Hydrophilic Polymer Stationary Phases

Hydrophilic polymer sorbents are mainly based on natural polymers, for example, agarose and polymethacrylates. Some newly developed phases use poly-vinylethers or hydrophilized poly-styrene/divinylbenzenze copolymers. These materials vdll be discussed in the form of their functionalized products. Nevertheless, some of the 

The advantages of ion-exchange chromatography are its straightforward adsorption principle that is based on the Coulomb interaction that can be adjusted according to the isoelectric point (pl) of the proteins to be separated. The binding mechanism can be tuned over a wide area of conditions by choosing different types 

1 Optimization of Ion-Exchange Resins To optimize an ion-exchange sorbent several options have to be taken into account  

Resin Manufacturer Base matrix/surface modification Particle size [pm] 

Eshmuno S Merck Poly-vinyl derivative/tentacle 75-95 

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PNIPAM and its copolymers are not the only options for thermoresponsive stationary HPLC phases. Poly(acrylates) and poly(methacrylates) bearing OEG groups in the side chains are known as thermoresponsive polymers that offer some advantages over PNIPAM [40]. Such polymers were recently employed for the modification of silica monoliths, which then served as stationary phase in the HPLC separation of steroids [193], Unsurprisingly, the results were qualitatively similar to those obtained for PNIPAM-based systems, but the separation of relatively hydrophilic steroids was superior. 

A few synthetic helical polymers are known to act as chiral selectors, and are widely used as chiral stationary phases (CSP) in gas or liquid chromatography [88,89]. Recently, it has been reported that the preference of one helical sense in isotropic solution can be induced by some interaction between optically inactive polymers and chiral solvents/additives. Examples of this include poly(n-hexyl isocyanate) [17,18] and poly(phenylacetylene)s bearing functional groups [20,27]. The polysilane derivatives also show chiral recognition ability in solution at room temperature. Poly(methyl-/ -pinanylsilane) which includes two chiral centers per bulky hydrophobic pinanyl side group [60] exhibits an enantio-recognition ability for hydrophobic -pinene, but none for hydrophilic methanol. 

Gels used for the stationary phase can be hydrophilic, for separations in aqueous and other polar solvents, or hydrophobic, for use in non-polar or weakly-polar solvents. Agar, starch, polyacrylamide and cross-linked dextrans possess hydroxyl or amide groups and are thus hydrophilic. They swell in aqueous media and in such solvents as ethylene glycol and dimethylform-amide. Bio-Cel (a co-polymer of acrylamide and jV.W -methylene-bisacryl-amide) and Sephadex (dextran cross-linked with epichlorhydrin) arc two commercially available gels made in bead form. Cross-linking produces a... 

Supports for SEC of proteins are designed to be neutral and very hydrophilic to avoid disruption of protein structure and interaction of the solutes with the support by ionic or hydrophobic mechanisms. The base matrix can be either silica or polymer efforts are made to totally mask its properties with a carbohydratelike stationary phase. The pore structure is critical to successful SEC. Not only must the total pore volume (F,) be adequate for separation, the pore diameter must be consistent and nearly homogeneous for attainment of maximum resolution between molecules with relatively small differences in molecular size (radius of gyration or molecular weight). A twofold difference in size is usually required for separation by SEC. Pore homogeneity can be assessed from the slope of the calibration curve of the logarithm of the molecular weight versus the retention time or the partition coefficient (Kd) = (F - Fq)/F , where F is... 

Materials with inorganic or porous hydrophobic or (less frequently) hydrophilic organic polymer matrices and graphitized carbon are stable over a broad pH range from 0 to 12-14 hence, they are useful for separations of basic compounds. RP phases on aluminium and zirconium oxide supports exhibit hardness and mass transfer properties comparable to silica, and can be prepared by forming a cross-linked polystyrene, polybutadiene, or alkylated polymethylsiloxane layer on the support surface to which alkyls are attached. The inorganic surface, encapsulated by a nonpolar stationary phase, does not come into contact with the mobile phase or with the analyte, so these materials can be used in the pH range 1-14. 

There is a great selection of stationary phases for HILIC silica, derivatized silica with diol, nitrile, amino or amide groups, silica with a hydrophilic polymeric coating, and various polymers. They all were especially developed for HILIC whereas... 

In general, one can divide size exclusion chromatography into two categories SEC in organic solvents and SEC in aqueous solvents. For polymers that are soluble in organic solvents, styrene-divinylbenzene stationary phases are used for the most part. For packings that are soluble in aqueous eluents, -hydrophilic methacrylates are most commonly used. 

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