STRUCTURAL CHARACTERIZATION OF LIGNIN POLYMERS BY TEMPERATURE-RESOLVED IN-SOURCE PYROLYSIS MASS-SPECTROMETRY AND CURIE-POINT PYROLYSIS-GAS CHROMATOGRAPHY MASS-SPECTROMETRY

Temperature-resolved in-source pyrolysis-mass spectrometry (Py-MS) and complementary Curie-point pyrolysis-gas chromatography/mass spectrome try (Py-GC/MS) were used to characterize a set of lignin polymers. No sample pretreatment was required and over 100 thermal degradation prod ucts were identified in the pyrolysates. Results were compared with wh ole biomass reference materials. Coniferyl alcohol and sinapyl alcohol , which were formed upon pyrolysis of lignin, could be selectively ion ized by ammonia chemical ionization (CI). Curie-point Py-GC with flame ionization detection was applied to classify the lignin polymers acco rding to syringyl/guaiacyl ratios, the number of preserved phenylpropa ne structural units and functional group content. Multivariate analysi s of the in-source Py-MS data was employed to classify the lignin poly mers according to the origin and degree of modification. Combined resu lts showed that enzyme-treated cottonwood-milled wood lignin is a rela tively homogeneous polymer with a large fraction of preserved alkyl-ar yl ether linkages. Technical lignins, isolated by the steam-explosion, organosolv and Kraft pulping processes, were found to be modified dep ending on the severity of the isolation procedure employed, and contai ned large amounts of beta-1-linked stilbene and beta-beta-linked resin ol types of structures. Bagasse lignin shows the most condensed polyme r structure with a large proportion of ether bonded p-coumaric acid an d ferulic acid.