From mass to structure: an aromaticity index for high‐resolution mass data of natural organic matter

Recent progress in Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) provided extensive molecular mass data for complex natural organic matter (NOM). Structural information can be deduced solely from the molecular masses for ions with extreme molecular element ratios, in particular low H/C ratios, which are abundant in thermally altered NOM (e.g. black carbon). In this communication we propose a general aromaticity index (AI) and two threshold values as unequivocal criteria for the existence of either aromatic (AI > 0.5) or condensed aromatic structures (AI >= 0.67) in NOM. AI can be calculated from molecular formulae which are derived from exact molecular masses of naturally occurring compounds containing C, H, O, N, S and P and is especially applicable for substances with aromatic cores and few alkylations. In order to test the validity of our model index, AI is applied to FTICRMS data of a NOM deep-water sample from the Weddell Sea (Antarctica), a fulvic acid standard and an artificial dataset of all theoretically possible molecular formulae. For graphical evaluation a ternary plot is suggested for four-dimensional data representation. The proposed aromaticity index is a step towards structural identification of NOM and the molecular identification of black carbon in the environment.

[1]  Gerhard Kattner,et al.  Molecular formulae of marine and terrigenous dissolved organic matter detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry , 2005 .

[2]  Sunghwan Kim,et al.  Hydrogen Deficient Molecules in Natural Riverine Water Samples - Evidence for the Existence of Black Carbon in DOM , 2004 .

[3]  M. Simpson,et al.  Determination of black carbon in natural organic matter by chemical oxidation and solid-state 13C nuclear magnetic resonance spectroscopy , 2004 .

[4]  M. Simpson,et al.  Overestimates of black carbon in soils and sediments , 2004, Naturwissenschaften.

[5]  P. Hatcher,et al.  Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry. , 2004, Environmental science & technology.

[6]  Sunghwan Kim,et al.  Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the van Krevelen diagram. , 2003, Analytical chemistry.

[7]  A. Marshall,et al.  Exact masses and chemical formulas of individual Suwannee River fulvic acids from ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectra. , 2003, Analytical chemistry.

[8]  A. Marshall,et al.  Ionization and fragmentation of humic substances in electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry. , 2002, Analytical chemistry.

[9]  Michael A. Freitas,et al.  The application of electrospray ionization mass spectrometry (ESI MS) to the structural characterization of natural organic matter , 2002 .

[10]  Michael A. Freitas,et al.  High-resolution Fourier transform ion cyclotron resonance mass spectrometry of humic and fulvic acids: improvements and comparisons. , 2002, Analytical chemistry.

[11]  Dennis A. Hansell,et al.  Biogeochemistry of marine dissolved organic matter , 2002 .

[12]  Lu Xu,et al.  Developing Molecular Identification Numbers by an All-Paths Method , 1997, J. Chem. Inf. Comput. Sci..

[13]  A. Kerber,et al.  MOLGEN+, a generator of connectivity isomers and stereoisomers for molecular structure elucidation , 1995 .

[14]  E. Druffel,et al.  Radiocarbon in dissolved organic matter in the central North Pacific Ocean , 1987, Nature.

[15]  Robert W. Robinson,et al.  The numbers of chiral and achiral alkanes and monosubstituted alkanes , 1976 .