Characterization of an Aqueous-Dissolved Anionic Polysaccharide Using Rheology and Size-Exclusion Chromatography with a Differential Refractive-Index and Low-Angle Laser-Light Scattering Detectors

Abstract

Abstract From the aqueous growth medium of Red Microalgae Porphyridium sp., anionic polysaccharide was separated by centrifugation and dialysis. Xylose, glucose, galactose, mannose, rhamnose, arabinose, methyl-pentoses, dimethyl-hexoses, glucuronic acid and sulfated sugar-units were identified as constituting monomers. By means of size-exclusion chromatography with differential refractive index and low-angle laser-light scattering (DRI/LALLS) detectors, an average molecular weight of 8.4 × 106 g/mol was determined. For the investigated sample concentrations in the range of 0.08–0.1 mg/mL, SEC separation based on decreasing molecular weight was not observed; however, decreasing particle/fragment dimensions with increasing retention volume were eluted. Rheological investigations at 20°C showed that an aqueous 0.05 M NaCl solution of the dissolved polysaccharide was non-Newtonian with high elasticity. By comparing the polymer-coil packing density of the anionic polysaccharide with three reference polysaccharides, a particle/fragment-packing similar to dextran coils was found. With information about packing density and absolute molecular weight, universal calibration enabled an estimation of dimensions for the constituting components of the anionic polysaccharide in terms of sphere-equivalent radii. The SEC-eluted polymer-coils were found in the range between ≈2–140 nm with a maximum mass occurring at ≈90 nm.