Nature of ion-exchangers

52 (pre-swollen, DEAE-substituted Whatman) is a widely used mi-crogranular cellulose which consists of dense rod-like particles. High flow rates can be obtained with the recently developed bead-like particles, such as DEAE-Sephacel (Pharmacia) and DEAE-Servacel (Serva). Other, less frequently used anion-exchangers are DEAE-Sepharose CL-6B, DEAE-Sephadex A-50 and QAE-Sephadex A-50. Cationic exchangers are considerably less used than the basic exchangers for the purification of Ig. 

In all these procedures, the choice and careful preparation of buffers are important. Cationic buffers, (Tris, imidazole, ethylenedi-amine, etc.) should be used with DEAE- and QAE-exchangers. Since such buffers carry the same charge as the ion-exchanger, they are not bound and will not cause local disturbances in pH or take part in the exchange process. Many examples exist in immunochem-istry where good results were obtained without following this rule (e.g., phosphate buffer with DEAE-exchangers). 

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Despite the intrinsically nonspecific nature of ion-exchange and reversed-phase/hydrophobic interactions, it is often found that chromatographic techniques based on these interactions can exhibit remarkable resolution this is attributed to the dynamics of multisite interactions being different for proteins having differing surface distributions of hydrophobic and/or ionizable groups. 

Nature of ion exchange resin. The absorption of ions will depend upon the nature of the functional groups in the resin. It will also depend upon the degree of cross-linking as the degree of cross-linking is increased, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially. 

Within one type of zeolite, adsorption, chromatographic, catalytic, and other properties are determined to a certain extent by the nature of ion exchange cations, by their number per unit cell, by the degree of population of single centers (positions) in the crystal framework, and by other things. 

Origin and Nature of Ion Exchange Behaviour in Molecular Sieves... 

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