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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