The characterization of molecular weight distribution and aggregation by asymmetrical flow field-flow fractionation of unmodified and oxidized alginate

After oxidation, the presence of aldehydes on alginate chains allows reaction with, making oxidized alginate (OA) attractive for selective functionalization and gelation (i.e. covalent-crosslinks). The molecular weight (MW) of OA is significantly reduced after oxidation. As MW determines mechanical properties and degradation of OA-based hydrogels, it is essential to precisely measure the MW of OAs as function of its degree of oxidation (DO). Size exclusion chromatography is used for the analysis of polymers, but it has limited ability to measure the distribution of polymers with high MW, without recognizing the presence of aggregates. This work describes the use of asymmetrical flow field-flow fractionation (AF4) coupled with refractive index and multi-angle light scattering detectors as an analytical method for the quantification of the MW of OAs. OAs with low DO (5–10%) had a weight average molecular weight (Mw) in the range of 35–67 kDa, with aldehydes concentration of 1–1.8 mmol/g. OAs with higher DO (35–50%) had lower Mw (20 kDa), with aldehyde concentration of 4.3–6.5 mmol/g. This is the first study reporting the comprehensive characterization of OAs using the precision of AF4 method to quantify their MW, and will contribute substantially to the formulation of OA-based hydrogels towards more advanced biomedical applications.