Resolution, elemental composition, and simultaneous monitoring by Fourier transform ion cyclotron resonance mass spectrometry of organosulfur species before and after diesel fuel processing

Elemental compositional analysis of processed and unprocessed diesel fuels is obtained with a 5.6-T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer coupled to an all-glass heated, inlet system (AGHIS). High-resolution mass spectra of electron-ionized diesel fuel samples are obtained from as little as a 500-nL septum injection into the AGHIS, to yield similar to 500 peaks over a range 90 < m/z < 300, with as many as seven peaks present at the same nominal mass. Molecular formulas (elemental compositions) are assigned from accurate mass measurement with an average error less than +/- 0.5 ppm. Comparison of the raw and processed diesel spectra shows complete removal of the sulfur-containing species except for dimethyldibenzothiophene and higher alkyl-substituted dibenzothiophenes. These results confirm prior reports of the resistance of these Species to hydrotreatment due to steric hindrance of catalytic desulfurization arising from 4,6 dimethyl substitution.. A simple liquid chromatographic separation to isolate N-, O-, and S-containing aromatics from processed diesel fuel simplifies the mass spectrum and extends the dynamic range of the analysis, making it possible to identify many nitrogen and oxygen homologues of the sulfur-containing species, as well as to confirm the presence of sulfur-containing species initially detected in the unfractionated processed diesel fuel.