Fig. 5

Quantitative and characteristic insights of lignin. a Strategy of lignin quantification using internal standard. Chemical structure of internal standard is shown. Panel adapted with permission of ref [82]. b 1D ¹³C CP spectra of pure lignocellulose samples and cellulose-based sugarcane bagasse with calibration curve correlating the lignin contents with the area of the signal due to methoxyl groups in the ¹³C NMR spectra, obtained by deconvolution of the spectra. Panels adapted with permission of ref [83]. c Comparison of analytical methods for determining lignin unit ratios. Panels adapted with permission of ref [84]