Elemental composition analysis of processed and unprocessed diesel fuel byelectrospray ionization fourier transform ion cyclotron resonance mass spectrometry

High-resolution (100 000 < M/Deltam(50%) < 250 000, in which Deltam(50%) de notes mass spectral peak fall width at half-maximum height) electrospray io nization Fourier transform ion cyclotron resonance positive-ion mass spectr a of unprocessed (and processed) diesel fuels resolves approximately 500 (a nd 200) chemically different constituents over a mass range from 200 to 452 Da, with as many as 6 resolved elemental compositions at a given nominal m ass. Molecular formulas were assigned from accurate mass measurement to wit hin +/-1 ppm. Compound types were identified by Kendrick mass analysis. On the basis of the experimental behavior of model compounds, electrospray ion ization was found to ionize selectively basic pyridine homologues-compounds responsible for deactivation of hydrotreatment catalysts and instability o f fuels during storage. Compound classes identified in the unprocessed dies el fuel include those containing N, N-2, NS, NO, N2O, O-2, and SO and, in t he processed diesel, N, N-2, NO2, and SO. Comparison of unprocessed and pro cessed diesel fuel reveals that N- and N-2-type compounds are resistant to laboratory hydrotreatment. In contrast, NS-, NO-, N2O-, and O-2-containing compounds were completely removed by hydrotreatment. Concentration-dependen t dimers observed above 450 Da were confirmed by infrared multiphoton disso ciation.