Study of Lignin by Atmospheric Pressure Photoionization Orbitrap Mass Spectrometry: Effect of Spectral Resolution

Atmospheric pressure photoionization Orbitrap mass spectrometry is a promising tool for studying lignin. It ensures the detection of thousands of lignin oligomers with molecular weights of up to 1.5–2 kDa and the reliable determination of their elemental compositions. In the present work, the effects of the resolving power of the mass analyzer on the recorded mass spectra of lignins and the results of characterization of the molecular composition of the biopolymer were studied. The test sample was a native dioxane lignin preparation, isolated from cedar wood. The phenomenon of the suppression of signals of lignin oligomers in the region of high molecular weights with an increase in the resolving power of the mass analyzer because of decay processes in the ion trap is described. It has been shown that a spectral resolution of at least 70 000 ( M /Δ M , at m / z = 200) is required for screening purposes and the determination of the elemental compositions of low-molecular-weight lignin fractions. A detailed study of the molecular composition of lignin requires the use of spectral resolution of 280 000; it ensures a multiple increase in the number of detectable oligomers in the range of molecular weights above 1 kDa and also the reliable identification of signals of lignin–carbohydrate complexes.