LAUSR

Unlabeled and deuterium labeled dimeric lignin model compounds with β-O-4 linkages were evaporated and ionized us-ing negative ion mode electrospray ionization, transferred into a linear quadrupole ion trap, isolated and subjected to collision-activated dissociation (CAD; MS2 experiments). The elemental compositions of the fragment ions were deter-mined by using a high-resolution Orbitrap mass analyzer and their structures were examined using further CAD experi-ments (MSn experiments wherein n = 2-5). Data analysis was facilitated by determining the fragmentation pathways for several deprotonated model compounds. The structures of the key fragment ions of several pathways were determined by comparison of the CAD mass spectra measured for undeuterated and deuterated analogs and for deprotonated au-thentic compounds. Some of the proposed reaction mechanisms were tested by examining additional deprotonated syn-thetic model compounds. Quantum chemical calculations were used to delineate the most likely reaction pathways and reaction mechanisms. This work provides basic information needed for the design of tandem mass spectrometry-based CAD sequencing strategies for mixtures of lignin degradation products.