The ability of electrospray ionization mass spectrometry (ESI MS) to analyze heavy aromatic petroleum fractions using silver nitrate as a reagent compound to form characteristic adduct ions has been examined. The complexation of aromatic compounds containing long alkyl substituents with the silver ion leads to the formation of abundant adduct ions such as [M + Ag]+ and [2M + Ag]+. The concentration of the [2M + Ag]+ ions can be reduced by increasing the sampling cone voltage. Molecular ions and other adduct ions may also be formed depending on the structure of the aromatic molecule. Results obtained from the analysis of representative heavy petroleum fractions and vacuum residues by the Ag+ ESI MS method and conventional ionization methods were in good agreement. The current method extends the applicability of electrospray ionization to the analysis of neutral hydrocarbons in heavy aromatic petroleum fractions. It is simple and compatible with widely available LC/MS instrumentation. The extreme complexity of the Ag

A method has been developed for the reduction of the chemical formulas of compounds in complex mixtures from the isotopic peak distributions of high-resolution mass spectra. The method is based on the principle that the observed isotopic peak distribution of a mixture of compounds is a linear combination of the isotopic peak distributions of the individual compounds in the mixture. All possible chemical formulas that meet specific criteria (e.g., type and number of atoms in structure, limits of unsaturation, etc.) are enumerated, and theoretical isotopic peak distributions are generated for each formula. The relative amount of each formula is obtained from the accurately measured isotopic peak distribution and the calculated isotopic peak distributions of all candidate formulas. The formulas of compounds in simple spectra, where peak components are fully resolved, are rapidly determined by direct comparison of the calculated and experimental isotopic peak distributions. The singular value decomposition linear algebra method is used to determine the contributions of compounds in complex spectra containing unresolved peak components. The principles of the approach and typical application examples are presented. The method is most useful for the characterization of complex spectra containing partially resolved peaks and structures with multiisotopic elements.

This work explores the possibility of Ag+ electrospray ionization mass spectrometry (ESI-MS) to determine the molecular weight distributions of non-boiling petroleum fractions. Information about the molecular weight distributions is needed for fundamental studies on the nature of heavy crude oils and bitumens and for the development of novel recovery and processing methods. The method does not depend on thermal processes for the introduction of the fractions into the gas phase of the mass spectrometer, which is a considerable advantage over most other ionization methods. The Ag+ electrospray mass spectra of the fractions analyzed by using a toluene/methanol/cyclohexane (60:28:12%) solvent system display bimodal distributions in the ranges m/z approximately 300 to approximately 3000 and m/z 3000 to approximately 20,000. The abundances of the high molecular weight peak distributions can be reduced by in-source collisional activation experiments. Comparisons with the results obtained for model heteroatom-containing compounds (molecular weight < 600 Da) and high molecular weight polystyrene standards (up to one million Da) indicate that the majority of the structures in the saturate, naphthenoaromatic and polar aromatic fractions, and a significant portion of the asphaltenes, are small molecules. However, a considerable portion of the asphaltenes and some portion of the other fractions contain high molecular weight structures bound by covalent or strong non-covalent bonds. The results obtained by the Ag+ ESI method in this study for the saturate, aromatic, and polar fractions in a bitumen are in qualitative agreement with published molecular weight average results obtained for Cold Lake bitumen fractions analyzed by conventional gel permeation chromatography and field desorption mass spectrometry. Further work is needed to study the nature of the bonds and the interactions of the molecules in the asphaltene fractions by Ag+ ESI-MS.

A hybrid double-focusing high-resolution magnetic sector−orthogonal acceleration time-of-flight (oa-TOF) tandem mass spectrometer has been used for the characterization of the basic compounds in a whole crude oil and its 400−414 °C distillation cut. Detailed compositional characterization is obtained from high-resolution experiments. Structural information is obtained from automated magnet scanning mass spectroscopy (MS/MS) experiments that are conducted by continuous oa-TOF data acquisition and simultaneous scanning of the magnet. Solid-phase weak cation exchange is used to remove the basic compounds from the hydrocarbon matrix. Samples are introduced into the mass spectrometer via a dynamic batch inlet system. Molecular ions are produced by charge exchange chemical ionization. The most-abundant compounds in the two basic extracts are due to the C n H2 n + z N and C n H2 n + z NS compound classes. Other compound classes of lower concentration are also detected (−NO, −SON, −NO2, −O, −SO, −O2, −SO2). The contour plot of the MS/MS data for the 400−414 °C extract has revealed two characteristic peak patterns:  (i) a series of peaks parallel to the precursor ion series, containing information about the degree of alkyl substitution, and (ii) a series of peaks parallel to the MS-1 axis containing information about the aromatic nuclei. Despite the complexity of the data, a substantial structural similarity between the various basic nitrogen compounds is indicated by the two peak patterns. The important capability of the simultaneous MS/MS method to provide structural information about isobaric peak components is demonstrated. The chemical formulas of selected isobaric precursor ions are validated, and structures consistent with their product ion spectra are proposed.

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