Aluminum-EDTA chelate

Masking can be achieved by precipitation, complex formation, oxidation-reduction, and kinetically. A combination of these techniques may be employed. For example, Cu " can be masked by reduction to Cu(I) with ascorbic acid and by complexation with I . Lead can be precipitated with sulfate when bismuth is to be titrated. Most masking is accomplished by selectively forming a stable, soluble complex. Hydroxide ion complexes aluminum ion [Al(OH)4 or AlOa"] so calcium can be titrated. Fluoride masks Sn(IV) in the titration of Sn(II). Ammonia complexes copper so it cannot be titrated with EDTA using murexide indicator. Metals can be titrated in the presence of Cr(III) because its EDTA chelate, although very stable, forms only slowly. 

Reaction with chelating agents. Such reactions have been used primarily for partial dealumination of Y zeolites. In 1968, Kerr (8,21) reported the preparation of aluminum-deficient Y zeolites by extraction of aluminum from the framework with EDTA. Using this method, up to about 50 percent of the aluminum atoms was removed from the zeolite in the form of a water soluble chelate, without any appreciable loss in zeolite crystallinity. Later work (22) has shown that about 80 percent of framework aluminum can be removed with EDTA, while the zeolite maintains about 60 to 70 percent of its initial crystallinity. Beaumont and Barthomeuf (23-25) used acetylacetone and several amino-acid-derived chelating agents for the extraction of aluminum from Y zeolites. Dealumination of Y zeolites with tartaric acid has also been reported (26). A mechanism for the removal of framework aluminum by EDTA has been proposed by Kerr (8). It involves the hydrolysis of Si-O-Al bonds, similar to the scheme in Figure 1A, followed by formation of a soluble chelate between cationic, non-framework aluminum and EDTA. 

Aluminum-deficient Y zeolites prepared by partial removal of aluminum with a chelating agent (e.g. EDTA) also show improved thermal and hydrothermal stability compared to the parent zeolite. The optimum stability was found in the range of 25 to 50 percent of framework A1 extraction (8). However, the maximum degree of dealumination is also affected by the SiO /Al O ratio in the parent zeolite a higher ratio appears to allow more advanced dealumination without loss of crystallinity (8,25,45). Above 50 or 60 percent dealumination, significant loss of crystallinity was observed. Calcination of the aluminum-deficient zeolite resulted in a material with a smaller unit cell size and lower ion-exchange capacity compared to the parent zeolite. 

Virtually all chelate complexes of the type M(Ox)m derived from the cation Mm+ are extractable into chloroform and, being coloured, form the basis of spectrophotometric determinations. The extractions can be made more selective by controlling the pH (cf. Section 10.2.2.1) and/or by using suitable masking agents. Thus extraction of the yellow aluminum trisoxinate can be made almost specific at pH 8.5—9.0 if EDTA, cyanide ions and sulfite ions (to reduce FeI I to Fe11) are present. Since the range for extraction of individual metal oxinates extends from pH 1.6 to 14, separation of individual species is facilitated.52 59... 

The addition of a chelator to peritoneal dialysate was also reportedly successful in augmenting the clearance of heavy metals in PD. In particular, arsenic clearance with DMSA [60], lead clearance with EDTA [61], and aluminum clearance with DFO [62] have been reported. 

Sanders et al. (1983) have also shown that the effects of Cu(II) on the growth of crab larvae and on their metallothionein with copper chelate buffer systems must be interpreted on the basis of free Cu ion activity. The data obtained reveal predictable relations between [Cu ] in seawater and processes at the cellular and organismic levels. Similarly, the uptake of metal ions by plants (e.g., of aluminum) is usually related to free metal-ion activity. Others have shown that the chelation of a variety of metals reduces the toxicity of metals to organisms for example, a reduction in the uptake of mercury by fish in the presence of EDTA and cysteine a reduction in copper and/or zinc toxicity to... 

Plutonium-239 DTPA (see p 439) chelator. Dose 1 g in 250 mLD5W IV over 30-60 min daily. Wounds Irrigate with 1 g DTPA in 250 mL water. EDTA (see p 440) may also be effective if DTPA is not immediately available. Aluminum-containing antacids may bind plutonium in Gl tract. 

Two chelating agents, ethylenediaminetetraacetic acid (EDTA) and 8-hydroxyquinoline, also have been used for calcium and magnesium determinations. They are effective in controlling a number of interfering ions, including phosphate, sulfate, aluminum, silicon, boron, and selenium. 

Chelating agents also are effective in certain cases. Ethylenediaminetetra-acetic acid (EDTA) forms strong chelates with alkaline earth elements and can be used to protect magnesium and calcium from reaction with phosphate, sulfate, selenium, boron, aluminum, and silicon. 8-Hydroxyquinoline has been used to protect magnesium and calcium from aluminum. 

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