods for the detection of elements. 

Speciation of Pb(II) in Glatt river. The concentrations given for CO2, Pb(II), Cu(II) and [Ca2+] as well as for the pollutants EDTA and NTA are representative of concentrations encountered in this river, The speciation is calculated from the surface complex formation constants determined with the particles of the river and the stability constants of the hydroxo-, carbonate-, NTA- and EDTA-complexes.The presence of [Ca2+] and [Cu2+] is considered. 

Figure 8.7. Potential sweep function for the partial cathodic process in electroless copper deposition dissociation and reduction of Cu(II)EDTA complex. (From Ref. 31, with permission from the Electrochemical Society.)...

The lower activity of most chelate complexes than that of the aquo complex of Cu was attributed to small amounts of free Cu liberated by the labile complexes The dismutase activity reported for the [Cu(I)gCu(II)g(D-penicillamine)jjCl] complex was suppressed by EDTA or by a Chelex 100 treatment Free Cu cations can, however, not explain the very high second-order rate constant of 6x 10 M " s measured at pH 7.0 with the [Cu findomethacin) ] complex by the decay of OJ at 250 nm. With the Cu-histidine complexes, moreover, it was concluded from the influence of pH on the pseudo-first order rate constant of the dismutation of HOj/Oj that [CuHiSjH] was the active species with a second-order rate constant of 3x 10 M" s between pH 2 and 7. It was not possible kinetically to distinguish between the classical and the alternative mechanism, with respectively Cu(I) or a Cu(II)—Oj" complex as intermediate... 

Thiourea masks Cu2+ by reducing it to Cu+ and complexing the Cu+. Copper can be liberated from thiourea by oxidation with H202. Selectivity afforded by masking, demasking, and pH control allows individual components of complex mixtures of metal ions to be analyzed by EDTA titration. 

Due to the limited solubility of NTA and EDTA in their acid forms it is somewhat difficult to carry out elutions on H+ form resins. Speeding et al. [112] suggested the use of a retaining ion, which formed stable, soluble complexes with the eluant, to impregnate the resin column. They proposed Fe3+, Cu2+ and Ni2+ as retaining ions of these Cu2+ has been most widely used [115—117, 119]. Wolf and Massonne [108] used Zn2+ for the elution with NTA because the Zn(NTA) complex is more soluble than the Cu(NTA) complex. Recently Fuger [120] proposed the use of the EDTA chelate of the same ion with which the ion exchange resin is pretreated as eluant. This has been very useful in the case of radioactive tracers. 

Thus, both methods show that the reduction of the Cu(II)EDTA complex is preceded by the dissociation of the complex. 

Belal et al [40] reported on the use of flame atomic absorption spectroscopy (FAAS), coupled with ion-exchange, to determine EDTA in dosage forms. EDTA is complexed with either Ca(II) or Mg(II) at pH 10, and the excess cations retained on an ion-exchange resin. At the same time, the Ca(II) or Mg(III) EDTA complexes are eluted and determined by AAS. Calibration curves were found to be linear over the range of 4-160 and 2-32 pg/mL EDTA when using Ca(II) or Mg(II), respectively. The method could be applied to eye drops and ampoules containing pharmaceuticals. Another combined AAS flow injection system was proposed for the determination of EDTA based on its reaction with Cu(II). The calibration curve was linear over the range of 5-50 pg/mL, with a limit of detection of 0.1 pg/mL [41]. 

---