At currently achievable Fourier transform ion cyclotron resonance broadband mass spectrometry resolving power (m/deltam50% > 350,000 for 200 < m/z < 1,000), it would be necessary to spread out a conventional mass spectrum over approximately 200 m in order to provide visual resolution of the most closely resolved peaks. Fortunately, there are natural gaps in a typical mass spectrum, spaced 1 Da apart, because virtually no commonly encountered elemental compositions yield masses at those values. Thus, it is possible to break a broadband mass spectrum into 1-Da segments, rotate each segment by 90 degrees, scale each segment according to its mass defect (i.e., difference between exact and nominal mass), and then compress the spacing between the segments to yield a compact display. For hydrocarbon systems, conversion from IUPAC mass to "Kendrick" mass (i.e., multiplying each mass by 14.00000/14.01565) further simplifies the display by rectilinearizing the peak patterns. The resulting display preserves not only the "coarse" spacings (e.g., approximately 1 Da between odd and even masses, corresponding to either even vs odd number of nitrogens or 12C(c) vs 12C(c-1)13C1 elemental compositions of the same molecule; approximately 2-Da separations, corresponding to a double bond or ring; approximately 14 Da separations, corresponding to one CH2 group) but also the "fine structure" (i.e., different mass defects for different elemental compositions) across each 1-Da segment. The method is illustrated for experimental electrospray ionization FTICR ultrahigh-resolution mass spectra of a petroleum crude oil. Several thousand elemental compositions may be resolved visually in a single one-page two-dimensional display, and various compound families-class (NnOoSs), type (Z in C(c)H2(c+z)NnOoSs), and alkylation series-may be identified visually as well.

Although crude acids are minor constituents in petroleum, they have significant implications for crude oil geochemistry, corrosion, and commerce. We have previously demonstrated that a single positive-ion electrospray ionization (ESI) high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) experiment can resolve and identify 3000 chemically different elemental compositions of bases (basic nitrogen compounds) in a crude oil. Here, we show that negative-ion ESI high-field FT-ICR MS can selectively ionize and identify naphthenic acids without interference from the hydrocarbon background. When combined with prechromatographic separation, ESI FT-ICR MS reveals an even more detailed acid composition. An average mass resolving power, m/∆m 50% g 80 000 (∆m 50% is mass spectral peak full width at half-maximum peak height) across a wide mass range (200 < m/z < 1000), distinguishes as many as 15 distinct chemical formulas within a 0.26 Da mass window. Collectively, more than 3000 chemically different elemental compositions containing O 2 , O 3 , O 4 , and O 2 S, O 3 S, and O 4 S were determined in a South American heavy crude. Our data indicates that the crude acids consist of a mixture of structures ranging from C 15 -C 55 with cyclic (1-6 rings) and aromatic (1-3 ring) structures. The acid composition appears to be simpler than that of the corresponding hydrocarbon analogues.

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Extra heavy petroleum crude oil (50% of the mixture boils at >566 °C) has been analyzed directly, without prior fractionation, by a high-field (9.4 T) Fourier transform ion cyclotron resonance mass spectrometer coupled to an external micro-electrospray ion source. At an average mass resolving power, (m/Δm 50% ≈ 50 000), a single wideband (250−1250 Da) mass spectrum exhibited ∼5000 resolved peaks with an average mass of 617 Da (e.g., up to 7−10 resolved peaks at each nominal mass). Their elemental compositions were positively identified by accurate mass measurement with an average deviation of less than 1 mDa from each assigned elemental composition. The number of elemental compositions at each nominal mass, the number of sulfur/oxygen atoms in a molecule, and aromaticity each increase with increasing mass. On the basis of elemental composition alone, we resolve more than 3000 distinct chemical formulas (excluding 13C isotopic species). Of the 3000 unique elemental compositions, we identify 12 major heteroatomic “classes”; (e.g., molecules containing N, NS, NS2, NO, NOS, etc.); for the various “classes”, we identify more than 100 hydrocarbon “types” (e.g., molecules with the same number of rings plus double bonds); and for each “type”, we determine the carbon number distribution (20−80 carbons) to reveal the number of alkyl carbons appended to aromatic rings. The present results represent the most complete chemical characterization ever achieved for such a complex mixture, based on a single experimental data set.

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