5564 r2009 American Chemical Society pubs.acs.org/EF Energy Fuels 2009, 23, 5564–5570 : DOI:10.1021/ef9006005 Published on Web 09/16/2009 Analysis of Asphaltenes and Asphaltene Model Compounds by Laser-Induced Acoustic Desorption/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry David S. Pinkston, † Penggao Duan, †,^ Vanessa A. Gallardo, † Steven C. Habicht, † Xiaoli Tan, § Kuangnan Qian, ‡ Murray Gray, § Klaus Mullen, ) and Hilkka I. Kentta¨ maa* ,† † Department of Chemistry, Purdue University, 560 Oval Dr., West Lafayette, Indiana 47907, ‡ ExxonMobil Research and Engineering Company, 1545 Route 22 East, Annandale, New Jersey 08801, § Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada, ) Max Planck Institute fur Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany, and ^ Current address: Bruker Daltonics Inc. 40 Manning Rd., Billerica, Massachusetts 01821 Received June 12, 2009. Revised Manuscript Received August 21, 2009 Laser-induced acoustic desorption (LIAD)/electron ionization (EI) was used to study asphaltene model compounds and asphaltenes derived from North American crude oil in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer (MS). Successful desorption by LIAD of all model compounds (including a polyphenylated vanadoyl porphyrin) as intact neutral molecules into the mass spectrometer indicates that this method allows the evaporation of most if not all components of asphaltenes into mass spectrometers for further characterization. Electron ionization is a universal ionization method that ionizes all organic compounds. Hence, it is not surprising that all the model compounds studied were successfully ionized by using this method. Furthermore, this method yielded stable molecular ions for all model compounds studied. Because LIAD/EIMS provides MW information for these model compounds, this is almost certainly also true for all components of asphaltenes. Examination of asphaltene samples derived from North American crude oil by using this technique yielded a MW distribution of about 350-1050 Da and provided structural information for asphaltene components. Introduction Asphaltenes are typically defined as a petroleum fraction soluble in toluene and insoluble in n-heptane. 1 They are known as the heaviest components with the highest boiling points in crude oil. They have a high degree of aromaticity and can contain nitrogen, oxygen, sulfur, and metal atoms. Re- moval of contaminants in asphaltenes during the processing of crude oil is necessary to avoid catalyst fouling and hence lower liquid yields. 2-5 Also, asphaltenes can precipitate in the equipment, thus increasing maintenance costs. 5 Hence, the achievement of a better understanding of asphaltenes’ composition has become important. 6-8 Furthermore, in the years to come, the significance of asphaltenes is poised to increase as oil industry shifts to the use of heavier crude oils that contain high concentrations (∼15%) of asphaltenes. 9 A deeper understanding of asphaltenes is required to effec- tively utilize these resources. The analysis of asphaltenes has proven to be a challenging endeavor due to their molecular complexity, high boiling points, limited solubility, and tendency to aggregate. Thus, the molecular compositions of asphaltenes remain poorly understood. Many studies have been dedicated just to probing the molecular weight (MW) distributions of asphaltenes. 10-12 However, contradictory results have sparked a controversy over the correct distributions. The reported MW distributions of petroleum asphaltenes span from a low mass distribution with a range of about 400-1500 Da to high mass distributions that extend past 10 6 Da. Several recent reviews focus on this controversial topic. 13-15 Time-resolved fluorescence depolarization (TRFD) was the technique that first provided evidence in support of a “low” mass distribution for asphaltenes. 16-18 Moreover, this tech- nique provided evidence for an “island” (one aromatic core) molecular model of asphaltenes rather than the “archipelago” *To whom correspondence should be addressed. E-mail: hilkka@ purdue.edu. (1) Mullins, O. C.; Sheu, E. Y.; Hammami, A.; Marshall, A. G., Asphaltenes, Heavy Oils, and Petroleomics; Springer: New York, 2007. 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