tosoh corp with average particle diameter of 20 u03bcm and average pore diameter of 2000 angstroms as the base material the packing material for the hydrophobic interaction chromatography was prepared a mixture of 20 g of g6000 pw washed and substituted with 1 4 dioxane 20 g of 1 4 dioxane 1 g of 1 2 epoxyoctane and 0 5 ml of boron trifluoride as catalyst was stirred and mixed for 6 hours at 45 u00b0 c to obtain a packing material hereinafter referred to as octyl 6 pw having octyl group for adsorbing plasmid and for hydrophobic interaction chromatography next employing a packing material for gel filtration chromatography g5000 pw from tosoh corp with average particle diameter of 20 u03bcm and average pore diameter of 950 angstroms as the base material a packing material with weak hydrohobicity was prepared a mixture of 20 g of g5000 pw 20 g of 1 4 dioxane 1 g of 1 2 epoxybutane and 0 5 ml of boron trifluoride as catalyst was stirred and mixed for 6 hours and at 45 u00b0 c to obtain a packing material hereinafter referred to as butyl 5 pw having butyl group for adsorbing rnas and proteins and for hydrophobic interaction chromatography each packing material was packed into a stainless steel column with inner diameter of 7 5 mm and length of 7 5 cm 2 separation of a plasmid by a combined use of hydrophobic interaction chromatography and ion exchange chromatography u2014 separation by hydrophobic interaction chromatography after escherichia coli having pbr 322 as a plasmid was cultured for 16 hours at 37 u00b0 c the medium was subjected to centrifugal separation for 20 minutes at 4 u00b0 c and 8000 rpm the precipitated escherichia.