Ionogenic exchangers

It has been shown that the effects found are caused by specific solvation of both the PhAA ionogenic and other polar groups by the plasticizers used, as well as by the influence of ion-exchangers nature on the PhAA cations-anionic sites complex formation constants. 

There are some cases where a reaction, that is, the formation or dissolution of a chemical bond, is involved along with ion exchange phenomena (Helfferich, 1983). Examples of this are acid-base neutralization, dissociation of weak electrolytes in solution or weak ionogenic groups in ion exchangers, complex formation, or combinations of these (Table 5.2). With some of these, very low apparent D in ion exchangers have been noted. 

The drawbacks of ionic suppression and ion exchange chromatography led to the development of ion-pair chromatography (IRC)—an intriguing mode of HPLC that allows the separation of complex mixtures of polar, ionic, and ionogenic species. IPC is now an established and valuable separation strategy. 

FIGURE 34.5 Conceptualized distribution of ionogenic groups within cation-exchange membranes for (a) homogeneous membrane and (b) heterogeneous membrane. 

It is the aforesaid methods that are most generally used to prepare the cross-linked network. It is this network that carries the ionogenic centres, designated as the functional groups of the resins, which give the ion-exchangers their typical... 

The process of exchange of ions taking place at the ionogenic site of the ion-exchanger which has been mentioned above is a reversible process and can be expressed by the equation (R = ion-exchanger) ... 

If one or more of the ions in an ion-exchange column is the conjugate acid or base of a weak base or weak acid, the pH of the solution will have an important effect on the degree of dissociation of the weak acid or base. Since it is ions that are retained on ion-exchange columns and since the pH of the solution can affect the relative number of ions in the column because of the dependence of the dissociation constant (or, in other words, pK values) of the ionogenic group on pH, the pH can have a large effect on the retention of the species on the column. 

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