Characterization of the water-insoluble fraction from fast pyrolysis liquids (pyrolytic lignin) Part III. Molar mass characteristics by SEC, MALDI-TOF-MS, LDI-TOF-MS, and Py-FIMS

Abstract Matrix assisted laser desorption ionisation-time of flight-mass spectrometry (MALDI-TOF-MS), laser desorption ionisation-time of flight-mass spectrometry (LDI-TOF-MS) and temperature resolved analytical pyrolysis field ionisation mass spectrometry (Py-FIMS) have been applied for the first time on two pyrolytic lignins (PL's), precipitated from different aged bio oil, and four PL-fractions for molar mass characterization. The results were compared with data from size exclusion chromatography (SEC). SEC was the only method that allowed a mathematical calculation of molar mass characteristics such as average molecular weight (Mw), dispersity (D), and the molar mass at the peak maximum of the elugram (Mp). The SEC Mp values of PL-fractions differ from visually interpolated MALDI-TOF-MS measurements by 20%. MALDI-TOF-MS spectra showed detailed structures of the molar mass distribution (MMD) of PL and PL-fractions. Especially, the spectrum of one PL showed various local maxima with intervals of 170–200 Da. The size of these intervals could represent the average absolute molar mass of PL-monomers. MALDI-TOF-MS was limited by the influence of superposing matrix signals in the spectrum at low molar masses. LDI-TOF-MS showed clearer spectra than MALDI-TOF-MS in mass ranges below 400 Da. No signals were obtained for fractions with higher masses or whole PL. Intervals between main signals were mostly 14–16 Da. In spectra of different PL-fractions, corresponding main signals can vary between 2 and 4 Da. These mass differences indicate variations in the aliphatic region of the PL molecules. Py-FIMS spectra contained masses of thermally ejected, but unfragmented monomers and dimers. It was the only method, which allowed partial identification of monomeric and dimeric structures of all samples. The detected monomers correspond to known lignin derived compounds in bio oil, the detected dimers have some similarities to phenylcoumaran structures. PL from aged bio oil showed an increased content of higher oligomers and a higher average molecular weight.

[1]  S. Martinović,et al.  Laser desporption Fourier‐transform mass spectrometry of lignins , 1995 .

[2]  A. Jacobs,et al.  Absolute molar mass of lignins by size exclusion chromatography and MALDI-TOF mass spectroscopy , 2000 .

[3]  H. Schulten,et al.  Chemical characterization of the organic matter in forest soils by Curie point pyrolysis-GC/MS and pyrolysis-field ionization mass spectrometry , 1990 .

[4]  A. Oasmaa,et al.  Fast Pyrolysis of Forestry Residue. 3. Storage Stability of Liquid Fuel , 2003 .

[5]  Anthony V. Bridgwater,et al.  Fast pyrolysis of biomass : a handbook , 1999 .

[6]  M. Karas,et al.  Matrix‐Assisted Laser Desorption Mass Spectrometry of Lignins** , 1992 .

[7]  Dietrich Meier,et al.  Characterization of the water-insoluble fraction from pyrolysis oil (pyrolytic lignin). Part I. PY–GC/MS, FTIR, and functional groups , 2001 .

[8]  A. Di Tullio,et al.  Mass spectrometry in the biosynthetic and structural investigation of lignins. , 2004, Mass spectrometry reviews.

[9]  D. Meier,et al.  Characterization of the water-insoluble fraction from fast pyrolysis liquids (pyrolytic lignin) , 2001 .

[10]  Stephen Y. Lin,et al.  Methods in Lignin Chemistry , 1992, Springer Series in Wood Science.

[11]  Michael E. Himmel,et al.  Some Aspects of Lignin Characterization by High Performance Size Exclusion Chromatography Using Styrene Divinylbenzene Copolymer Gels , 1987 .

[12]  D. Meier,et al.  Direct liquefaction of different lignocellulosics and their constituents: 2. Molecular weight determination, gas chromatography, i.r. spectroscopy , 1986 .

[13]  P. Leinweber,et al.  Advances in analytical pyrolysis of soil organic matter , 1999 .