| Individual component identification of compositionally complex and diverse petrochemicals presents a formidable challenge to modern analytical techniques. Most techniques lack the resolution and/or resolving power to identify individual components definitively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers ultra-high mass resolving power (m/Δm50% = 400,000) and high mass accuracy (better than 1 ppm) which enables molecular formula assignment to as many as 11,000+ peaks in a crude oil mass spectrum or as many as 30+ peaks at one nominal mass! In addition, the coupling of high field (9.4 T) FT-ICR MS to electrospray ionization (ESI) allows for selective ionization of polar compounds (S-, O-, and N-containing) within petrochemical samples. Based on the experimental behavior of model compounds, positive ion ESI was found to selectively ionize basic nitrogen compounds (e.g. pyridine homologues) while negative ion ESI was found to selectively ionize petroleum acids and neutral nitrogen compounds (e.g. pyrrole homologues). This selective ionization reduces the need for chromatographic fractionation of samples prior to analysis and, therefore, speeds analysis time.; In order for the identification of thousands of peaks in a petroleum sample to be feasible, timely, and provide useful information, a data reduction technique based on the Kendrick mass scale (where CH2 is 14.000 rather than 14.01565 Da) was used. Here compounds were identified as members of homologous series (namely, compounds with the same constitution of heteroatoms and number of rings plus double bonds, but different numbers of CH2 groups) instead of individually. Because members of a homologous series differ only by integer multiples of CH2, unequivocal assignment of a single member suffices to identify all of the other members. To further simply data analysis, we utilized a novel compact visual display which allows visual resolution of thousands of elemental compositions.; To date molecular formulas have been assigned to polar compounds in diesel, crude oils and asphaltenes (the hexane non-soluble fraction of crude oil) by use of positive and/or negative ion electrospray. Since molecular formula assignment brings knowledge of molecule aromaticity (rings plus double bonds) and carbon number distribution, petroleum chemists, engineers and geochemists gain an unprecedented level of molecular detail from FT-ICR MS data. |
