Structural Characterization of Acidic Compounds in Pyrolysis Liquids Using Collision-Induced Dissociation and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

In this study, a
novel approach to characterize and identify acidic
oil compounds utilizing the fragmentational behavior of their corresponding
precursor ions is presented. Precursor ions of seven analyzed pyrolysis
oils that were generated from pyrolysis educts of different origins
and degrees of coalification were produced by electrospray ionization
in the negative ion mode (ESI(−)). Following a fragmentation
of all ions in the ion cloud by collision-induced dissociation (CID),
the precursor and product ions were subsequently detected by ultrahigh
resolving Fourier transform ion cyclotron resonance mass spectrometry
(FT-ICR-MS). The ESI(−)-CID data sets were evaluated by applying
either a targeted classification or untargeted clustering approach.
In the case of the targeted classification, 10% of the ionized precursor
ions of the analyzed pyrolysis liquid samples could be classified
into one of 11 compound classes utilizing theoretical fragmentation
pathways of these classes. In contrast, theoretical fragmentation
pathways were not necessary for the untargeted clustering approach,
making it the more transmittable method. Results from both approaches
were verified by analyzing standard compounds of known structure.
The analysis and data evaluation methods presented in this work can
be used to characterize complex organic mixtures, such as pyrolysis
oils, and their compounds in-depth on a structural level.