The Characterization of Basic Petroleum Extracts by High-Resolution Mass Spectrometry and Simultaneous Orthogonal Acceleration Time-of-Flight−Magnet Scanning Tandem Mass Spectrometry

Abstract

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 CnH2n+zN and CnH2n+zNS 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.