The study compares the efficiency of laser desorption/ionization (LDI) of six dimeric compounds, corresponding to the most important types of bonds between monomeric structural fragments of lignin macromolecules, on three types of different stainless steel target plates. It was found that ground steel target plates demonstrate the best results because of the uniform crystallization of analytes and good surface coverage. The most important ionization mechanisms for lignin oligomers with conjugated structures and increased acidity, along with protonation (cationization), involve the formation of molecular ions due to direct photoionization. For all of the studied compounds, partial in-source decay was observed, the contribution of which became significant at high laser fluence. The LDI method was successfully used to obtain mass spectra of low-molecular-weight products of the depolymerization of technical lignins. It was shown that the use of hybrid mass spectrometers with a quadrupole ion trap leads to an increase in the percentage of signals of protonated molecules in the mass spectra of lignin depolymerization products because of the occurrence of side ion-molecular reactions in the plume and ion trap.

An approach based on the use of carbon matrices is proposed to obtain MALDI mass spectra of the most important secondary plant metabolites, pentacyclic triterpenoids (PCTs). The best results were obtained using carboxylated carbon nanotubes as a matrix; they form the most homogeneous solid phase with PCTs on a MALDI target plate surface. The cationization of analytes with lithium ions made it possible to obtain the most intense signals in the mass spectra of betulin, lupeol, and betulinic acid and ensured limits of detection for these analytes at a level of 15–25 ng. Because of the occurrence of side processes of the hydration and dehydration of cationized molecules, as well as of the replacement of labile protons by lithium ions, the resulting mass spectra are characteristic for various classes of PCTs and allow their reliable detection without using tandem mass spectrometry. The developed approach was successfully tested on real samples of birch bark extracts, and also on extracts from cranberry and lingonberry peels.