Principles and Practice of Chromatography - The Development Process > Elution Development > Page 8


Other distribution functions might be more appropriate, but the specific nature of the function used will not affect the following explanation and so, for simplicity, the Gaussian function is assumed. The number of molecules at the boundary surface (N1) that have a kinetic energy in excess of the potential energy associated with their molecular interactions with the stationary phase (EA), (i.e., those molecules represented by the red area of the distribution curve) will leave the stationary phase and enter the mobile phase. Those with an energy less than (EA) will remain in the stationary phase. The distribution of energy of the solute molecules in the mobile phase is depicted in Figure 2B. The distribution is again taken as Gaussian in form and it is seen that the number of molecules (N2) striking the surface that have an energy less than (EA) (i.e., the red area in figure 2B) will remain in the stationary phase after entering the liquid, whereas the others having energies above (EA) will collide with the surface and 'rebound'. 'Rebound' is, perhaps, a somewhat inappropriate term in this context. In fact, some may rebound, others may communicate their excess energy to a another solute molecule which will give it sufficient energy to enter the mobile phase.


In either case, the net effect is the same; there will be no net molecule transfer if its energy is too great.