Characterization of nitrogen-containing compounds in coal tar and its subfractions by comprehensive two-dimensional GC × GC-TOF and ESI FT-ICR mass spectrometry based on new separation method

The molecular composition and structure of heavy oil and the subfraction have always been one of the most controversial topics despite the continuous improvement of detection and analytical methods. In this contribution, the composition and structure of nitrogen-containing compounds (NCs) in middle and low temperature coal tar (MLCT) and the subfractions are studied by GC × GC-TOF MS and ESI FT-ICR MS coupled with collision-induced dissociation (CID) through isolating a narrow window of mass-defined ions based on the developed MLCT subfraction separation method. It is found that the new separation subfraction method combined with high resolution mass spectrometry is efficient to detect the characteristics of each fraction at the molecular level. Eighty nitrogen compounds, dominant of quinolines, carbazoles and pyridines are identified in MLCT. The distribution laws of compound classes, carbon numbers, DBE are obtained with reasonable representative molecules for aromatic, resin and asphaltene. The qualitative analysis shows the island and archipelago structural motifs coexist in MLCT and the island-type is the predominant structure in aromatic (94%), resin (86%) and asphaltene (80%). The archipelagic structures in large molecules are more abundant. Meanwhile, the heterolysis mode is the predominant bond cleavages path for MLCT molecules and the proton transfers reactions occur during CID process. •The structure of coal tar molecules is studied by FT-ICR MS coupled with GC×GC-TOF MS based on new separation method.•The distributions of island and archipelago structural motifs in coal tar subfractions are obtained by qualitative method.•The bond cleavage behaviors are innovatively analyzed for large molecules in coal tar.