C CP/MAS analysis for estimating non-degradative lignin content

Xin Gao

Klason and acetyl bromide analysis were the most widely utilized chemical methods for lignin content analysis. Currently pyrolysis GC/MS, nitrobenzene oxidation and thioacidolysis, as well as different infrared and near-infrared techniques were also applied to lignin content determination. However, these methods were limited by their different drawbacks, and none of them can be employed without dissociation/degradation and/or pre-conditioning steps. Therefore, establishing a simple method that aims to accurately and reliably analyze the content from various lignocellulosic biomasses without destroying their native structure is desirable for lignin analysis. In this research effort, an improved non-degradative approach for accurately calculating the content of lignin in native biomass was established. This was accomplished by extending the scope of solid state 13C CP/MAS NMR technique via homogeneous mixing of an internal standard (TMSP) with varying lignin contents, thereby generating a standard curve for calculating the lignin content of variety of biomass without dissociation or degradation. The ratio of normalized area of lignin versus internal standard (TMSP) was plotted linearly and the response factor for lignin concentration was achieved from the corresponding linear equation. Internal validation results showed that the standard curve was reliable and stable, absolute relative errors were no more than 1.00%. In order to verify this method, several test samples have been tested. The results showed high accuracy on determination of their lignin content. Compared to chemical degradative method, such as acetyl bromide method, the relative difference was less than 5.00%. The study demonstrated the quantitative potential of solid state 13C CP/MAS NMR, when coupled with internal standard (TMSP). Also, it showed the potential to apply to different kinds of biomass. Furthermore, it can be used to estimate lignin content of some samples (acid insoluble lignin), which is difficult to analyze accurately using chemical methods. Overall, this method is easy, simple and accurate. It can serve as an efficient methodology for estimating lignin content.

C CP/MAS analysis for estimating non-degradative lignin content

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