Identification of acidic NSO compounds in crude oils of different geochemical origins by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry Christine A. Hughey a,b , Ryan P. Rodgers a , Alan G. Marshall a,b, *, Kuangnan Qian c , Winston K. Robbins c a Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA b Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA c ExxonMobil Research and Engineering, 1545 Route 22 East, Annandale, NJ 08801, USA Received 30 October 2001; accepted 19 March 2002 (returned to author for revision 29 January 2002) Abstract We present the selective ionization, resolution and identification of acidic NSO compounds in three crude oils of different geochemical origins by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Selective ionization by ESI affords direct detection of neutral nitrogen compounds and carboxylic acids in petroleum without pre-chromatographic isolation. Ultra-high resolution/mass accuracy allows detailed and positive identification of acidic NSO compounds in the crude oils. Observed compositional differences reflect known crude oil properties/histories. Collectively,  14,000 masses, spanning 18 different heteroatomic classes, are identified unequivocally, demonstrating the potential of ESI-FT-ICR MS for geochemical applications. # 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction Polar compounds, such as N-, S-, O- and metal-con- taining compounds, make up a small portion of most crude oils (less than 15%) (Altgelt and Boduszynski, 1994) but have significant implications, both positive and negative, in petroleum exploration, production and refining. For example, asphaltene molecules (which are largely condensed aromatic compounds enriched in N, S and O) may precipitate from crudes and other heavy petroleum products and cause fouling during various stages of production (Joshi et al., 2001). During refining, sulfur compounds must be removed (often by hydro- treatment) to meet EPA standards. Sulfur removal, however, may be hindered by the presence of basic nitrogen compounds that deactivate hydrotreatment catalysts (La Vopa & Satterfield, 1988). Furthermore, nitrogen compounds contribute to fuel instability during storage (Chmielowiec et al., 1987; Worstell et al., 1981). Petroleum acids, another potential problem during refining, can cause liquid-phase corrosion (at elevated temperature) (Jayaraman and Saxena, 1995; Turnbull et al., 1998). On the positive side, heteroatomic compounds can provide useful geochemical clues that trace petroleum molecules back to their biological precursors. For example, phenols have been used to determine the origin of deposited organic matter (e.g. terrigenous or marine) (Fernandes et al., 1999). Naphthenic acids, when pre- sent at low concentration, serve as geochemical fossils of the original source rock and indicators of crude oil maturity (Jaffe´ and Gardinali, 1990; Mackenzie et al., 0146-6380/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(02)00038-4 Organic Geochemistry 33 (2002) 743–759 www.elsevier.com/locate/orggeochem * Corresponding author. Tel.: +1-850-644-0529; fax: +1-850- 644-1336. E-mail address: marshall@magnet.fsu.edu (A.G. Marshall).