Atmospheric Pressure Laser-Induced Acoustic Desorption Chemical Ionization Mass Spectrometry for Analysis of Saturated Hydrocarbons

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• 作者：Leonard Nyadong ; John P. Quinn ; Chang S. Hsu ; Christopher L. Hendrickson ; Ryan P. Rodgers ; Alan G. Marshall
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：August 21, 2012
• 年：2012
• 卷：84
• 期：16
• 页码：7131-7137
• 全文大小：385K
• 年卷期：v.84,no.16(August 21, 2012)
• ISSN：1520-6882

文摘

We present atmospheric pressure laser-induced acoustic desorption chemical ionization (AP/LIAD-CI) with O₂ carrier/reagent gas as a powerful new approach for the analysis of saturated hydrocarbon mixtures. Nonthermal sample vaporization with subsequent chemical ionization generates abundant ion signals for straight-chain, branched, and cycloalkanes with minimal or no fragmentation. [M 鈥?H]⁺ is the dominant species for straight-chain and branched alkanes. For cycloalkanes, M^{+鈥?/sup> species dominate the mass spectrum at lower capillary temperature (<100 掳C) and [M 鈥?H]+ at higher temperature (>200 掳C). The mass spectrum for a straight-chain alkane mixture (C₂₁鈥揅₄₀) shows comparable ionization efficiency for all components. AP/LIAD-CI produces molecular weight distributions similar to those for gel permeation chromatography for polyethylene polymers, Polywax 500 and Polywax 655. Coupling of the technique to Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for the analysis of complex hydrocarbon mixtures provides unparalleled mass resolution and accuracy to facilitate unambiguous elemental composition assignments, e.g., 1754 peaks (rms error = 175 ppb) corresponding to a paraffin series (C₁₂鈥揅₄₉, double-bond equivalents, DBE = 0) and higher DBE series corresponding to cycloparaffins containing one to eight rings. Isoabundance-contoured plots of DBE versus carbon number highlight steranes (DBE = 4) of carbon number C₂₇鈥揅₃₀ and hopanes of C₂₉鈥揅₃₅ (DBE = 5), with sterane-to-hopane ratio in good agreement with field ionization (FI) mass spectrometry analysis, but performed at atmospheric pressure. The overall speciation of nonpolar, aliphatic hydrocarbon base oil species offers a promising diagnostic probe to characterize crude oil and its products.}