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Other publication - Peer-reviewed, 2010

Application of diffusion-edited NMR spectroscopy for selective suppression of water signal in the determination of monomer composition in alginates

Morssing Vilén Eric, Klinger Markus, Sandström Corine


Alginate, a structural polysaccharide in brown seaweeds, is a linear copolymer of 1-4 linked -D-Mannuronic acid (M) and 1-4 linked -L-Guluronic acid (G) residues. These residues are arranged in homopolymeric regions of M and G-blocks and regions of heteropolymeric MG-blocks. The chemical composition of alginates influences their physical properties, like gel properties and viscosity. Alginates are used in a vast range of industrial applications, many of which have different demand on the physical properties of the polysaccharide. Therefore it is of great importance to have methods, such as IR, Raman, nearIR and NMR, that accurately can determine the M/G-ratio. The viscosity of alginate samples is usually decreased by partial acid hydrolysis, which is time consuming and can possibly alter the sample. Instead samples of low concentration can be used. The drawback is that the residual water peak in the NMR spectrum is several orders of magnitude larger than the alginate signals so water suppression is needed. Commonly used techniques such as presaturation or pulse field gradient based techniques suffer from lack of specificity, and any other signals that overlap with the solvent peak will also be suppressed. These techniques have also been shown to alter the intensities of signals in NMR spectra of alginates [1], leading to significant errors in the calculation of the M/G-ratio. By using a diffusion-filtered NMR experiment the signal from water can be suppressed while retaining the signals of interest. This approach exploits the difference in translational diffusion between the larger, slowly diffusing, solute molecules and the smaller, faster diffusing, water molecules. Using this technique the monomer composition of alginate powders, covering a large range of M/G ratios and viscosities, has been determined. References [1] T. Salomonsen et al., Magnetic Resonance in Food Science, 12 (2009)

Published in

Book title: Book of Abstracts (Oral presentation)
Publisher: De 22:a Organikerdagarna