Preparative chromatography adsorption

Nieoud R. M., Seidel-Morgenstem A. (1993) Adsorption Isotherms Experimental Determination and Applieation to Preparative Chromatography Simulated Moving Bed Basics and Applications, R. M Nieoud (ed.), Institut National Polyteehnique de Lorraine, Naney, Pranee, p. 4-34. 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

In some exceptional cases, however, can be given a definite meaning. This is so in the case of adsorption from dilute solutions [13,21]. Incidentally, these are the conditions usually encountered in preparative chromatography. Let us assume the compound numbered 1 to be the preferentially adsorbed. If its equilibrium concentration (x,) is negligibly small, from Equation 10.36 one obtains... 

In preparative chromatography, high feed concentrations are suitable and lead to nonlinear adsorption behaviors. The nonlinear (and related competitive) effects must absolutely be taken into account when evaluating the flow rates. This issue has barely been addressed in the literature.25-27... 

O. Daprcmoni, G.B, Cox and V. Briand. PREP 98. 1998 Imcrnaiional Symposium. Exhibit and Workshops on Preparative Chromatography. Ion Exchange. Adsorption/Desorption Processes, and Related Techniques, May. 31-June. 3, Washington D C., p. 129,... 

Validation issues are especially important in the analytical field when quantifications are made. However, it is also important to validate the adsorption isotherm model and its estimated parameters used in preparative chromatography. In contrast to the situation for the bioanalytical area in the pharmaceutical industry, there are few published reports on validation in the analytical biotechnological and in the isotherm parameter determination field, and there exists no detailed validation guidelines [16, 17], This is why much effort in this thesis is focused on the development of validated methods in both these fields. 

In this section a short overview is given of preparative chromatography and the determination of adsorption isotherm parameters - single and competitive - to be used for computer-assisted optimization of separations. 

Preparative chromatography is widely used for the purification of different compounds, but this procedure needs to be optimized to achieve the minimum production costs. This can be done by computer-assisted modeling. However, this approach requires a priori determination of accurate competitive adsorption isotherm parameters. The methods to determine this competitive information are poorly developed and hence often a time limiting step or even the reason why the computer-assisted optimization is still seldom used. In this thesis in papers IV-VI, a new injection method was developed that makes it possible to determine these competitive adsorption isotherm parameters more easily and faster than before. The use of this new... 

If mass transport occurs by surface diffusion (3b) a solute molecule is adsorbed and transported deeper into the pore system by movement along the pore surface. During the whole transport process, molecules are within the attraction forces of the adsorbent surface. Notably, the attractive forces between the surface and absorbed molecules are so strong (Zhang et al, 2003) that, for many common adsorpt— adsorbent systems encountered in preparative chromatography, surface diffusion is physically implausible (especially in charged adsorpt - charged surface interactions). 

The most dramatic difference between analytical and preparative chromatography is the extension of the working range of the adsorption isotherm into its nonlinear region. The behavior of single components as well as their mixtures over the complete range of the adsorption isotherm has, therefore, to be determined with great accuracy. 

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