Chromatographic separation, modes exclusion chromatography

It is important for the analyst to be able to select the best stationary phase to use for a particular chromatographic analysis. Silica gel can be used in two modes of chromatographic separations as a stationary phase in normal elution development or as a stationary phase in exclusion chromatography. 

Such precise control of porous properties is expected to be very useful in the design of specialized CEC columns for separation in modes other than reversed-phase. For example, size exclusion chromatography (SEC) is an isocratic separation method that relies on differences in the hydrodynamic volumes of the analytes. Because all solute-stationary phase interactions must be avoided in SEC, solvents such as pure tetrahydrofuran are often used as the mobile phase for the analysis of synthetic polymers, since they dissolve a wide range of structures and minimize interactions with the chromatographic medium. Despite the reported use of entirely non-aqueous eluents in both electrophoresis and CEC [65], no appreciable flow through the methacrylate-based monoliths was observed using pure tetrahydrofuran as the mobile phase. However, a mixture of 2% water and tetrahydrofuran was found to substan-... 

Oddly, IPC was also performed on a classical ion exchange colnmn to separate 17 anionic, neutral, and cationic arsenic species in a single chromatographic run, thanks to a multiplicity of retention modes on this packing material [39], Ion pairing proved also valuable in size exclusion chromatography of sulfonated lignins [40],... 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

The concept of combining ion-exclusion and ion-exchange chromatography was introduced by Rich et al. [10]. It serves to improve the selectivity of the chromatographic separation of inorganic and organic acids in complex matrices. Its mode of action is schematically depicted in Fig. 4-11. 

In a more general sense, the size exclusion mode of liquid chromatography relates to a separation regime, where entropic interactions are predominant and TAS > AH. In the reverse case, AH > TAS, separation is mainly directed by enthalpic interactions. As both separation modes in the general case are affected by the macromolecule size and the pore size, a certain energy of interaction may be introduced, characterizing the specific interactions of the monomer unit of the macromolecule and the stationary phase, e is a function of the chemical composition of the monomer unit, the composition of the mobile phase of the chromatographic system, and the temperature. 

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