Ion separation in membrane and solid phase

Izatt, Reed, M., Ion Separations in Membrane and Solid Phase Extraction Systems, 4, 225. 

Ion Separation in Membrane and Solid Phase Extraction Systems... 

Fontas, C., Antico, E., Vocanson, F., Lamartine, R., Seta, P. (2007). Efficient thiacalix [4]arenes for the extraction and separation of Au(in), Pd(n) and Pt(IV) metal ions from acidic media incorporated in membranes and solid phases. Sep. Purif. Technol., 54, 322-8. 

Liquid-liquid methods include solvent extraction with immiscible liquid-liquid systems in which a suitable ligand is dissolved in an organic phase and contacted with a metal ion containing an aqueous phase and liquid membranes. Separations can also be achieved with pseudo-phase systems such as micelles, microemulsions, and vesicles. Such separations can be solid-liquid or liquid-liquid and include separations with normal- and reversed-phase silica, and polymeric supports where the mobile phase contains the organized molecular assembly (OMA) of micelles, microemulsions, or vesicles. Separation of metal ions using the pseudo-phase systems is stiU in its infancy and a brief account will be provided here. 

Sequential injection has proven itself especially useful for a variety of separation and preconcentration schemes, It has been applied to analvtical procedures involving such methods as membrane separations, pi I adjusinienLs. solid-phase e.xiraction. precipitation, and titration. In addition to colorimetry, ion-selective elecirodes. amperometry. Huoresccncc, IR abs >rplion. chemiluminescence, and conductimeiry have been used as detection methods wi(h SlA. 

A special case of interfaces between electrolytes are those involving membranes. A membrane is a thin, ion-conducting interlayer (most often solid but sometimes also a solution in an immiscible electrolyte) separating two similar liquid phases and exhibiting selectivity (Fig. 5.1). Nonselective interlayers, interlayers uniformly permeable for all components, are called diaphragms. Completely selective membranes (i.e., membranes that are permeable for some and impermeable for other substances) are called permselective membranes. 

The unique ability of crown ethers to form stable complexes with various cations has been used to advantage in such diverse processes as isotope separations (Jepson and De Witt, 1976), the transport of ions through artificial and natural membranes (Tosteson, 1968) and the construction of ion-selective electrodes (Ryba and Petranek, 1973). On account of their lipophilic exterior, crown ether complexes are often soluble even in apolar solvents. This property has been successfully exploited in liquid-liquid and solid-liquid phase-transfer reactions. Extensive reviews deal with the synthetic aspects of the use of crown ethers as phase-transfer catalysts (Gokel and Dupont Durst, 1976 Liotta, 1978 Weber and Gokel, 1977 Starks and Liotta, 1978). Several studies have been devoted to the identification of the factors affecting the formation and stability of crown-ether complexes, and many aspects of this subject have been discussed in reviews (Christensen et al., 1971, 1974 Pedersen and Frensdorf, 1972 Izatt et al., 1973 Kappenstein, 1974). 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Until recently, samples for FIA were already extracted. Altered, centrifuged or pretreated in some way prior to assay. However, some sample preparation and preconcentration steps can now be accommodated in FIA. Some examples are on-line liquid-liquid extraction, solid phase extraction and ion-exchange procedures. In this way, FIA is managing to convert some traditionally labour-intensive steps into automated operations that have higher precision and faster throughput. FIA can also tolerate other sample types, such as fermentation broth samples and even gases through the use of silicon membrane separators and gas diffusion systems, respectively. 

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