Applications of Displacement Chromatography

Frontal Analysis, Displacement and the Equilibrium-Dispersive Model 

Pr = Proteins, AA = Amino acides, PAA = Protected Amino acids, O = Organic, R = Rare Earth, L = Light metals, NA = Nucleic Acids, P = Peptides, S = Sugars. 

---

The first part of the chapter deals with the problems which arise from the use of actual columns, having a finite efficiency. The rest of the chapter is devoted to a discussion of the practical problems encoimtered in developing a separation by displacement chromatography, and to a brief review of the applications of displacement chromatography. 

Tswett recognized the difference between elution and displacement development, although Tiselius was the first to clearly define these differences. While displacement was popular in the 1940s, that popularity waned in the 1950s. In the 1980s, there was a resiugence of interest in displacement operation due to the efficient utilization of the stationary phase possible in that mode. Frenz and Horvath have pubhshed a comprehensive review of the history and applications of displacement chromatography. 

Further progress can be expected since new column materials (e.g., monolithic columns) and further improved FIPLC systems (e.g., ultra performance systems) have been developed to speed up analytical runs significantly. Their use as routine on-line detection tools will improve the productivity of preparative FIPLC not only in applications where broad overloaded peaks are observed, but also in cases where high concentrations of different solutes elute close to each other, an inherent aspect of displacement chromatography systems for example. 

G. Application of displacement thin-layer chromatography to toad-poison bufadienolides. J. Planar Chromatogr. 1999, 12, 120-123. 

Chapters 10 to 13 review the solutions of the equilibrium-dispersive model for a single component (Chapter 10), and multicomponent mixtures in elution (Chapter 11) and in displacement (Chapter 12) chromatography and discuss the problems of system peaks (Chapter 13). These solutions are of great practical importance because they provide realistic models of band profiles in practically all the applications of preparative chromatography. Mass transfer across the packing materials currently available (which are made of very fine particles) is fast. The contribution of mass transfer resistance to band broadening and smoothing is small compared to the effect of thermodynamics and can be properly accounted for by the use of an apparent dispersion coefficient independent of concentration (Chapter 10). 

The application of the z-transform and of the coherence theory to the study of displacement chromatography were initially presented by Helfferich [35] and later described in detail by Helfferich and Klein [9]. These methods were used by Frenz and Horvath [14]. The coherence theory assumes local equilibrium between the mobile and the stationary phase gleets the influence of the mass transfer resistances and of axial dispersion (i.e., it uses the ideal model) and assumes also that the separation factors for all successive pairs of components of the system are constant. With these assumptions and using a nonlinear transform of the variables, the so-called li-transform, it is possible to derive a simple set of algebraic equations through which the displacement process can be described. In these critical publications, Helfferich [9,35] and Frenz and Horvath [14] used a convention that is opposite to ours regarding the definition of the elution order of the feed components. In this section as in the corresponding subsection of Chapter 4, we will assume with them that the most retained solute (i.e., the displacer) is component 1 and that component n is the least retained feed component, so that... 

However, it is possible to modify almost any adsorbent so as to give linear isotherms (Chapter 4). so that this theoretical advantage of displacement over elution is of academic interest only. A quite specialized form of displacement chromatography, with fluorescent indicators added to the sample so as to mark band boundaries on the column 37), is still widely used in the petroleum industry for the routine analysis of gasolines. The extension of this technique to other sample types has been discussed 38) but has so far found no reported applications. 

An additional problem exists in which impurities in the displacer itself complicate separation.54 Also, the displacer itself must be removed from the column, which lengthens regeneration time and can adversely affect throughput. Ironically, while the difficulties involved in identifying displacers and in column regeneration have retarded use of displacement as a preparative method, there has been renewed interest in using displacement chromatography in analytical and semi-preparative applications for enrichment of trace compounds.55 56... 

Drager, R. R. and Regnier, F. E., Application of the stoichiometric displacement model of retention to anion-exchange chromatography of nucleic acids,... 

Dendrimers are being used as host molecules, catalysts, self-assembling nanostructures analogs of proteins, enzymes, and viruses and in analytical applications including in ion-exchange displacement chromatography and electrokinetic chromatography. 

---