On the characterization of polygalacturonate salts in dilute solution

Three de-esterified pectins have been studied by size exclusion chromatography (SEC) coupled with a multiangle laser light scattering detector. The molecular weight and radius of gyration distributions were established. The influence of the pore diameters of the membrane used to clarify the pectin solutions before SEC analysis was tested. Filtration through membranes 0·05 μm pore diameter removes high molecular weight material for which the measured radius of gyration is near to or higher than 0·04 μm. The origin of these large particles which are more compact and perhaps less sensitive to shear forces than the other fractions, was not investigated. Nevertheless, some high molecular weight matter cannot always be removed by filtration. As a consequence, the M w of the main fraction of the sample, excluding the high molecular weight matter, is usually low and represents roughly 85% of the initial sample weight. The use of a refractive index detector coupled with SEC, or the measurement of the average molecular weight by light scattering cannot always demonstrate the presence of a high molecular weight fraction in pectin solutions.