Dming the last few years gel filtration has become a widely applied met,hod for the separation of water-soluble substances of different molecular weights (l-3). A major factor in the rapid development of this technique has been the preparation of suitable gel substances, e.g., Sephadex. These substances, however, do not swell in common organic solvents and thus cannot be used for gel filtration of lipids and compounds wit,h similar solubility properties. Reports have appeared on the use of vulcanized latex (4) and cross-linked polyst,yrenes (5-7) for the separation of compounds soluble in nonpolar solvents. In the course of the present work the use of a cross-linked polystyrene in gel filtration of lipids was described (8).
The availability of Sephadex with different degrees of cross linking prompted us to investigate possible methods for conversion of Sephadex into a less hydrophilic substance that could be used for gel filtration of lipids. It was found that methylation of Sephadex yielded a product which was valuable for the eeparat,ion of lipid-soluble compounds. It was evident that the separations obtained with this material were not due exclusively to gel filtration. Preliminary results of this work have been reported (9).
While this manuscript was in preparation the use of an acetylated Sephadex for the separation of polymers was mentioned (10).
Methods
Preparation of Methylated Sephadex. Sephadex G-25 and G-50, fine, in head form, was purchased from AB Pharmacia, Uppsala, Sweden. The methylation procedure was an adapt,ation of the method described by Denham and Woodhouse (11) for cellulose. Sephadex, 100 gm, was added to 800 ml of 20% aqueous KOH in a two-necked S-liter round-bottomed flask. The mixture was left under mild stirring in a nitrogen atmosphere for 24 hr. Dimethyl sulfate, 200 ml, was added during 6-8 hr from a separatory funnel with continuous stirring. After standing for 24 hr the Sephadex was filtered off on a sintered glass funnel and washed with water, ethanol, water and 20% aqueous KOH. It was then suspended in 235