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

Abstract

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.

Interactive van Krevelen diagrams – Advanced visualisation of mass spectrometry data of complex mixtures

“…Likewise, there exist a number of well‐studied complex mixtures, including natural organic matter (NOM), i.e. dissolved organic matter,5, 10, 11 soil organic matter,12 and organic aerosols,13, 14, 15 petroleum,16, 17 or beverages such as wine18 or Scotch whisky 19, 20. Amongst the most complex of these, a component of NOM and the closest sample to a universal standard, is Suwannee River Fulvic Acid (SRFA) produced by the International Humic Substance Society 21.…”

The importance of both charge exchange and proton transfer in the analysis of polycyclic aromatic compounds using atmospheric pressure chemical ionization mass spectrometry

“…Hence, the determination of PACs has been of great interest for many years, but complete, detailed analyses have been hampered by complex matrices, trace level concentrations, a large number of isomers, many similar compounds and a lack of reference standards. Special methods of analysis beyond classical procedures include multidimensional chromatographic separations with mass spectrometric detection, high resolution mass spectrometry and atmospheric pressure mass spectrometric methods [1][2][3][4]. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is an important technique when interfacing mass spectrometry to high-performance liquid chromatography (HPLC) for the analysis of PACcontaining samples.…”

Shifting unoccupied spectral space in mass spectrum of peptide fragment ions

“…Mass defects of theoretical fragment ions from native and modified peptides were converted to averagine-scale mass defects. The conversion of IUPAC exact mass (EM IUPAC ), nominal mass (NM IUPAC , the round value of EM IUPAC ), and mass defect (MD IUPAC ) of peptide ions to those on the averagine scale was performed using equations described in a previous paper [9], which followed earlier equations used for studying ion mass defect [24,25]. Ion frequency for a defined range of the averagine-scale mass defect (bin size ϭ 0.0075 u*) was plotted against the averagine-scale mass defect of fragment ions.…”

“…The scaling conversion of the peptide ion mass from the IUPAC scale ( 12 C ϭ 12 u as the mass reference) to the averagine scale (averagine mass ϭ 111 u* as the mass reference with zero mass defect; u*: the mass unit on the averagine scale) uses a scaling factor of 0.999493894 (ϭ 111/111.0543052) [9]. The mass defect of an ion on the averagine scale (MD Avg ) was defined to be the difference between the nominal mass of the ion and its exact mass on the averagine scale, following similar equations used by others previously [24,25].…”

“…Averagine-scale mass defects for amino acid residues were plotted against their nominal masses (Figure 2) to establish a mass defect plot [24,25] on the averagine scale [9]. Amino acid residues distributed about evenly at both sides of the zero MD Avg line (blue dotted line in Figure 2).…”