Characterizing polysaccharide structure with SEC-MALS and intrinsic viscosity measurements
In this application note, molecular weight data from the Viscotek SEC-MALS 20 is combined with measurements of Rg and IV to study the structure of different polysaccharides including pullulan, dextran, hydroxypropyl cellulose (HPC), pectin and gum Arabic. The differences between conformation and Mark-Houwink plots are also studied.
sponsored by Malvern Panalytical
Introduction
The physical properties and behavior of polymers and polysaccharides depends strongly on the properties of the molecules themselves. Molecular weight and molecular weight distribution, molecular size and structure all affect how the material will behave. Gel-permeation chromatography (GPC), also called size-exclusion chromatography (SEC), is the most commonly used tool for assessing these parameters.
The principle of GPC involves separating the sample as it travels through a porous but inert column matrix. While smaller molecules penetrate the pores more deeply, larger molecules are excluded and thus travel through the column faster. The result is a separation based on hydrodynamic volume but the desire is to know the molecular weight of the sample. Previously, molecular weight was estimated by comparing the elution time of the sample to that of standards of known molecular weight. Now, however, a light scattering detector is a common tool that allows polymer molecular weight to be measured independently of retention time. The concurrent measurement of Rg using multi-angle light scattering (MALS) and intrinsic viscosity offers exceptional insight into the structure of synthetic and natural polymer molecules as well as their molecular weight.
The Viscotek SEC-MALS 20 (figure 1) is a 20 angle light scattering device capable of making measurements of molecular weight and Rg (radius of gyration). It can be used as part of a multi-detector GPC system that combines light scattering with other detectors such as refractive index (RI), ultraviolet (UV) and intrinsic viscosity (IV) to generate a large amount of information about a sample simultaneously.
