Kendrick Mass Defect Spectrum:  A Compact Visual Analysis for Ultrahigh-Resolution Broadband Mass Spectra

• Published in: Analytical chemistry (Washington) Vol. 73; no. 19; pp. 4676 - 4681
• Main Authors: Hughey, Christine A, Hendrickson, Christopher L, Rodgers, Ryan P, Marshall, Alan G, Qian, Kuangnan
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.10.2001
• Subjects: Analytical chemistry; Applied sciences; Chemistry; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Ions; Scientific imaging; Spectrometric and optical methods; Spectrum analysis; Oil industry; Petroleum fraction; Chemical analysis; Multicomponent analysis; Molecular weight distribution; Molecular weight determination; Qualitative analysis; Ion cyclotron resonance; Mass spectrometry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac010560w

At currently achievable Fourier transform ion cyclotron resonance broadband mass spectrometry resolving power (m/ Δ m 50% > 350 000 for 200 < m/z < 1000), it would be necessary to spread out a conventional mass spectrum over ∼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°, 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., ∼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; ∼2-Da separations, corresponding to a double bond or ring; ∼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 (N n O o S s ), type (Z in C c H2 c + Z N n O o S s ), and alkylation seriesmay be identified visually as well.