A comparative study of matrix- and nano-assisted laser desorption/ionisation time-of-flight mass spectrometry of isolated and synthetic lignin

Abstract

Introduction: Lignin is the second most abundant biopolymer next to cellulose. However, because of the complexity of the heterogeneous macromolecules, it is difficult to elucidate the polymeric structures of lignin by conventional analytical methods.

Objective: To obtain the detailed structures of lignin, we comparatively applied nano-assisted laser desorption/ionisation time-of-flight mass spectrometry (NALDI-TOF MS) and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS).

Methodology: Synthetic lignin from coniferyl alcohol and an isolated lignin from Pinus densiflora were subjected to NALDI- and MALDI-TOF MS.

Results: We first obtained NALDI-TOF MS of synthetic and isolated lignin. Mass increments of 178 and 196 Da were observed in NALDI- and MALDI-TOF mass spectra of the synthetic and isolated lignin. The mass intervals indicated that radical coupling forming β-O-4 bonds is the major pathway. Peaks in the low molecular mass region between m/z 500 and 800 were observed more extensively using NALDI-TOF MS than MALDI-TOF MS, which enabled detailed analysis of the interunit linkages in lignin.

Conclusion: Owing to the ionisation profile differentiation from MALDI-TOF MS, NALDI-TOF MS is useful for the structural analysis of lignin.