Chromatographic modes displacement

One of the three basic modes of chromatographic operation, displacement chromatography is useful for preparative separations and trace enrichment. Most liquid chromatographic methods have been performed in displacement mode. Solutes purified by displacement chromatography include metal cations, small organic molecules, antibiotics, sugars, peptides, proteins, and nucleic acids. 

Chromatographic separation of these mixtures in the elution mode is incapable of resolving many thousands of peptides present in these mixtures, even when orthogonal, two-dimensional separations are performed. The investigator is left with little option for low-abundance peptide iden-tihcation other than affinity approaches that target certain subclasses (e.g., phosphopeptides). While effective for certain applications, the latter allow for enrichment of only a small subset of low-abundance peptides. Because of its potential for broad applicability to the problem of low-abundance peptide enrichment, displacement chromatography remains a technique that offers great possibilities in this area. 

Steve Cramer (Rensselaer Polytechnic Institute) presented the next talk on the use of modeling for displacer design and comparison of the performance of chromatographic materials. He attempted to show how modeling can be employed to provide insight into the relative efficacy of various stationary phase materials for different modes of nonlinear chromatography. 

From a process-engineering point of view, there is now a better understanding of the development of concentration profiles in chromatographic columns under overloaded conditions available. This includes in particular the quantitative description of displacement and tag-along effects caused by competitive adsorption. Since it is now possible (as mentioned before) to simulate concentration profiles on a personal computer, the choice of the appropriate mode... 

The chromatographic separation of enantiomers, often referred to as enantioseparation, has received a great deal of attention in recent years. Both liquid (LC) and gas (GC) chromatographic procedures are used. The former is extremely useful for enantioseparations because of the available variations in scale, mechanism, and technique. It has been used in enantioseparations from analytical to preparative in scale, taking advantage of various modes of diastereoisomeric interactions andusing elution and displacement techniques. All the chromatographic methods involve diastereoisomeric interactions between the enantiomers of interest and... 

Chromatography may be performed as elution, frontal, or displacement. When the mode of development is not specified, a chromatographic separation is considered to be an elution. 

Chapters 7 to 9 review the closed-form solutions of the systems of Eq. 2.36 for a single component (Chapter 7) and a multicomponent mixture in elution (Chapter 8) and in the displacement mode (Chapter 9). These solutions have great importance because they describe clearly what it is that thermodynamics tries to accomplish in a chromatographic column. The imderstanding of these solutions gives precious clues to the behavior of high-concentration chromatographic bands in actual columns. 

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