Distribution Coefficient (Kd) in Gel filtration (GF) / Size Exclusion Chromatography (SEC)

In gel filtration, distribution of particular compound between the inner and outer mobile phase is a function of its molecular size, which is represented by distribution coefficient (Kd).The larger molecules which is usually excluded from the gel beads, such molecules will have a Kd value of zero.Certain molecules which is smaller than the pore size of the gel  beads enters the pores in the gel matrix hence they will have a Kd value of one.For molecules of intermediate size, they will have Kd value between zero and one.This type of variation in the Kd Values makes it possible to separate molecules in the narrow molecular size range.