Displacement chromatography developing

FIG. 16-30 Operational steps in displacement chromatography, The column, initially equilibrated with a carrier solvent at time 0, is loaded with feed until time tp and supplied with displacer for a time to + tp. Development of the displacement train occurs during the time to and elution of the separated products ends at time tp. tp is the time required to remove the displacer from the column and restore the initial conditions, Components are niimhered in order of decreasing affinity for the stationary phase, [Reference Horoath et at, J, Ghromatogr, 2i8, 365 (1981). Reprinted with peimission of], Ghromatogr,]... 

Displacement Development A complete prediction of displacement chromatography accounting for rate factors requires a numerical solution since the adsorption equilibrium is nonlinear and intrinsically competitive. When the column efficiency is high, however, useful predictious can be obtained with the local equilibrium theoiy (see Fixed Bed Transitions ). 

Two case studies will be shown here to demonstrate the development of purification processes in both overload and resolution based separations 51]. The first example summarizes the purification of a synthetic peptide by overload chromatography, or more accurately described as sample self displacement chromatography The techniques applied to this separation are applicable to any molecule and can be applied to all modes of chromatography, with the exception of size exclusion chromatography. 

The Langmiur isotherm—used by Guiochon and others in the study of preparative scale chromatography—is based on the concept that adsorption nonlinearity occurs when there are so many molecules that they compete with one another for a limited number of adsorption sites. It is obvious that when two concentrated solutes are present at the same time, they will interfere with one another s adsorption. The one that adsorbs most strongly will almost totally displace the weaker adsorber. This is the basis of displacement chromatography, a nonlinear form developed by Tiselius in 1943 (17) and revived recently by Horvath [18]. 

The latter system is used at TRU, while the SRL development program demonstrated the suitability of displacement chromatography. Both methods appear to be satisfactory. Until now, and for the foreseeable future, the quantity of transcurium elements has been too small to justify any process other than elution development for the final separation. 

Methods development for displacement chromatography has been previously described for a Langmuirian system using a graphical approach which employs the adsorption isotherms for the displacer and the various components... 

FIGURE 12 Flow sheet for methods development in displacement chromatography. 

The development of displacement separations has historically been an empirical process and even though chromatographic theory may guide the selection of operating conditions the final stage must involve experimental validation. Typically, several experiments will be carried out at or near the conditions determined by the theory. The final stage in the procedure is either experimental or numerical optimization of the displacement process to produce optimal yields, purities and productivities. At this point, the relative efficacy of selective and conventional displacement chromatography can also be evaluated. 

Frenz, J., and Horvath, Cs. (1985). High Performance Displacement Chromatography Calculation and experimental verification of zone development. AIChE J. 31, 400-409. 

Displacement chromatography offers an attractive alternative to the elution mode of operation for preparative purification (S. Cramer, personal communication, 1999). Further investigations must be carried out to identify more cost-effective, nontoxic, and readily detectable displacers that are commercially available to the biotechnology industries. Displacers with high affinities in a range of commercially available stationary phases must be identified to facilitate the development of displacement steps on these materials. This will require significant advances in our understanding of the nature of affinity of these systems. 

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