Separation of Oligosaccharides with Gel Filtration 



Per Flodin and KAre Aspberg 



Research Laboratory, AB Pharmacia and the Institute of Biochemistry, 



Uppsala, Sweden 



In a series of oligosaccharides the individual members differ very 

 little in properties and the preparation of them requires highly selective 

 methods. Dickey and Wolfrom [i] succeeded in separating the acetylated 

 cellodextrins up to the cellohexaose chromatographically in magnesium 

 and calcium silicate columns. The acetates were adsorbed from a chloro- 

 form solution and the chromatogram was developed with a benzene- 

 ethanol mixture. The most commonly used procedure is to adsorb the 

 oligosaccharide mixture on charcoal from a water solution and then elute 

 them with a gradient of increasing ethanol concentration [2]. With minor 

 modifications the method has been applied to cellodextrins, maltodextrins 

 and isomaltodextrins. The selectivity is large enough to give a complete 

 separation up to the hexaoses. The higher members are generally obtained 

 as fairly pure substances containing the neighbouring oligosaccharides as 

 contaminants. 



In an ion exchange resin sucrose and glucose move at different rates 

 when conditions are chosen so that no adsorption takes place. Similarly, 

 in swollen starch the retardation is smaller the higher the degree of 

 polymerization [3]. 



In columns packed with particular gels formed by cross-linking 

 dextran, large molecules were observed to emerge first from the column 

 while small molecules were retarded [4]. The same phenomenon was 

 observed when low molecular weight dextrans were fractionated [5]. It 

 should be mentioned that all operations were made in the same solvent. 

 The behaviour is in contrast to what occurs in the adsorption chromato- 

 graphic techniques, where adsorption is stronger the higher the molecular 

 weight. It is consistent with a molecular sieve mechanism according to 

 which a larger part of the gel particle is available the smaller the molecular 

 size. The object of this communication is to show that the method, which 

 has been named gel filtration, may be used to separate cellodextrins. 



Experimental 



The dextran gel used was Sephadex G-25 (Pharmacia, Uppsala, 

 Sweden) 200-400 mesh dry sieved. It was swollen in water and sedi- 



