Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > The Resistance to Mass Transfer in the stationary Phase > Page 24

The Resistance to Mass Transfer in the stationary Phase

The resistance to mass transfer in the Stationary phase is depicted in figure 8.

Figure 8. Resistance toMassTransferintheStationary Phase

The dispersion resulting from the resistance to mass transfer in the stationary phase can be described in the same way as that in the mobile phase. Molecules close to the surface of the stationary phase, will leave and enter the mobile phase before those that have diffused farther into the stationary phase and, thus, have further to diffuse back to the surface. Consequently, during the period required for the solute molecules to diffuse to the stationary phase surface, those molecules that were close to the surface will be swept along by the moving phase and dispersed from those molecules still diffusing to the surface. In figure 6,molecules 1 and 2, (the two closest to the surface) will enter the mobile phase and begin moving with the mobile phase along the column. This process will continue while molecules 3 and 4 diffuse to the interface at which time they, also, will enter the mobile phase and start following molecules 1 and 2 down the column. All four molecules will continue their journey down the column while molecules 5 and 6 diffuse to the mobile phase/stationary phase interface. By the time molecules 5 and 6 enter the mobile phase, the other four molecules will have been smeared along the column and the original 6 molecules will have suffered dispersion.