ABSTRACT
Chromatography, by definition, is a separation methodology for a multicomponent sample mixture, which is based on differentiating movement zones of the sample. An essential feature of chromatographic separation is that the components of the sample are transported through the separation medium-in the case of thin layer chromatography (TLC), through an open bed. Differences in interaction with the medium lead to a selective redistribution of the component zones, from overlapping zones at the start following injection, toward largely individual regions inside the separation medium. The appearance of individual component zones, after the development process, can be recorded with the aid of scanning densitometry, to convert the plate chromatogram into realistic two-dimensional representation of the chromatographic process in a form suitable for evaluation of kinetic parameters. The underlying fundamental processes responsible for chromatographic separations can be explained by thermodynamic and kinetic considerations. Thermodynamic relationships are responsible for retention and selectivity, and kinetic properties are responsible for band broadening. Thus, the position and separation of peaks in a chromatogram are thermodynamic properties, whereas the axial dimensions of the peaks are governed by kinetic considerations, and both phenomena must be considered to optimize resolution. As Giddings[1] emphases in his book, “separation is the art and science of maximizing separative transport relative to the dispersive transport.”
