Multidimensional fractionation of wood-based tannins

[摘要] ENGLISH ABSTRACT: High molar mass tannin extracts are complex mixtures which are distributed in both molar mass and chemical composition. Condensed tannins from quebracho and mimosa and hydrolysable tannins of tara, chestnut wood and turkey gall were studied. Application of a single analytical technique is not sufficient to elucidate the complete structures present in the extracts. 13C Nuclear Magnetic Resonance (NMR) spectroscopy and Matrix Assisted Laser Desorption/Ionisation Time-of-Flight (MALDI-TOF) mass spectrometry were applied in order to determine the chemical composition and molar mass, respectively. A new mass spectrometric method that can uniquely determine the oligomer microstructure was developed using Collision Induced Dissociation (CID) experiments. Bulk analysis only showed the average composition of the extracts, in order to obtain specific information on the molar mass and chemical composition distributions. Hydrophilic Interaction Liquid Chromatography (HILIC) was used for analysis of the condensed tannins and for the hydrolysable tannins Normal Phase Liquid Chromatography (NP-LC) was utilised. The HILIC separation was up-scaled and the fractions were collected and analysed by MALDI-TOF, and this coupling revealed that separation occurs by molar and chemical composition. For separation of the molecules only by size, Size Exclusion Chromatography (SEC) analyses were carried out; this allowed for relative comparison of the tannin molecules. In conclusion, for characterisation of high molar mass tannins a multi-dimensional approach was necessary since the various distributions present in these extracts are superimposed.

[发布机构] Stellenbosch University