Electrospray Ionization with High-Resolution Mass Spectrometry as a Tool for Lignomics: Lignin Mass Spectrum Deconvolution

Capability to characterize lignin, lignocellulose, and their degradation products is essential for development of new renewable feedstocks. Electrospray ionization high-resolution time-offlight mass spectrometry (ESI HR TOF MS) method was developed expanding the lignomics toolkit while targeting the simultaneous detection of low and high molecular weight (MW) lignin species. The effect of a broad range of electrolytes and various ionization conditions on ion formation and ionization effectiveness was studied using a suite of mono-, di- and triarene lignin model compounds as well as intact lignin. Contrary to the previous studies, the positive ionization mode was found to be more effective for methoxy-substituted arenes and polyphenols, i.e., species of a broadly varied MW structurally similar to the native lignin. For the first time, we report an effective formation of multiply charged species of lignin with the subsequent mass spectrum deconvolution in the presence of 100 mmol·L-1 formic acid in the positive ESI mode. The developed method enabled the detection of lignin species with an MW between 150 and 9,000 Da or higher, depending on the mass analyzer. The obtained Mn and Mw values of 1,500 and 2,500 Da, respectively, were in good agreement with those determined by gel permeation chromatography. Furthermore, the deconvoluted ESI mass spectrum was similar to that obtained with matrixassisted laser desorption/ionization (MALDI) TOF MS, yet featuring a higher signal-to-noise ratio. The formation of multiply charged species was confirmed with ESI ion mobility HR Q-TOF MS

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

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. (C) 2006 Elsevier B.V. All rights reserved