Ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry has resolved and identified the elemental compositions of over 10000 organic constituents of coal and petroleum crude oil. A plot of Kendrick mass defect versus Kendrick nominal mass sorts compounds into homologous series according to compound class (i.e., numbers of N, O, and S heteroatoms), type (number of rings plus double bonds), and degree of alkylation (number of CH(2) groups), to yield unique elemental assignments from ultrahigh-resolution mass measurements in the 200-900 Da range. Interpretation of such a vast compilation requires a simple (preferably graphical) means to differentiate between complex organic mixtures of different origin or processing. In an extension of the recently revived van Krevelen plot, each elemental composition is projected onto two or three axes according to its H/C, O/C, and/or N/C atomic ratios. The H/C ratio separates compounds according to degree of saturation, whereas O/C or N/C ratios separate according to O and N classes. We show that the three-dimensional van Krevelen diagram can completely separate different classes in pyridine-extracted coal or petroleum samples and can also graphically distinguish fossil fuels according to their nature (coal vs petroleum), maturation (coals of different rank), and processing (the same coal at two stages of liquefaction). The van Krevelen diagram thus appears well suited to amplifying and exposing compositional differences within and between complex organic mixtures.
Coal is one of the world's most chemically complex natural mixtures, whose composition varies with origin and age. Its combustion yields environmentally relevant "greenhouse" gases such as SO X and NO X . Here, for the first time, we apply electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to the analysis of Illinois No. 6 and Pocahontas No. 3 pyridine coal extracts. With the aid of Kendrick mass scaling, the elemental compositions can be sorted into different homologous series according to compound "class" (number of various heteroatoms) and "type" (rings plus double bonds). Many more species and classes were detected in Illinois No. 6 coal than in Pocahontas No. 3 coal. Illinois No. 6 coal contains mainly oxygen-and sulfur-containing classes; conversely, Pocahontas No. 3 coal contains nitrogencontaining classes. Both coals share O 2 and NO 2 classes. Pocahontas coal exhibits much greater aromaticity (more rings plus double bonds) and less alkyl substitution (lower carbon number distribution) than Illinois No. 6, in accord with prior evidence that Pocahontas coal has higher carbon content (therefore higher rank) than Illinois No. 6 coal. Both the compositional information and the aromaticity data correlate well with known compositional and geochemical information.
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