Conversion factors for carbohydrate analysis by hydrolysis and 1H-NMR spectroscopy

Abstract

Conversion factor to calibrate the lower xylan content in carbohydrate compositional analysis in wood by 1H-NMR spectroscopy was investigated. During acid hydrolysis, xylan monomer was dehydrated as furfural, and that furfural was further degraded or condensed in acidic reaction condition. Anomeric hydrogen peaks integration in 1H-NMR spectroscopic method excluded xylose reacted products (such as furfural and their condensed or degraded products). Only 52% of xylose was counted in anomeric hydrogen integration and 62% of xylose was counted in integration of furfural peak and anomeric hydrogen. For accurate carbohydrate compositional analysis by NMR spectroscopic method, furfural and their reacted products should be counted as xylose. Conversion factor for xylose content analysis was introduced from the acid hydrolysis of several different combinations of standard cellulose and xylan. In this study xylan conversion factor 0.66 was obtained based on compared NMR data from the prepared cellulose and xylan mixtures acid hydrolyzed with the same condition for woodmeal and pulps. With corrected xylan content calculation, NMR spectroscopic method gave rather closer carbohydrate composition compared to the other analytical methods.