Technical Notes Microchip Atmospheric Pressure Photoionization for Analysis of Petroleum by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Markus Haapala, † Jeremiah M. Purcell, ‡ Ville Saarela, | Sami Franssila, | Ryan P. Rodgers, ‡,§ Christopher L. Hendrickson, ‡,§ Tapio Kotiaho, †,⊥ Alan G. Marshall,* ,‡,§ and Risto Kostiainen* ,† Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, P.O. Box 56, FI-00014 Helsinki, Finland, Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310-4005, Microfabrication Group, Department of Micro and Nanosciences, Helsinki University of Technology, P.O. Box 3500, FI-02015 TKK, Finland, and Laboratory of Analytical Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland Atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT- ICR MS) has significantly contributed to the molecular speciation of petroleum. However, a typical APPI source operates at 50 μL/min flow rate and thus causes a considerable mass load to the mass spectrometer. The recently introduced microchip APPI (μAPPI) operates at much lower flow rates (0.05-10 μL/min) providing decreased mass load and therefore decreased contamina- tion in analysis of petroleum by FT-ICR MS. In spite of the 25 times lower flow rate, the signal response with μAPPI was only 40% lower than with a conventional APPI source. It was also shown that μAPPI provides very efficient vaporization of higher molecular weight compo- nents in petroleum analysis. The characterization of petroleum components is highly important in development and selection of refining processes. Petroleum is a complex matrix with over 100 000 different compounds covering polar and nonpolar compounds and mass range from 100 Da to over 1000 Da. Thus, the analysis of petroleum is challenging and requires highly advanced analytical techniques. Gas chromatography/mass spectrometry is a widely used technique in analysis of volatile and semivolatile compounds in petroleum. 1 However, gas chromatography is not suitable for higher-boiling point compounds, and other techniques such as high-resolution mass spectrometry combined with various ioniza- tion methods have been successfully applied to analysis of petroleum components. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is the most efficient and commonly used mass spectrometric method for detailed compositional studies of complex petroleum samples without sample pretreatment or chromatographic separation. This is achieved due to the high mass resolution and accuracy of FT- ICR MS, which allows confident assignment of elemental com- position to thousands of peaks. 2 During the past few years the analysis of crude oil and its components by FT-ICR MS has emerged as a new area of high-performance chemical analysis named “petroleomics”. 3-10 Several ionization techniques have been applied for ionization of petroleum components. Commonly used electrospray ionization (ESI) is selective toward the ionization of polar heteroatomic molecules (mostly basic and acidic compounds). Field desorption/ field ionization, 11,12 matrix-assisted laser desorption ionization, 13,14 * To whom correspondence should be addressed. E-mail: risto.kostiainen@ helsinki.fi (R.K.); marshall@magnet.fsu.edu (A.G.M.). Phone: 358-9-191 59 134 (R.K.); 1-850-644-0529 (A.G.M.). Fax: 358-9-191 59 556 (R.K.); 1-850-644-1366 (A.G.M.). † Faculty of Pharmacy, University of Helsinki. ‡ Florida State University. § National High Magnetic Field Laboratory. | Helsinki University of Technology. ⊥ Department of Chemistry, University of Helsinki. (1) Wang, Z. D.; Fingas, M. J. Chromatogr., A 1997, 774, 51–78. (2) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G. Anal. Chem. 2002, 74, 4145– 4149. (3) Marshall, A. G.; Rodgers, R. P. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 18090–18095. (4) Miyabayashi, K.; Naito, Y.; Tsujimoto, K.; Miyake, M. Int. J. Mass Spectrom. 2002, 221, 93–105. (5) Hughey, C. A.; Galasso, S. A.; Zumberge, J. E. Fuel 2007, 86, 758–768. (6) Pakarinen, J. M. H.; Teravainen, M. J.; Pirskanen, A.; Wickstrom, K.; Vainiotalo, P. Energy Fuels 2007, 21, 3369–3374. (7) Schrader, W.; Panda, S. K.; Brockmann, K. J.; Benter, T. Analyst 2008, 133, 867–869. (8) Panda, S. K.; Schrader, W.; Andersson, J. T. Anal. Bioanal. Chem. 2008, 392, 839–848. 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