Analysis of Lignin Aromatic Structure in Wood Based on the IR Spectrum
A total of 17 softwoods and 48 hardwoods were analyzed by IR spectroscopy to examine if syringyl ratio (syringyl/(syringyl+guaiacyl)) calculated from nitrobenzene oxidation products can be precisely expressed by area ratios of characteristic peaks of lignin in IR spectrum. Area ratio of two peaks is referred to as that of two wavenumber domains, represented by “wavenumber 1/ wavenumber 2.” Examined peak area ratios were 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/(855+815). Among these ratios, log(1595/1509) and log(1275/1220) showed significant linear relationship with the syringyl ratios with a correlation coefficient of 0.98 for all 65 woods. These two ratios could also be used to distinguish all the hardwoods from the softwoods.
[Show abstract] [Hide abstract] ABSTRACT: As the attraction of creating biofuels and bio-based chemicals from lignocellulosic biomass has increased, researchers have been challenged with developing a better understanding of lignin structure, quantity and potential uses. Lignin has frequently been considered a waste-product from the deconstruction of plant cell walls, in attempts to isolate polysaccharides that can be hydrolyzed and fermented into fuel or other valuable commodities. In order to develop useful applications for lignin, accurate analytical instrumentation and methodologies are required to qualitatively and quantitatively assess, for example, what the structure of lignin looks like or how much lignin comprises a specific feedstock׳s cellular composition. During the past decade, various diverse strategies have been employed to elucidate the structure and composition of lignin. These techniques include using two-dimensional nuclear magnetic resonance to resolve overlapping spectral data, measuring biomass with vibrational spectroscopy to enable modeling of lignin content or monomeric ratios, methods to probe and quantify the linkages between lignin and polysaccharides, or refinements of established methods to provide higher throughput analyses, less use of consumables, etc. This review seeks to provide a comprehensive overview of many of the advancements achieved in evaluating key lignin attributes. Emphasis is placed on research endeavored in the last decade.0Comments 8Citations
- "MIR spectroscopy was employed to measure the S lignin ratio (S/S þG) of 17 softwoods and 48 hardwoods . Peak area ratios including 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/ (855 þ815) cm À 1 were calculated, and after plotting on a logarithmic scale, the 1595/1509 and 1275/1220 cm À 1 ratios were found to have the highest correlation coefficients (r ¼0.98) when compared to NBO results. "
[Show abstract] [Hide abstract] ABSTRACT: Background In order to rapidly and efficiently screen potential biofuel feedstock candidates for quintessential traits, robust high-throughput analytical techniques must be developed and honed. The traditional methods of measuring lignin syringyl/guaiacyl (S/G) ratio can be laborious, involve hazardous reagents, and/or be destructive. Vibrational spectroscopy can furnish high-throughput instrumentation without the limitations of the traditional techniques. Spectral data from mid-infrared, near-infrared, and Raman spectroscopies was combined with S/G ratios, obtained using pyrolysis molecular beam mass spectrometry, from 245 different eucalypt and Acacia trees across 17 species. Iterations of spectral processing allowed the assembly of robust predictive models using partial least squares (PLS). Results The PLS models were rigorously evaluated using three different randomly generated calibration and validation sets for each spectral processing approach. Root mean standard errors of prediction for validation sets were lowest for models comprised of Raman (0.13 to 0.16) and mid-infrared (0.13 to 0.15) spectral data, while near-infrared spectroscopy led to more erroneous predictions (0.18 to 0.21). Correlation coefficients (r) for the validation sets followed a similar pattern: Raman (0.89 to 0.91), mid-infrared (0.87 to 0.91), and near-infrared (0.79 to 0.82). These statistics signify that Raman and mid-infrared spectroscopy led to the most accurate predictions of S/G ratio in a diverse consortium of feedstocks. Conclusion Eucalypts present an attractive option for biofuel and biochemical production. Given the assortment of over 900 different species of Eucalyptus and Corymbia, in addition to various species of Acacia, it is necessary to isolate those possessing ideal biofuel traits. This research has demonstrated the validity of vibrational spectroscopy to efficiently partition different potential biofuel feedstocks according to lignin S/G ratio, significantly reducing experiment and analysis time and expense while providing non-destructive, accurate, global, predictive models encompassing a diverse array of feedstocks.0Comments 6Citations
- "These methods can be expensive, laborintensive , time-consuming, destructive, and/or utilize toxic reagents such as boron trifluoride etherate. Vibrational spectroscopy, including Raman, near-infrared (NIR), and mid-infrared (MIR) has been shown to provide non-destructive, high-throughput, qualitative and quantitative assessments of lignin S/G ratios (Table 1)1314151617181920212223242526. Typically, the spectral data are combined with analytical results from a traditional technique (pyrolysis/mass spectrometry, thioacidolysis/gas chromatography ) for a subset of the samples, and the use of multivariate analysis, including principal component analysis (PCA) and partial least squares regression (PLS) allows the formation of robust models capable of classifying and predicting the analytes for the remaining samples. "
- [Show abstract] [Hide abstract] ABSTRACT: Toona sinensis wood was analyzed for main chemical composition, trace element content, and wood cellulose crystallinity by FT-IR spectroscopy and X-ray diffraction of its native and extracted forms. The results showed that the ash and the extractives content of Toona sinensis wood were higher than for other leafy trees. The holo-cellulose, cellulose, and lignin content of the wood were 722.2, 458.3, and 213.1 mg g−1, respectively. Trace element content was: Ca 3.05 × 103, Mg 3.34 × 102, Fe 1.38 × 102, K 1.30 × 102, Na 58.0, Al 25.7, Zn 5.91, Cu 4.06, Mn 3.21, and Pb 0.534 μg g−1. Extraction of Toona sinensis wood resulted in no significant chemical changes but the band at 1,736 cm−1 of C=O in lignin and hemicelluloses disappeared and a band at 1,245 cm−1 of CO–OR in hemicelluloses and C–O in lignin shifted to 1,234 cm−1 and weakened only in the spectrum of the sample extracted with 1 % (w/w) aqueous sodium hydroxide. The FT-IR crystallinity index of the sample extracted with 1 % (w/w) aqueous sodium hydroxide was less than that of the original wood. The X-ray diffraction crystallinity indices of nitric acid–ethanol cellulose in T. sinensis wood was 0.786. These results indicate that T. sinensis wood probably has good flexibility and strength, and has the potential for use as a biomaterial and/or a bioenergy feedstock. Graphical abstract0Comments 3Citations