SIZE-EXCLUSION CHROMATOGRAPHY AND DYNAMIC LIGHT-SCATTERING OF DEXTRANS IN WATER - EXPLANATION OF ION-EXCLUSION BEHAVIOR

The size-exclusion chromatographic (SEC) and ion-exclusion chromatogra phic (IEC) behaviour of dextrans in water was studied in combination w ith dynamic light scattering (DLS) of their fractions obtained from mi cropreparative SEC in water. Dextrans do not aggregate in dilute aqueo us solution, but very low dust particle contamination, of particle siz e 110-170 nm, was revealed from DLS measurements after its separation and its concentration enhancement by SEC. The ion exclusion of charged dextran molecules is the only cause of two excluded peaks observed in the SEC of dextrans in pure water. Model dextran oxidation experiment s were performed and mono- and dicarboxydextran were identified as for ming these ion-excluded peaks. An IEC-SEC experiment is capable of det ecting the presence of polysaccharide chains bearing one or two carbox yl groups only, and of resolving them from each other and from the unc harged chains of molecular masses up to 10(6) if pure water is used as the mobile phase. The presence of such low charge density macromolecu les appears to be a general feature of polysaccharides.