Gel filtration is a technique of partition chromatography in which the partitioning  is based on the molecular size of the substances to be separated . In Gel Filtration chromatography, the stationary phase consists of porous beads with a well-defined range of pore sizes . proteins that are too large to fit inside any of the pores are said to be excluded .They have access only to the mobile phase between the beads and, therefore,elute first.