Resolution and Identification of Elemental Compositions for More than 3000 Crude Acids in Heavy Petroleum by Negative-Ion Microelectrospray High-Field Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

• Published in: Energy & fuels Vol. 15; no. 6; pp. 1505 - 1511
• Main Authors: Qian, Kuangnan, Robbins, Winston K, Hughey, Christine A, Cooper, Helen J, Rodgers, Ryan P, Marshall, Alan G
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.2001
• Subjects: Applied sciences; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Sulfur heterocycle; Molecular structure; Carboxylic acid; Crude oil; Chemical composition; Ion cyclotron resonance spectrometry; Polycyclic aromatic compound; Mass spectrometry; Electrospray; Heavy oil
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef010111z

Although crude acids are minor constituents in petroleum, they have significant implications for crude oil geochemistry, corrosion, and commerce. We have previously demonstrated that a single positive-ion electrospray ionization (ESI) high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) experiment can resolve and identify 3000 chemically different elemental compositions of bases (basic nitrogen compounds) in a crude oil. Here, we show that negative-ion ESI high-field FT-ICR MS can selectively ionize and identify naphthenic acids without interference from the hydrocarbon background. When combined with prechromatographic separation, ESI FT-ICR MS reveals an even more detailed acid composition. An average mass resolving power, m/Δm 50% ≥ 80 000 (Δm 50% is mass spectral peak full width at half-maximum peak height) across a wide mass range (200 < m/z < 1000), distinguishes as many as 15 distinct chemical formulas within a 0.26 Da mass window. Collectively, more than 3000 chemically different elemental compositions containing O2, O3, O4, and O2S, O3S, and O4S were determined in a South American heavy crude. Our data indicates that the crude acids consist of a mixture of structures ranging from C15−C55 with cyclic (1−6 rings) and aromatic (1−3 ring) structures. The acid composition appears to be simpler than that of the corresponding hydrocarbon analogues.