Principles and Practice of Chromatography - The Development Process > Elution Development > Page 9

N1 = N2

This description of the dynamics of solute equilibrium is oversimplified, but is sufficiently accurate for the reader to understand the basic principles of solute distribution between two phases.

Consider distribution between a gaseous mobile phase and a liquid stationary phase. As the temperature is raised the energy distribution curve in the gas moves to a higher range of energies. Thus, as the column temperature is increased, more solute molecules in the stationary phase will randomly acquire sufficient energy (EA) to leave the stationary phase and enter the gas phase. Thus, the distribution coefficient of all solutes with respect to the stationary phase will be reduced as the temperature rises and it will be seen in due course that this will cause the band velocity of all the solutes to be increased.

Elution Development in Thin Layer Chromatography

The development processes that take place on a thin layer plate is complicated by the frontal analysis of the mobile phase itself. The mobile phases used to elute the solutes in TLC are usually multi-component, containing at least three individual solvents. If the plate is not pre-conditioned with solvent, there is an elaborate modification of the plate surface which is depicted, for a ternary solvent mixture, in Figure 3. The edge of the plate is dipped into a tray of the solvent mixture which begins to migrate along the plate, driven by surface tension forces. The different solvents array themselves on the surface in the manner shown in Figure 3.

Figure 3. The Development of a Thin Layer Plate