Ion Exchange Matrix

These materials can be broadly categorized into those which are totally inorganic in nature and those that are synthetic organic resins. 

Inorganic ion exchangers include both naturally occurring materials such as mineral zeolites (sodalite and clinoptilolite), the greensands, and clays (themontmorillonite group) and synthetic materials such as gel zeolites, the hydrous oxides of polyvalent metal (hydrated zirconium oxide) and the insoluble salts of polybasic acids with polyvalent metals (zirconium phosphate). 

The synthetic organic resins consist of cross-linked polymer matrix which is functionalized to provide their ion exchange capacity. The matrix usually must undergo additional reactions to provide the strong acid cation, strong base anion, weak acid cation or weak base anion functionality. 

Resins with cellulosic matrices are much more hydrophilic and these do not tend to denature proteins. Cellulosic resins have been used extensively in the laboratory analyses of biological materials, enzyme immobilizations and small scale preparations. The low capacity and poor flow characteristics have limited the usefulness of these matrices for larger applications. 

Recently, diethylaminoethyl (DEAE) silica gel was shown to be an improvement over typical cellulosic-matrices resins for the separation of acidic and neutral lipids from complex ganglioside mixtures. The specific advantages claimed were  

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Conduction in the raw doped polymer can be improved by devices such as compression and stretching and judicious after-synthesis dopant ion exchange. Matrix-guided electropolymerization also yields superior products. 

In this respect the dense nonporous ion-exchange material of a membrane may be viewed as a one-phase medium. In contrast to this a porous bulk ion-exchanger (e.g., an ion-exchange bed or a single microporous ion-exchange bead) is a two-phase medium with the possibility for each ion to be in either one of the two phases—in the ion-exchange matrix proper or in the aqueous pore. 

Salts can affect sorption of organic compounds by displacing cations from the soil ion exchange matrix, by changing the activity of the sorbate in solution, and by changing the charge density associated with the soil sorption surface (Hamaker and Thompson, 1972). Salt effects are most important for basic sorbates in the cation state, where an increase in salinity can significantly lower the sorption coefficient. Salt effects are least important for neutral compounds, which may show either increases or decreases in sorption as salinity increases. 

In general, an ion-exchange matrix will require regeneration and swelling before use according to the manufacturer s instructions (jecMethod), although DEAE-Sephacel and DEAE-Sepharose CL-OB are supplied preswollen and ready to use. 

At times, the effect of separation by charge and by mass is combined in the same column with the use of a biphasic matrix the distal half of the column is filled with HPLC resin for separation based on the mass of proteins, and the proximal half of the column is packed with ion exchange matrix separating the proteins based on the charge. This biphasic column is used when the elution buffer for the two systems is the same or compatible. Such separation by a biphasic column is suitable for the multidimensional protein identification technology (mudPIT) by mass spectroscopy. 

Zr(0H)As04,xH20, which may be useful as an ion-exchange matrix, has been obtained by heating arsenious acid, zirconium(iv) oxychloride, and potassium persulphate in aqueous HCl. ... 

A relatively recent approach in CIC involves more efficient, small particle size substrates as the chelating surface. The use of these high-performance stationary phases means that reasonably fast analytical separations of groups of metal ions can be obtained similar to conventional high-performance ion-exchange. Matrix isolation is not normally required as the chelating column is relatively insensitive to concentrated salt solutions. Preconcentration, if necessary, can also... 

We have been able to purify heat shock activator protein, a 110 kD polypeptide, to over 95% homogeneity from a 0.35 M NaCl nuclear extract prepared from heat shocked Drosophila tissue culture cells (3). The extract was chromatographed on heparin-Sepharose, twice sequentially on specific DNA-Sepharose (4 ml and 0.6 ml bed volumes), and on FPLC Mono S (a Pharmacia ion exchange matrix). A typical purification requires 1.5 x 10 cells from which several micrograms of homogenous heat shock activator protein are obtained. The yield at the affinity step is > 50%. Typical overall yields range between 10% and 20%. The... 

In operation, metal ions (M ) in solution are preferentially bound to the insoluble matrix with the concomitant release of protons or another cation (M). The toxic metal ion (M ) is effectively held within the matrix. The most common examples of cation exchange are water-softening resins. Hard water (containing Ca ) can be treated with an ion-exchange matrix containing sodium ions. The sodium ions are exchanged with the calcium ions, with the resultant removal of calcium from solution (see Figure 14.3). 

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