A New Matrix Assisted Ionization Method for the Analysis of Volatile and Nonvolatile Compounds by Atmospheric Probe Mass
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J. Am. Soc. Mass Spectrom. (2013) 24:1102Y1107 DOI: 10.1007/s13361-013-0634-9
RESEARCH ARTICLE
A New Matrix Assisted Ionization Method for the Analysis of Volatile and Nonvolatile Compounds by Atmospheric Probe Mass Spectrometry Shubhashis Chakrabarty,1 Vincent S. Pagnotti,1 Ellen D. Inutan,2 Sarah Trimpin,2 Charles N. McEwen1 1 2
University of the Sciences, Philadelphia, PA, USA Wayne State University, Detroit, MI, USA
Abstract. Matrix assisted ionization of nonvolatile compounds is shown not to be limited to vacuum conditions and does not require a laser. Simply placing a solution of analyte dissolved with a suitable matrix such as 3-nitrobenzonitrile (3-NBN) or 2,5-dihydroxyacetophenone on a melting point tube and gently heating the MS ASAP dried sample near the ion entrance aperture of a mass spectrometer using a flow of Probe gas produces abundant ions of peptides, small proteins, drugs, and polar lipids. Fundamental studies point to matrix-mediated ionization occurring prior to the entrance aperture of the mass spectrometer. The method is analytically useful, producing peptide mass fingerprints of bovine serum albumin tryptic digest consuming sub-picomoles of sample. Application of 100 fmol of angiotensin I in 3-NBN matrix produces the doubly and triply protonated molecular ions as the most abundant peaks in the mass spectrum. No carryover is observed for samples containing up to 100 pmol of this peptide. A commercial atmospheric samples analysis probe provides a simple method for sample introduction to an atmospheric pressure ion source for analysis of volatile and nonvolatile compounds without using the corona discharge but using sample preparation similar to matrix-assisted laser desorption/ionization. Key words: Nonvolatile compounds, Peptides, Drugs, Lipids, Mass spectrometry, Matrix assisted, Probe introduction NO2
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Received: 19 February 2013/Revised: 27 March 2013/Accepted: 28 March 2013/Published online: 10 May 2013
Introduction
T
here are a number of ways to directly ionize compounds that can be vaporized in vacuum, including solid probe electron and chemical ionization mass spectrometry (MS) [1], and from atmospheric pressure (AP) using, for example, direct analysis in real time (DART) [2], atmospheric sample analysis probe (ASAP) [3], and most recently, Leidenfrost phenomenon thermal desorption (LPTD) [4] methods. Direct analysis of nonvolatile compounds is most commonly
Shubhashis Chakrabarty and Vincent S. Pagnotti contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s13361-013-0634-9) contains supplementary material, which is available to authorized users. Correspondence to: Charles McEwen; e-mail: [email protected]
achieved using matrix-assisted laser desorption/ionization (MALDI) [5] or electrospray ionization (ESI) [6] MS. However, MALDI requires use of a laser, and at vacuum, uses specialized instrumentation, and at AP, specially designed ion sources. Sample introduction for ionization by ESI can be problematic result
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