Molecular mass characterization of tannins by organic A4F – multidetection

Physicochemical characterization of tannins and more specifically size distribution determination is of high importance to evaluate their properties. Currently, this determination is still an analytical challenge. Furthermore, some reactions as oxidation of tannins make their structures more complex and have a major effect on their intrinsic physicochemical characteristics and particularly on their polymerization degrees and masses. In this way, it is valuable to have analytical tools that can provide reliable data about mass and condensation of tannins.

This work presents preliminary results on tannin mass characterization by organic Asymmetrical Flow Field Flow Fractionation (A4F) hyphenated with UV detector and Multi Angle Laser Light Scattering (MALLS). A4F is a fractionation technique based on the ability of polymer or macromolecules to diffuse under a field of carrier solvent (named crossflow) in a semi permeable channel. Small polymers, diffusing more than big ones, elute faster due to the parabolic main flow profile inside the channel. One of the main advantages of A4F compared to SEC is the lack of interactions (in optimized conditions) between analytes and the membrane covering the channel.

UV tuned at 280nm was used as a concentration detector for tannins, while MALLS detector allowed the mass of condensed compounds to be obtained. Pure ethanol was used both to solubilize tannins and as carrier.

Promising results were obtained. Molar mass distributions of different tannins (with various oxidation state and polymerization degree) were achieved with high recovery (greater than 90% for unfiltered sample solutions) and values obtained were in accordance with those expected.

These results present A4F – MALLS as a convincing and convenient tool for mass (Mw, Mn, Mz, ...) characterization of tannin and aggregation/polymerization monitoring of tannin.