Linkage Abundance and Molecular Weight Characteristics of Technical Lignins by Attenuated Total Reflection‐FTIR Spectroscopy Combined with Multivariate Analysis

Abstract

Lignin is an attractive material for the production of renewable chemicals, materials and energy. However, utilization is hampered by its highly complex and variable chemical structure, which requires an extensive suite of analytical instruments to characterize. Here, we demonstrate that straightforward attenuated total reflection (ATR)‐FTIR analysis combined with principle component analysis (PCA) and partial least squares (PLS) modelling can provide remarkable insight into the structure of technical lignins, giving quantitative results that are comparable to standard gel‐permeation chromatography (GPC) and 2D heteronuclear single quantum coherence (HSQC) NMR methods. First, a calibration set of 54 different technical (fractionated) lignin samples, covering kraft, soda and organosolv processes, were prepared and analyzed using traditional GPC and NMR methods, as well as by readily accessible ATR‐FTIR spectroscopy. PLS models correlating the ATR‐FTIR spectra of the broad set of lignins with GPC and NMR measurements were found to have excellent coefficients of determination ( R 2 Cal.>0.85) for molecular weight ( M n , M w ) and inter‐unit abundances (β‐ O ‐4, β‐5 and β‐β), with low relative errors (6.2–14 %) as estimated from cross‐validation results. PLS analysis of a second set of 28 samples containing exclusively (fractionated) kraft lignins showed further improved prediction ability, with relative errors of 3.8–13 %, and the resulting model could predict the structural characteristics of an independent validation set of lignins with good accuracy. The results highlight the potential utility of this methodology for streamlining and expediting the often complex and time consuming technical lignin characterization process.

Comparing chemical composition and lignin structure of Miscanthus x giganteus and Miscanthus nagara harvested in autumn and spring and separated into stems and leaves

“…Here, multivariate data analysis is a very helpful tool to "extract" details that are not available using conventional univariate analysis as shown also by other groups for lignins of different origin and pre-treatment method. 71,72 In a previous study, we also used chemometric processing of infrared data to specify differences of lignins obtained from six different Miscanthus genotypes including M. nagara (NagG10) and M. x giganteus (Gig35) separated by plant portions: stem versus leaf-derived lignins could be differentiated by their aromatic in-plane deformation signals at 1160 cm À1 corresponding to the monolignol substitution pattern. 61…”

“…Here, multivariate data processing (such as partial component analysis, linear discriminant analysis, factorial discriminant analysis and partial least squares-discriminant analysis) proved to be a useful tool for origin specication of complex structures such as lignocellulosic biomass, especially lignin. 71,72,[93][94][95][96][97][98][99] Moreover, Brandt et al emphasized that quantication using HSQC is generally limited since pulse sequences are usually optimized for resolution and signal strength. In addition, signal relaxation might not be complete particularly for some slowly relaxing end groups.…”

Lignin for Nano‐ and Microscaled Carrier Systems: Applications, Trends, and Challenges

“…In recent years, apart from its combustion for energy, isolation of lignin originating from industrial kraft pulping processes as well as biorefinery plants producing ethanol as biofuel has seen a steady increase. Parallel to the surge in the availability of lignin, nano‐ and microscaled lignin‐based materials and state‐of‐the‐art analytical techniques that provide a more detailed understanding of the structural differences of the various lignins were developed …”

Low-Input Crops as Lignocellulosic Feedstock for Second-Generation Biorefineries and the Potential of Chemometrics in Biomass Quality Control

“…Very recently, Lancefield et al reported a study on lignin 3D structure analysis using attenuated total reflection (ATR)-FTIR analysis combined with PCA and PLS modeling. In addition, the obtained quantitative results were comparable to gel-permeation chromatography (GPC) and 2D heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) methods [131].…”

“…Within the last five years, a tremendous number of LCF analysis studies have been reported, some of which include chemometric data processing (Table 3) [131,134]. For example, in 2014 Da Costa et al reported an LCF cell-wall analysis study, including 25 Miscanthus genotypes of different developmental stages separated into stem and leaf portions.…”