By Jon Lundqvist, R&D scientist
Selectivity is a measure of the relative retention of two solutes in a column related to the distance between two peaks in a chromatogram. The fractionation range/molecular weight range depends on the pore size distribution of the resin and specifies the range of molecular weights that have partial access to the pores of the resin. This means that molecules within this range should be separable.
The exclusion limit for a SEC resin specifies the size of the molecules that are too big to enter the pores and are therefore eluted in the void volume.
Read more to learn why describing the pore of a size exclusion chromatography resin with a single number such as average pore diameter is an oversimplification. The formation of pores is dependent on complex combinations of many parameters.