Prediction of Chromatographic Behavior

The usual basis of predictions of migratory behavior of ions in geological strata is the treatment of this behavior as an equilibrium chromatographic elution (], 2). This then leads to the following expression for the migratory velocity (v) of a species ... 

The derivation of these different retention equations is important in several respects. First, they allow for calculation of micelle-solute binding constants, parameters which are important in many areas of micellar kinetics or chemistry. There have been several reports in the literature demonstrating this chromatographic approach for determination of micelle - solute binding constants (1,8,104,105). More importantly, they allow for prediction of retention behavior as a function of surfactant concentration (or of pH at constant micelle concentration), provided that the micelle - solute binding constant (or solute ionization constant) is known (which can be determined spectroscopically or from kinetic studies) (1,96,102). Consequently, the theory allows the chromatographer to determine the optimum conditions required for a desired separation. 

Another mode of chromatographic behavior was predicted and verified [3] when enthalpic and entropic contributions to the distribution coefficient balance out, that is, when the change in free energy disappears (AG = 0). This mode is called liquid chromatography at the critical adsorption point (LCCC). The polymeric nature of the sample (i.e., the repeating units) does not contribute to the retention of the species. Only structural defects like end-groups, comonomers, or branching points contribute to the separation. 

The model, therefore, predicts the elution behavior of solutes during a chromatographic process over a swollen gel as the stationary phase as a function of solute size and of the gel nanomorphology. On the reverse, from the elution behavior of solutes of known molecular size it is possible to extract the polymer chain concentration from chromatographic experiments, where an unknown swollen gel is the stationary phase. This is the basis of the ISEC, which is so often mentioned through this chapter [16,17,105,106]. 

Most publications dealing with chromatographic reactors focus on theoretical issues of this very complex system. Models of different complexity were derived and used to predict the behavior of chromatographic reactors. Such models typically take into consideration different types of mass transfer, adsorption isotherms, flow profiles, and reactions. A general scheme of these models, not including the reaction, is presented in Fig. 4. There are also several review papers... 

Table 3 (73) compares the retention coefficients for synthetic peptides from various sources. To ensure comparability, the data has been standardized with respect to lysine and assigned a value of 100. The table shows that there are discrepancies between the results obtained using different chromatographic systems. Predictions of retention times should therefore be made using chromatographic systems similar to those used to calculate the retention coefficients for the amino acids. Casal et al. (75a) have made a comparative study of the prediction of the retention behavior of small peptides in several columns by using partial least squares and multiple linear regression analysis. 

Analytical chromatographic options, based on linear and nonlinear elution optimization approaches, have a number of features in common with the preparative methods of biopolymer purification. In particular, both analytical and preparative HPLC methods involve an interplay of secondary equilibrium and within the time scale of the separation nonequilibrium processes. The consequences of this plural behavior are that retention and band-broadening phenomena rarely (if ever) exhibit ideal linear elution behavior over a wide range of experimental conditions. First-order dependencies, as predicted from chromatographic theory based on near-equilibrium assumptions with low molecular weight compounds, are observed only within a relatively narrow range of conditions for polypeptides and proteins. 

This review will illustrate examples of computer projected models of inclusion complexes of structural isomers (ortho, meta, para nitrophenol), enantiomers (d- and 1- propranolol) and diastereomers [cis and trans. l(p-B-dimethylaminoethoxy-phenyl-butene), tamoxifen] in either a- or B-cyclodextrin. The use of these computer projections of the crystal structures of these complexes allows for the demonstration and prediction of the chromatographic behavior of these agents on immobilized cyclodextrin. 

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