Abstract
Lignin is the second most abundant natural biopolymer and potentially a valuable alternative energy source for conventional fossil fuels. In this study, Fourier-transform ion cyclotron resonance-mass spectrometry (FTICR-MS) in conjunction with phase correction was applied to study photooxidation products of lignin using a 7 Tesla (T) mass spectrometer. The application of 7 T FTICR-MS has often been inadequate for the analysis of complex natural organic matter because of insufficient resolving power as compared with high-field FTICR, which led to incorrect assignments of elemental formulae and discontinuous plots in graphical and statistical analyses. Here, the application of phase correction to the FTICR mass spectra of lignin oxidation products greatly improved the spectral quality, and thus, readily permitted characterization of photooxidation processes of lignin compounds under simulated solar radiation conditions.
Highlights
Petroleum is the most important energy source today, which is unlikely to change in the foreseeable future
At m/z 679, the two close mass doublets (C38H32O12 and C35H36O12S) were only partially resolved in the magnitude mode display, whereas in absorption mode, they were almost baseline resolved, accompanied by a significant improvement of mass accuracy. This was generally observed in our lignin experiments; the phase correction method often resolved very close peaks that remained unresolved in the conventional magnitude mode mass spectra, along with greatly increased mass accuracy and a resulting lower number of possible elemental composition assignments in the lignin mass spectra obtained from low magnetic field FTICR-MS
Several other abundant low peaks were detected in comparison with the previous UV-oxidation experiments, which was due to the enhanced capabilities of the absorption mode mass spectral analysis used in the present study, offering greatly improved signal-to-noise ratio (S/N) and mass resolution over the previous study
Summary
Petroleum is the most important energy source today, which is unlikely to change in the foreseeable future. We used 2D KMD plots (Kendrick 1963) to recognize series of lignin compounds that contain a dibenzyl ether (C7H7O) linkage and methoxylation (OCH3) throughout the entire mass spectrum (Fig. S4); m/z windows of ∼10 mDa were expanded for the chosen compounds to compare the performance of the two mass spectral modes.
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