ASTM F2259-03 (2008) – Determining the Chemical Composition of Alginates by 1H NMR Spectroscopy

Alginate is a linear polysaccharide composed of mannuronate (M) and a-L-guluronate (G). The polysaccharide is characterized by the relative ratio of M/G, G-Content, and average length of blocks of G in the polymer. M and G are:

ASTM F2259 recounts the standard sample preparation and 1H NMR analysis that allows the following parameters to be calculated:

The 1H Spectra obtained on a typical alginate sample are show below:


Finally the peaks representing the individual M and G components and sequences are deconvoluted from the spectrum.
The intensities obtained from the deconvolution are input into the excel spreadsheet shown above and the various ratios, M and G content and a series of diads and triads are calculated along with some G block lkength information. It is the block length information that often reveals telling differences between samples.

Process NMR Associates performs this analysis at a cost of $225 per sample. The samples, however, must be prepared by the customer using the methodology set forth in the test method.