Chromatographic determination model, general

Generally, the transport parameter used is the logarithm of the partition coefficient of the bas (bioactive substance) or some quantity derived from it. The partition coefficient is almost always determined between water and 1-octanol. Parameters obtained by chromatographic methods are being used with increasing frequency however. The term in t2 is introduced to account for the frequently observed parabolic dependence of a data set of bas on the transport parameter. Models other than... 

With the considerable improvement in the ntunerical techniques that have taken place in the last 25 years and which allows now for very rapid munerical solutions of chromatographic models, the best approach appears to be the determination of initial estimates of the mass transfer parameters by moment analysis, combined with a final optimization of these estimates of the parameters by direct matching of the experimental response curves with the profiles derived from the general rate model in the time domain. 

The general rate model was used as a basis for the development of a computer program for the simulation of chromatographic processes by Gu [53]. The solution of the partial differential equations in the nonlinear range of the adsorption isotherms can be obtained by application of numerical methods. One drawback for the modeling of real chromatographic separations with this model is the multitude of physical parameters, which cannot be determined experimentally and have to be estimated by approximations. In practice, these parameters are often only inaccurately fittable, so that a reasonable calculation is impossible. This model is rather applicable for theoretical studies [54]. 

Previonsly the inflnence of adsorbed material on contact angles has been seen to be important. In general, the stndy of adsorption has been prompted by its importance in catalysis and reactions at interfaces. The Langmnir-Hinshelwood model for the kinetics of snch reactions is popnlar and depends on the adsorption-desorption rates (Bondart and Djega-Mariadasson, 1984). The nature of adsorption also needs to be stndied to determine the viability of chromatographic separation processes for a given system. Its attraction is that it is one of the very few means for separating similar components, snch as isomers, azeotropes, etc., that are traditionally difficnlt (Holland and Liapis, 1983). 

A general advantage of QSRR is that the equations derived allow the prediction of retention indices for compounds structurally similar to those used to develop the model but not represented in the initial data set. An essential condition for derivation of significant quantitative relationships between retention data and molecular structure descriptors is the precision and reliability of the chromatographic data used. Although there are several potential sources of errors in routinely determined GC retention indices, the correlations obtained are often very promising and meaningful. 

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