A complex matrix, heavy fuel oil (HFO) requires efficient chromatographic separation to fully characterize. Comprehensive two-dimensional gas chromatography (GCxGC) is coupled to a high-resolution time-of-flight mass spectrometer (HRTOFMS) for chromatographic separation of compound classes into structural bands before further categorization of compounds based on characteristic electron impact ionization (EI) fragmentation at standard 70eV. Positive chemical ionization (PCI) with methane as reagent gas allows for discovery of molecular ions for most hydrocarbon classes. Additionally, electron capture negative ionization (ECNI) provides yet another dimension of information. Use of a new multi-mode source (MMS) allows for acquisition of EI, PCI, and ECNI information without any changes to physical hardware, allowing chromatographic retention times between acquisition modes to remain unchanged. With so many dimensions of data both chromatographic and spectral, it is necessary to leverage a combination of interactive software tools such as filterable chromatographic contour plots to display compounds of interest and mass defect plots to leverage the high-resolution spectral information. The alignment of GCxGC retention times resulting from use of the MMS  further allows linking of peaks and spectral information between ionization modes for molecular ion confirmation with high isotopic fidelity of any automatically deconvoluted spectral library matches. Even in cases where no good spectral library match is found, tentative identification is possible when knowledge of the chromatographic separation is applied in conjunction with EI fragmentation, formula assignment for the molecular ion provided by PCI, and signal correlation with ECNI for compounds with halogenated substitution. After confident separation and identification of these species, ratios of known geochemical biomarkers can be used to further characterize both the environmental impact as well as the source origin of the HFO sample.

Tools for structural elucidation and comprehensive characterization of heavy fuel oils using multi-mode ionization on GCxGC-HRTOFMS

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ACS Fall 2022

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