Potential and limitations of 13C CP/MAS NMR spectroscopy to determine the lignin content of lignocellulosic feedstock

Nuclear magnetic resonance (NMR) spectroscopy has been applied worldwide to study the chemical composition of lignocellulosic biomass and to analyse changes resulting from the chemical processing of these materials. In this work, solid-state C-13 NMR was used to study the lignin contents of a large set of lignocellulosic materials derived from various Brazilian plant species. To determine the lignin content by NMR, the integrated intensity of the deconvoluted signal due to methoxyl groups in the C-13 NMR spectra was used to obtain a calibration curve using mixtures of cellulose and lignin standards. The lignin contents obtained by NMR were, in general, in good agreement with the results obtained by methods based on acid hydrolysis (AH). For some samples, the NMR results showed that the AH methods were ineffective for the complete carbohydrate hydrolysis, indicating that the NMR-derived values represented more reliable estimates of the lignin contents in these cases.