Special ion exchange materials

The vast majority of applications and theoretical treatments of ion exchange are concerned with the established copolymer materials previously described. However, an introduction to resin exchangers would be incomplete without a brief reference to some other more specialized products. 

It is important to realize that specificity does not necessarily mean an affinity by the exchanger for one ion only, and in many ways the term specific can be misleading. Selective or chelating ion exchange is a better description since commonly the relative affinities of the resin for several ions, not just one ion, are enhanced compared with 

It is equally important to appreciate that a high selectivity for a particular ion does not necessarily mean that the resin concerned is bound to have immediate commercial application. The reason for this is that the property of high affinity is always associated with a reduction in the degree of reversibility in cyclic operations thereby rendering regeneration difficult. 

Tailored copolymer resins are not the only exchangers to exhibit specific affinities towards selected ions. Many types of inorganic materials such as clays, zeolites, amphoteric oxides, heteropolyacid salts, and phosphates exhibit useful specificity towards selected monovalent and polyvalent ions. In the laboratory such media are often the basis of chromatographic separations, whilst industrially many such materials offer benefits in radioactive waste effluent treatment for removing nucleides such as caesium ( Cs) and strontium ( °Sr). 

An ion exchange reaction is usually considered as taking place between a solid and a liquid phase. A degree of flexibility in this definition is required in order to accommodate the various organic liquid ion exchangers which have found important application over the last 40 years, especially in the field of extraction metallurgy. The 

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As a special ion exchange material, amphoteric ion exchange resin has unique separation functions. A snake-cage resin consists of a strongly alkaline anionic exchange resin with a linear poly(acrylic acid) (see Fig. 6). 

Ion exchange materials are a special class of polyelectrolytes. The chemical and physical properties of an ion exchange material play a more important role in determining its suitability for a biochemical application than for other types of applications. The chemical properties to be considered are the matrix and the ionic functionality attached to the matrix. The important physical properties are the pore size, the pore volume, the surface area, the density and the particle size. A list of commercial producers of granular or bead ion exchange materials is given in Table 8. 

The older classic low speed LPLC methods are often used for biochemical separations, because they are very simple, modest in instrumentation, and therefore cheap. They can be realized in every laboratory without special equipment. Also, ion exchange materials for these purposes need not be so finely and carefully prepared nor stand high pressure, and are usually inexpensive. The most important materials... 

Hoffpauir and Guthrie (102) have proposed a unique method for the isolation of proteins low in ash and phosphorus contents and for the purification of protein preparations. They used anion exchange materials to increase the pH of aqueous suspensions of peanut meal and cation exchange materials to reduce the pH of the protein dispersion to the isoelectric range. The use of specially prepared aminized and phosphoryl-ated cotton fabrics as ion exchange materials has made the method practical. 

Europium oxide is now widely used as a phospor activator and europium-activated yttrium vanadate is in commercial use as the red phosphor in color TV tubes. Europium-doped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years. 

The major chemical problem met in ion-exchange practice is the fouling or poisoning of the anion resins by organic matter. The various counter measures deployed include pre-flocculation, oxidation of the organic material, the use of specially developed resins, and treatment of the fouled resins by brine and/or hypochlorite. 

Membranes are highly viscous, plastic structures. Plasma membranes form closed compartments around cellular protoplasm to separate one cell from another and thus permit cellular individuality. The plasma membrane has selective permeabilities and acts as a barrier, thereby maintaining differences in composition between the inside and outside of the cell. The selective permeabilities are provided mainly by channels and pumps for ions and substrates. The plasma membrane also exchanges material with the extracellular environment by exocytosis and endocytosis, and there are special areas of membrane strucmre—the gap junctions— through which adjacent cells exchange material. In addition, the plasma membrane plays key roles in cellcell interactions and in transmembrane signaling. 

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