Solute retention mechanism in SEC

When considering the possible modes of solute retention in SEC it is important to first define the compartmentalization of volumes found within the size exclusion column. The total geometrical volume of the column, Vg, is defined as the sum of the total mobile phase volume, V, and the volume of the packing material or stationary phase, V. The mobile phase volume is further defined as the sum of the volume external to the beads constituting the packing material or the void volume, Vq, and the volume of the channels within the beads, V. The differential solute distribution between the spaces internal to and external to the pores in the column packing material results in the separation of the solutes on the basis of molecular size. In the absence of reversible adsorption, the average elution volume, Vg, is the sum of the void volume occupied by all solutes and a portion of the internal pore-volume defined by the size exclusion equilibrium constant, [Note that this 

Reversible adsorption, where it occurs, requires the addition of a third term, KlcVs where, Ky. is the distribution coefficient resulting from this process. However, in the practice of SEC one attempts to reduce adsorptive effects as much as possible using inert packing materials, thereby making this term insignificant. 

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