Characterization of polar compounds in a true boiling point distillation system using electrospray ionization FT-ICR mass spectrometry

In this work, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(+/-)-FT-ICR MS) was applied in the chemical characterization of polar compounds. These compounds were identified as the oxygen-containing compound classes (naphthenic acids, O2 class, and phenols, O1 class), the sulfur-containing compound classes (mainly sulfides, S1 class), and the basic and non-basic nitrogen-containing compound classes (carbazoles and pyridines, N class). For access the sulfur-containing compounds were employed the methylation reactions. As the increasing of distillation cut temperature, the amount of O2 compounds increased (from 9 for cut 2 to 66 for cut 12), and the average molecular weight distribution, M-w, shifted to higher m/z values (M-w = 169 -> 321 Da). These results were consistent with the increase of TAN with the boiling point. Plots of the DBE versus the carbon number for the O2 class of heavy distillation cuts (cuts 4-12) suggested a maximum abundance of the carbon numbers located at C-12-C-18 with a constant DBE of 3. For the nitrogen-containing compounds, 100 compounds were detected with m/z ranging from 160 to 414. Similar to O2 class, the amount of nitrogen species increased, and the M-w shifted for high values in function of distillation cut temperature: 6 species and M-w = 206 Da for cut 3; and 64 species and M-w = 340 Da for cut 12. The structures and the connectivity of naphthenic acids, phenols and pyridines were confirmed using ESI(+/-)-MS/MS. The most abundant sulfur compounds in heavy distillation cuts presented a carbon number of C-23 (for cut 11) and C-25 (for cut 12) with constant DBE of 3. Results of ESI(+/-)-FT-ICR MS contributed to the understanding of the chemical composition of Brazilian crude oil and the establishment of a correlation with the corrosion process. (C) 2013 Elsevier Ltd. All rights reserved.