A study of aqueous solutions of dextrans by gel permeation chromatography using a multiple detection system

Abstract

AbstractWe studied the elution of dextrans in gel permeation chromatography (GPC) using a low‐angle laser light‐scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight‐average molecular weights (M̄w) are obtained from them. If instead of pure water a salt solution (0.1 M KNO3) is used as eluant, the charge effect is completely suppressed and single‐peak chromatograms are found. Again correct values of M̄w are obtained, but number‐average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M̄n could be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules, was observed.