Mechanisms Behind the Generation of Protonated Ions for Polyaromatic Hydrocarbons by Atmospheric Pressure Photoionization

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• 作者：Arif Ahmed ; Cheol Ho Choi ; Myoung Choul Choi ; Sunghwan Kim
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：January 17, 2012
• 年：2012
• 卷：84
• 期：2
• 页码：1146-1151
• 全文大小：314K
• 年卷期：v.84,no.2(January 17, 2012)
• ISSN：1520-6882

文摘

In this study, the mechanism behind the generation of protonated polyaromatic hydrocarbon (PAH) ions without heteroatoms by atmospheric pressure photoionization (APPI) is investigated. Comparing data obtained by APPI of anthracene dissolved either in toluene or perdeuterated toluene suggests that toluene acts as a source of protons and that breakage of C鈥揌 bonds in the toluene molecule is important for the overall protonation reaction. Our data describing an Arrhenius-type temperature-dependent relationship between the signal intensities of molecular and protonated ions suggest a mechanistic relation between the generated molecular and protonated ions. The APPI protonation mechanism that best explains the observed phenomena is composed of two reactions: electron transfer followed by hydrogen transfer. This two-step mechanism for APPI was originally suggested by Syage (Syage, J. A. J. Am. Soc. Mass Spectrom. 2004, 15, 1521鈭?533). Further quantum mechanical study shows that an energetically favorable ion鈥搈olecular complex can be generated as a result of electron transfer from toluene to PAH, which subsequently facilitates hydrogen transfer. This suggests that both electron transfer and hydrogen transfer can occur as a 鈥渃oncerted鈥?reaction through the ion鈥搈olecular complex precursor state, which is consistent with experimental results. To our best knowledge, this is the first time that the dynamic nature of the APPI process is clearly revealed by combined experimental and quantum mechanical studies.