Determination of Competitive Adsorption Isotherm Parameters

Single-component isotherm parameters cannot always predict elution profiles with satisfied accuracy [122, 123], Therefore, to be able to predict accurate overloaded multi-component elution profiles where competition occurs competitive adsorption isotherm parameters are often necessary. Measurement of isotherms from a mixture is also often necessary because the pure enantiomers are not always accessible in large quantities. However, there exist only a small number of reports on the determination of multi-component adsorption isotherm parameters. FA can be used to determine binary isotherm data but it is time-consuming. The PP method is an alternative method to determine isotherm parameters from binary mixtures. It has been reported that the PP method works well up to weakly non-linear conditions [118, 119], 

Because of this severe problem when using the PP method with the traditional blank injection technique we developed a new injection technique, called the Lindholm-technique . In this technique the injections should be done with the same excess of one of the compounds as deficiency of the other component Csample, = Cplateau, - u and f 

If the PP method is used in a multi-component case it should also be noted that the determined isotherm parameters could not be assigned to specific components without additional information, e.g., by comparing computer simulations with an experimental chromatogram where the peaks can be identified. 

The most practical and economical approach is to perform the PP method using only one mixture, but most often the PP method has been performed using several mixtures of various relative compositions to obtain high accuracy, the drawback being that this approach requires pure chemicals. No comparision and validation has been made of parameters determined by the PP method using only racemic mixtures compared to the PP method using several different enantiomer ratios. Hence, in paper V a comparison was done between adsorption isotherm parameters obtained from the PP method using different various relative compositions and from only racemic mixtures. The Lindholm-injection- technique developed in paper IV was used. 

The adsorption isotherm parameters obtained in paper IV were validated in two step (1) the experimental perturbation retention data were compared with the calculated retention data using the adsorption isotherm parameters, and (2) by using them with computer simulation programs to calculate elution profiles. The simulated profiles were compared with the experimental profiles using the calculations of the overlap (see section 3.6) as evaluation 

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I hope that my thesis can be used as a contribution in the future for analysis and validation in biotechnology, and also for the rapid determination of competitive adsorption isotherm parameters so that computer-assisted simulations may be used more extensively, in scaling-up and optimization of large scale chromatography. 

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