Ion exchange function

Sykora, D., Svec, F., and Frechet, J. M. J., Separation of oligonucleotides on novel monolithic columns with ion-exchange functional surfaces, /. Chromatogr. A, 852, 297, 1999. 

Ion exchange resins based on poly(styrene-divinylbenzene) backbones display mixed mode retention mechanisms. The ion exchange functionality (sulfonic acid or carboxylic acid for cation exchangers and quartemary or primary, secondary, or tertiary amines for anion exchangers) contributes to the ionic mechanism and the backbone polymer to hydrophobic retention. This is exemplified... 

In order to increase the electroosmotic flow, a number of studies used beads with specifically designed surface chemistries that involved strong ion-exchange functionalities. The famous yet irreproducible separations of basic compounds with an efficiency of several millions of plates has been achieved with silica based... 

Monomer and polymer electrolytes containing ion-exchangeable functional groups, (I), and an ionic Uquid functional group, (II), were prepared by Best et al. (1) and used in fuel cells. 

Ion exchanger Functional group Capacity toward U (mg/g) X10- (cmVg) Reference... 

In Chapter 8, Zuyi Tao, in order to provide a better understanding of the ion-exchange behavior of amino acids, has compiled their particular acid-base properties, their solubility in water, their partial molal volumes, and their molal activity coefficients in water at 25 C. This information has been used in Gibbs-Donnan-based equations to facilitate a better understanding of the mechanism of amino acid uptake by ion exchangers at low and high solution concentration levels. Measurement of distribution coefficients and separation factors are also described. The eventual resolution of thermodynamic ion-exchange functions (AG, AH, and AS) is provided for the reader. 

Ion-exchange chromatography is a very predictable technique because the mechanism is well defined. The capacity factor (k) for the binding of an ionic solute to an ion-exchange functional group in lEC is directly related to the concentration (c) of salt in the mobile phase ... 

Explanations to abbreviations derived from trivial terms for ion exchange functional groups (1) Sulfo-, sulfomethyl-, sulfoethyl-, sulfopropyl-, sulfobutyl- (2) Phosphonic- (3) Carboxyl-, carboxy-methyl- (4) Trimethylaminomethyl-, Triethylaminoethyl- (5) Hydroxyethyidimethylaminomethyl- ... 

The term homogeneous is used loosely to describe membranes that are not classified as heterogeneous. On a molecular scale no membrane is truly homogeneous, because the unlike parts of the polymer, hydrophihc ion-exchange functional groups and hydrophobic hydrocarbon chains, tend to become segregated into clusters that are much smaller than the dimensions of the resin particles in the heterogeneous membranes. 

Typical homogeneous membranes have a polymer matrix of styrene cross-linked with divinylbenzene (DVB) and ion-exchange functional groups of sulfonic acid or quaternary amines. Manufacture of DVB yields an impure product containing nearly 50% of ethylstyrene, which participates in the polymerization but does not accept functional groups readily. In some cases the film of styrene-DVB copolymer is made in one step, and the functional groups are added in subsequent steps. 

Ion-permeable membranes are also made by swelling existing films with styrene and DVB, which can then be post-treated to add functional groups, or by grafting of ion-exchange functional groups directly onto the polymer matrix of existing films. For example, free radicals formed by radiation of polyethylene or fluoropolymer films become sites for addition of vinyl sulfonic acid, acrylic acid or vinyl amines [30]. 

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