Mass Resolving Power Requirement for Molecular Formula Determination of Fossil Oils

Ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been demonstrated to be capable of resolving doublets with mass difference of an electron. However, this resolving power can still be insufficient for positively identifying all of the overlapping species in petroleum and other fossil oils. To look into the ultimate resolving power required, we investigated all possible overlaps in molecular masses of monoisotopic, ¹³C- and ³⁴S-containing hydrocarbon and heterocompound species that are commonly found in petroleum. Among homologous series containing up to 3 heteroatoms and with up to 30 double bond equivalences, it was found that over 80% even-mass and 50% odd-mass series have overlapping series with mass differences less than an electron mass of 0.458 mDa (458 μDa). Previously introduced nominal mass series are recommended to use as additional means of differentiating the overlapping series. However, the ultimate resolving power required for resolving all possible overlaps is 0.1 mDa, less than the mass of an electron. This should be one of the goals for developing future mass spectrometers with higher resolving power

Algae Polar Lipids Characterized by Online Liquid Chromatography Coupled with Hybrid Linear Quadrupole Ion Trap/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We report the first application of online LC-MS (liquid chromatography–mass spectrometry) characterization of algae polar lipids by nanoscale high-performance liquid chromatography followed by electrospray ionization and mass analysis with a linear ion trap (LTQ) coupled with 14.5 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Ultrahigh FT-ICR mass resolution provides highly accurate mass measurement and resolves monoisotopic peaks from interfering components for unique determination of lipid elemental compositions. We establish the polar lipid profile of fatty acids, glycolipids, phospholipids, and betaine lipids for a green algae, <i>Nannochloropsis oculata</i>, which is highly prized for its oils suitable for biodiesel production. Lipid headgroup and fatty acid identification is based on accurate mass measured by the FT-ICR MS and collision-induced dissociation (CID) MS/MS in the LTQ. Unequivocal lipid composition is further confirmed from isotopic fine structure at baseline resolutionachievable only with ultrahigh resolution FT-ICR MS

Characterization of Acidic Compounds in Heavy Petroleum Resid by Fractionation and Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Analysis

Negative-ion electrospray ionization (ESI) enabled the direct mass spectrographic analysis of phenols, naphthenic acids, and neutral nitrogen compounds in petroleum fractions without prefractionation; however, ESI results provide few quantitative and structural information about the analytes: the composition of acidic compounds in heavy oil, such as distillate resid, is still unclear. In this study, extrography was used to fractionate oilsands bitumen-derived vacuum-topped bitumen (VTB) and its maltene and asphaltene fractions into multiple subfractions. The molecular compositions of acidic functional compounds in the VTB and its subfractions were analyzed by negative-ion ESI Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Extrographic separation was a necessary step to isolate acidic compounds of various acidities and/or polarities in vacuum resid fractions to achieve a systematic analysis. The results showed that the O₂ class species in VTB were highly condensed phenols and carboxylic acids. The maltene fraction contained most of the less condensed naphthenic acids, whereas the asphaltene fraction contained highly condensed carboxylic acids and phenolic compounds with a bouble-bond equivalent (DBE) higher than 6. The presence of acids had no significant impact on the yield of asphaltenes in <i>n</i>-C₇ solvent precipitation. Acid-free asphaltene fractions, which account for more than 90 wt % of the asphaltenes, cannot be ionized by negative-ion ESI

Characterization of Middle-Temperature Gasification Coal Tar. Part 3: Molecular Composition of Acidic Compounds

Coal tar has been considered as a potential energy alternative because of dwindling supplies of petroleum. To determine if the coal tar could be refined and upgraded to produce clean transportation fuels, detailed investigation of its composition is necessary, particularly for identifying the acidic components that account for about one-quarter of the weight of the coal tar. A middle-temperature coal tar (MTCT) and its fractions were characterized by gas chromatography–mass spectrometry (GC–MS) and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with different ion transmission modes for high- and low-mass ions. Analytical results of narrow distillation fractions from FT-ICR MS agreed reasonably well with those from GC–MS, although each technique has its own advantages and disadvantages. In this work, FT-ICR MS was demonstrated to be capable of characterizing small molecules of <100 Da using appropriate operation conditions, thus yielding mass distributions to compare to GC–MS results. A continuous distribution in double bond equivalent (DBE) and carbon number was observed with the distillates of increasing boiling point, while the composition of the distillation residue was much more complex than that of distillates. Acidic compounds containing 1–7 oxygen atoms were observed in the MTCT by FT-ICR MS, with O₁ and O₂ classes being dominant. Various phenolic compounds with 1–4 aromatic rings were identified on the basis of literature references, including some molecules having structures resembling known biomarkers in petroleum and coal