Estimation of Syringyl Units in Wood Lignins by FT-Raman Spectroscopy

Journal Article · Wed Mar 27 00:00:00 EDT 2019 · Journal of Agricultural and Food Chemistry

DOI:https://doi.org/10.1021/acs.jafc.8b06707· OSTI ID:1546618

Agarwal, Umesh P. ^[1]; Ralph, Sally A. ^[2]; Padmakshan, Dharshana ^[3]; Liu, Sarah ^[3]; Foster, Cliff E. ^[4]

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1. US Dept. of Agriculture (USDA), Madison, WI (United States); United States Department of Agriculture, Forest Service, Forest Products Laboratory
2. US Dept. of Agriculture (USDA), Madison, WI (United States)
3. Univ. of Wisconsin-Madison, Madison, WI (United States)
4. Michigan State Univ., East Lansing, MI (United States)

Syringyl (S) lignin content and the syringyl-to-guaiacyl (S/G) lignin ratio are important characteristics of wood and lignocellulosic biomass. While numerous methods are available for estimating S lignin units and the S/G ratio, in this work, a new method based on Raman spectroscopy that uses the 370 cm^–1 Raman band-area intensity (370-area) was developed. The reliability of the Raman method for determining S content was first tested by the quantitative analysis of three syringyl lignin models by sampling them, separately, in dioxane and in Avicel. Good linear correlations between the 370 cm^–1 intensity and model concentrations were obtained. Next, the percent syringyl (%S) lignin units in various woods were measured by correlating the 370 cm^–1 Raman intensity data with values of S units in lignin determined by three regularly used methods, namely, thioacidolysis, DFRC, and 2D-HSQC NMR. The former two methods take into account only the monomers cleaved from β–O–4-linked lignin units, whereas the NMR method reports S content on the whole cell wall lignin. When the 370-area intensities and %S values from the regularly used methods were correlated, good linear correlations were obtained (R² = 0.767, 0.731, and 0.804, respectively, for the three methods). The correlation with the highest R², i.e., with the 2D NMR approach, is introduced for estimating S units in wood lignins by Raman spectroscopy as, in principle, both represent the whole cell wall lignin and not just the portion of lignin that gets cleaved to release monomers. The Raman analysis method is quick, uses minimal harmful chemicals, is carried out nondestructively, and is insensitive to the wet or dry state of the sample. The only limitations are that the sample of wood contains at least 30% S and not be significantly fluorescent, although the latter can be mitigated in some cases.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
• Grant/Contract Number: FC02-07ER64494; SC0018409
• OSTI ID: 1546618
• Journal Information: Journal of Agricultural and Food Chemistry, Journal Name: Journal of Agricultural and Food Chemistry Journal Issue: 15 Vol. 67; ISSN 0021-8561
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
Cell wall
DFRC
NMR
percent syringyl
syringyl-to-guaiacyl lignin ratio
thioacidolysis