Resins crown ether modified

A group of the methods for pre-concentration of traces includes the extraction of metals by the resins modified with organic reagents, e.g., 8-hydroxyquinoline, DDTK [58], Bromopyrogallol Red [59], Zincon [60], and crown ethers [61]. Reviews of the methods have been presented [62,63]. 

Pb was sorbed on a resin [27] and polyurethane foam [28] modified with the crown ether, 18-crown-6, and its derivatives. The sorption of Pb (and other metals) on a chelating resin containing Arsenazo I was studied in water-organic solvent media [29]. A silica gel, modified with 2-mercaptobenzothiazole [30] or 2-mercaptobenzimidazole [31 ] was used for concentration of Pb and other heavy metals from aqueous solutions. Pb was selectively separated from Al, Mg, and Fe(III) on a cation exchanger modified with tin(IV) antimonate [32]. 

Crown ethers have been immobilized within polymer supports and used in metal ion separation, Crown ether moieties at cross-linked polystyrene have been prepared by the reaction of cross-linked chloromethylated polystyrene with hydroxyl-substituted crown ethers [52], The resins 15 formed from the condensation of dibenzo—18-crown-6 and formaldehyde were modified with phosphonate monoethylester and phosphonic acid groups [53]. Resin 15 demonstrates selectivity for K(I) over the other alkali metal ions at pH < 8, and selectivity for Li(I) at pH > 8. A resin 16 prepared from the condensation of a substituted crown ether with formaldehyde is selective for Na(I) over the other alkali metal ions [54],... 

Another application of copolymerization technology is the synthesis of resins containing crown ether units to give materials with extraction and re-extraction properties. These resins are synthesized from phenol or 1,3-benzenediol, methanal, and benzo-13-crown-4 and benzo-9-crown-3 (Scheme 24). These crown ether containing resins show otential applications in catalysis because of easy recovery of the resin beads by filtration and the prevention of contamination of the catalyzed product with toxic macrocycles. Furthermore, these modified phenolics may be applicable in analytic chemistry as chromatographic stationary phases for separation of ionic substances from neutral ones and in heterogeneous phase-transfer catalysis in preparative chemistry [162],... 

Inorganic and organic anions can also be separated on cross-hnked polymers modified with cyclic ethers. Pioneering work in the field of adsorbing crown ethers onto chemically bonded reversed phases and PS-DVB polymers has been carried out by Kimura et al. The number of applicable crown ethers is limited because of their limited solubility and high price. Moreover, crown ether resins are mechanically unstable and are therefore operated with low flow rates, thus resulting in long analysis times. 

Polymeric crown ether resins are mechanically unstable and are, therefore, operated with low flow rates between 0.05 and 0.1 mL/min resulting in long analysis times. Typical for all polymeric crown ether phases is the relatively low chromatographic efficiency, which does not meet today s requirements. However, this problem can be overcome by immobilizing crown ether polymers on the surface of a solid support. Modified and non-modified silica are predominantly used as support materials. Igawa et al., for instance, coated silica particles with the above-mentioned polyamide crown ether resin and obtained significantly better separations then with the rmcoated resin. 

Molybdenum and tungsten have been separated on a chelating resin with thioglycolate groups. A mixture of these metals is sorbed from an acetate solution of pH 4.3, then Mo and W are eluted successively with 2 M HCl and a mixture of 0.1 M NaOH and 0.1 M NaCl [36]. The sorption of Mo and W on silicate sorbents, modified with hydroxamic acids, was also studied [37,38]. Mo was also preconcentrated on dibenzo-18-crown-6 ether columns from HCl [39] and HBr [40] media. 

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