EDTA-calcium complex

Discussion. When calcium ions are titrated with EDTA a relatively stable calcium complex is formed ... 

Dosages of EDTA are delivered as the calcium disodium salt, Na2[Ca(EDTA)]. The calcium complex prevents EDTA from extracting iron from the blood. Unlike iron, heavy metal ions such as preferentially... 

As with (105), ligand (106, dota) also forms strong complexes with a range of both non-transition and transition metal ions (Stetter Frank, 1976 Delgado da Silva, 1982 Spirlet, Rebizant, Desreux Loncin, 1984) which are often more stable than the corresponding edta complexes. In particular, the calcium complex shows extremely high stability and very stable complexes are also formed with the trivalent lanthanides (Desreux, 1980 Spirlet, Rebizant, Desreux Loncin, 1984). 

Ion-X SA, conditioned with EDTA 0.005M EDTA, 0.05M NaCl in water-methanol, 95 5 and 70 30 37 5 nm TC in urine extracts as calcium complex 183... 

Large Unilamellar Vesicles from Cochleates Large unilamellar vesicles can be produced with the cochleate approach [139], Small unilamellar vesicles consisted from phosphatidylserine adopt a cochleate shape after addition of calcium. Addition of EDTA creates complexes with calcium, turning the cochleates to LUVs. 

FIGURE 2.13 The equivalent fractions of manganese(II) (XMn), calcium (XCa), hydrogen (XH), sodium ions (XNa), and their sum (X total) in the interlayer space of montmorillonite as a function of pH of the solution. The ratio of the total concentrations of EDTA, calcium, and manganese ions is 1 1 1. The equivalent fractions of calcium and hydrogen ions as a function of pH without the complex-forming agent is also shown. 

Curve A in Figure 17-6 is a plot of data for the titration in Example 17-4. Curve B is the titration curve for a solution of magnesium ion under identical conditions. The formation constant for the EDTA complex of magnesium is smaller than that of the calcium complex, which results in a smaller change in the p-function in the equivalence-point region. 

Superior foaming properties of milk have been obtained by addition of calcium complexing agents. Kelly and Burgess (1978) demonstrated that addition of sodium hexametaphosphate to milk protein concentrate solutions prepared by ultrafiltration improved foam volume and stability on whipping. The addition of EDTA to milk, which causes dissociation of the casein micelle, improved the foaming properties of milk (Ward et al., 1997). 

When calcium ions are titrated with EDTA a relatively stable calcium complex is formed Ca2+ + H2Y2----------------------> CaY2- + 2H ... 

The titration of calcium only in the presence of magnesium is carried out at a pH of 12, conditions under which the magnesium is converted to magnesium hydroxide, precipitates, and is rendered unreactive toward EDTA. Calcein, the indicator used in this titration, itself forms a nondissociated ion with calcium, which is yellow-green. In the alkaline solution, the indicator itself is brown. At the endpoint in the titration, the calcium is extracted from the Calcein-calcium complex by the EDTA and the color changes from yellow-green to brown. Magnesium does not form a nondissociated ion with the indicator. 

Practical considerations call for a liquid of high viscosity and low vapour pressure and a low solubility in water. A solution of a calcium complex with a dialkylphosphoric acid (e.g. ((RO)2POO)2Ca, where R = CgH to C16H33) in a very polar solvent such as di-n-octylphenyl phosphate can be used in an ion-selective electrode that gives a linear response over 10 [Ca +] 5 X 10. Solutions of Ni(phen)3 nitrate (or perchlorate, or tetrafluoroborate) in nitrobenzene of p-nitrocymene have been used as specific ion electrodes for nitrate (or perchlorate, or tetrafluoroborate). A mercury dithizonate electrode can be prepared which is ion-specific for mercury (II) and replaces the mercury drop electrode for the titration of Al, Ca, Cu, Hg , Ni and Zn with EDTA. Silver, lead and palladium dithizonates have also been used in titrimetry. ... 

Chelating agents, like all chemical compounds, exhibit toxic effects. These can arise from the fact that they increase the excretion of essential trace elements or from more subtle interactions. Thus all compounds which contain sulfhydryl compounds are capable of causing allergic reactions, such as the skin rash reported for DMSA (Grandjean et al. 1991), or the numerous problems which may arise from the continued administration of d-penicillamine such as nephrotic syndrome and anuria (Dubois et al. 1990). The administration of EDTA by itself may result in tetany due to the rapid drop in serum calcium which results, this being the reason for its customary administration as the calcium complex. 

We studied the calcium—EDTA chelation using Calcein [4] as the fluorescent indicator. This indicator forms a fluorescent complex with free calcium ions. In order to determine calcium in a sample, the excess EDTA remaining after stoichiometric chelation of calcium in the sample is "back-titrated" with a known concentration of calcium solution. The equivalence point is reached when all of the excess EDTA is chelated and is detected by fluorescence of the Calcein-calcium complex formed by a slight excess of free calcium ions. The calcium content of the sample (in micrograms) is equal to the volume (in milliliters) of titrant added when no sample was introduced, minus the volume (in milliliters) of titrant added when the sample was introduced, times the calcium content of the titrant (in micrograms per milliliter). 

Chemical interferences The only example of any consequence pertains to the measurement of calcium. The ion forms a refractory phosphate molecule and atomization is thereby impaired. Diluents containing La + or Sr +, preferentially bind to the phosphate and release the Ca +, or EDTA to complex the Ca + in solution allowing its release in the flame, effectively eliminate this interference. An alternative strategy is to use the hotter nitrous oxide-acetylene flame. A few other chemical interferences have been recorded in atypical settings and are not relevant to biomedical samples. 

Ethylenediamine tetraacetic acid (EDTA) [60-00-4] (Sequestrene), an anticoagulent at 1 mg of the disodium salt per mL blood, complexes with and removes calcium, Ca ", from the blood. Oxalate, citrate, and fluoride ions form insoluble salts with Ca " and chelate calcium from the blood. Salts containing these anticoagulants include lithium oxalate [553-91-3] 1 mg/mL blood sodium oxalate [62-76-0]2 mg/mL blood ... 

Calcium is essential to several steps in the enzyme cascade of the blood clotting process, such as the conversion of prothrombin to thrombin (23). Clotting can be inhibited in stored blood suppHes by addition of complexing agents such as EDTA or citrate which reduce the levels of the free ion, Ca(Il). 

EDTA forms 1 1 complexes with a large number of cations, including those of some of the main-group metals. The complex formed by calcium with EDTA is used to treat lead poisoning. When a... 

---