Ion Chromatography - Dispersion by Resistance to Mass Transfer in the Stationary Phase

 

Dispersion resulting from the resistance to mass transfer in the stationary phase is exactly analogous to the effect of resistance to mass transfer in the mobile phase. Those solute molecules close to the surface of the stationary phase will leave the surface and enter the mobile phase a significant time before those that have diffused further into the stationary phase and have longer distance to diffuse back to the surface. Thus, while the molecules remaining in the stationary phase diffuse to the surface the molecules in the mobile phase are swept along the column. The dispersion process involved in the transfer of solute molecules from the stationary phase to the mobile phase is diagramatically represented in figure 11. Again, considering six molecules in the stationary phase, molecules 1 and 2, the two closest to the surface, will enter the mobile phase and start moving down the column. The movement will continue while molecules 3 and 4 diffuse to the surface at which time they will also enter the mobile phase and follow molecules 1 and 2 down the column.

 

 

Figure 11. Dispersion by the Process of Mass Transfer in the Stationary Phase.