Adsorption isotherm parameters

Etaulsifier Oiaracteristics. Tlie values for CHC , adsorption isotherm parameters and micellar specific surface for sodium lauryl sulitoate as previously reported ( ) have heen usea... 

Table 1. Adsorption isotherm parameters of CPA and 2,4-D with different pH (298 K).

For the simulation of SMB-separations efficient software packages,based on the Triangle-Theory, are commercially available. The number of columns, the column dimensions, the theoretical number of plates in the columns, the feed concentration, the bi-Langmuir adsorption isotherm parameters and the number of cycles need to be defined by the user. Then the separation is simulated and values for the flow rate ratios, the flow rates, the switching time and the quality of the separation, purity and yield, are calculated. Based on these values an actual separation can be performed. However, some optimization/further development is usually necessary, since the simulations are based on an ideal model and the derived parameters and results therefore can only be taken as indications for the test runs. 

A proof for die existence of the border can be found in a parameter of the above-mentioned model of supercritical adsorption isotherms. Parameter n" in Eq.(2) indicates a saturated amount of absolute adsorption, which is the maximum adsorbate... 

V. Validation of the accuracy of the perturbation peak method for determination of single and binary adsorption isotherm parameters in LC. 

Because of the limited surface capacity of the stationary phase, the column often operates under overloaded conditions. This is why a further increased sample load results in a smaller amount of the fraction adsorbed. Thus, nonlinear conditions prevail. A further complication in the preparative case is that the different types of components compete with each other for the same binding site, an effect that ultimately results in strong band interactions and band contaminations. The functions describing this complex behavior are called competitive adsorption isotherm parameters. Because of... 

The first section of this thesis deals with development and validation of analytical biotechnological methods for qualitative and quantitative analysis (papers I-II). The second section (papers III- VI) concerns the issue of isotherm parameters determination for preparative purposes. More particularly, this section deals with the validated characterization of phase systems through the determination of isotherm parameters and computer simulations (paper III) and with the development and validation of methods to determinate adsorption isotherm parameters directly from component mixtures (papers IV-VI). The two sections together have one important feature in common the development and validation of chromatographic methods for analytical and preparative purposes (papers I-VI). The intention of this summary is to give readers who are new in the area a general introduction to the fields described above. For a more detailed discussion, see papers I-VI. 

To develop a new injection technique for the perturbation peak method in order to determine adsorption isotherm parameters directly from binary (Paper IV-V) or quaternary mixtures (Paper... 

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. 

In adsorption chromatography the relevant functions are the adsorption isotherm parameters. Since there are no theoretical tools available to predict isotherms from physico-chemical data of the solute, solvent and adsorbent, these adsorption isotherm parameters have to be determined experimentally. When measuring the data, it is important to use a broad concentration range, i.e., including both the linear part of the isotherm as well as concentration close to saturation of the stationary phase. Despite the fact that there are several methods available to obtain adsorption isotherm parameters, the experimental determination of the isotherms is still far from being routine work. 

The FACP and ECP methods cannot be used to determine adsorption isotherm parameters from multicomponent mixtures. By contrast FA can be used to determine multi-component adsorption data but it is a complex and time-consuming process [124, 125],... 

The method of elution on a plateau was first suggested by Helfferich in Science more than forty years ago [126], In the PP method, the chromatographic column is equilibrated with a constant stream of molecules in the mobile phase and a concentration plateau is established. A perturbation is then accomplished by injecting a sample containing an excess or a deficiency of the molecules as compared to the concentration at the plateau. [118-120, 127], The response at the column outlet will be small peaks, known as perturbation peaks, and their retention times are used to determine the adsorption isotherm parameters. The retention time of the perturbation peak is related to the isotherm through the equation ... 

After the adsorption isotherm experiments have been completed, an isotherm equation must be chosen. This equation should fit the experimental data. Often are the experimental data (the experimental adsorption data acquired by the FA method or the perturbation retention times acquired by the PP method) only compared with the ones calculated using the adsorption isotherm parameters acquired from some adsorption isotherm models [131], This is sometimes the only validation done in this field [131], However, the adsorption isotherm parameters should preferably be validated in two step (1) the different isotherm models should be compared using statistical calculations, e.g., an F-test, and (2) by using the parameters to computer simulate elution profiles and then compare them with experimental ones. 

To conclude to which isotherm models the data fits best the values of the residuals should be used in an F-test [132], In paper III an F-test comparing different adsorption isotherm parameters is done and clearly explained. 

To validate the accuracy of the adsorption isotherm parameters determined experimentally, they could be used to computer simulate elution profiles, which then could be compared to experimental ones. So far, this has only been made by visual inspection [13, 118, 120, 128], In order to quantify and validate how well the simulation fits the experimental data we defined in papers III, V and VI, the overlap to be ... 

Determination of Single Component Adsorption Isotherm Parameters - Characterization of a New CSP (Paper III)... 

The accurate determination of the adsorption isotherm parameters of the two enantiomers on a CSP is of fundamental importance to do computer-assisted optimization to scale up the process. Such determinations are usually done with an analytical column and the most traditional method to determine the parameters and saturation capacity is by frontal analysis (see section 3.4.2). The aim of paper III was to investigate the adsorption behavior and the chiral capacity of the newly developed Kromasil CHI-TBB column using a typical model compound. Many of the previous studies from the group have been made on low-capacity protein columns which has revealed interesting information about the separation mechanism [103, 110, 111], For this reason a column really aimed for preparative chiral separations was chosen for investigation [134], As solute the enantiomers of 2-phenylbutyric acid was chosen. 

Figure 18. Isotherms for (R) and (S)-2-phenylbutyric acid, experimentally acquired by frontal analysis and compared with their fits with bi-Langmuir adsorption isotherm parameters. The lines are calculated data using the best single bi-Langmuir 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],... 

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... 

There are, so far, only two reports on the determination of isotherm data from mixtures containing more than two components. In both cases, the FA method was used for ternary mixtures [135, 136], There are no reports on the experimental determination of adsorption isotherms for quaternary mixtures using any chromatographic method. The competitive quaternary adsorption isotherm parameters could be very valuable for the separations of the four isomers of a compound with two chiral centers, or for the preparative separation of two compounds in the presence of one or two impurities. 

To conclude, in paper VI were for the first time ever the adsorption isotherm parameters successfully determined for a quaternary mixture. This was done using the newly developed injection technique with the PP method. Accurate adsorption isotherm parameters were determined without the need of pure components in large quantities. With our injection technique only about 0.3 mg of two of the components have to be available in... 

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... 

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. 

---