Mechanistic study on lowering the sensitivity of positive atmospheric pressure photoionization mass spectrometric analyses: size-dependent reactivity of solvent clusters
Mechanistic study on lowering the sensitivity of positive atmospheric pressure photoionization mass spectrometric analyses: size-dependent reactivity of solvent clusters
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DOI：
10.1002/rcm.7373
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发表时间：
2015-11-15
影响因子：
2
通讯作者：
Kim, Sunghwan
中科院分区：
文献类型：
--
作者：
Ahmed, Arif;Choi, Cheol Ho;Kim, Sunghwan
基本原理了解大气压光电离 (APPI) 的机制对于采用 APPI 液相色谱/质谱 (LC/MS) 的研究非常重要。在这项研究中，利用质谱分析和量子力学模拟研究了多芳烃（PAH）化合物溶解在甲苯和甲醇或水混合物中的APPI机理。特别是，基于MS数据和量子力学计算的结合，考虑了可能有助于信号减少的四种不同机制。方法通过结合MS数据和密度泛函理论（DFT）计算阐明了APPI机制。为了获得 MS 数据，使用正模式 (+) APPI Q Exactive Orbitrap 质谱仪分析每种溶液。使用通用原子分子电子结构系统（GAMESS）进行DFT计算。结果实验结果表明，甲醇显着降低了（+）APPI中的信号，但当使用水与甲苯作为共溶剂时，没有观察到显着的信号降低。与质子化离子相比，信号降低更为显着，尤其是对于分子离子。因此，由于甲醇对 APPI 效率的负面影响，可以获得有关 (+) APPI-MS 中甲醇诱导的信号减少机制的重要信息。结论甲醇簇 ((CH3OH)(n)，n=1-8) 的尺寸依赖性反应性是决定 (+) APPI-MS 分析灵敏度的重要因素。簇可以与甲苯自由基离子竞争电子。随着甲醇簇尺寸的增加，反应性增加，这种效应可能是由溶剂簇的尺寸依赖性电离能引起的。由此产生的簇反应性增加解释了在分析物中观察到的流速和温度依赖性信号减少。根据此处提供的结果，最小化甲醇簇的尺寸可以提高 LC/(+)-APPI-MS 的灵敏度。版权所有 (c) 2015 约翰·威利父子有限公司
RationaleUnderstanding the mechanism of atmospheric pressure photoionization (APPI) is important for studies employing APPI liquid chromatography/mass spectrometry (LC/MS). In this study, the APPI mechanism for polyaromatic hydrocarbon (PAH) compounds dissolved in toluene and methanol or water mixture was investigated by use of MS analysis and quantum mechanical simulation. In particular, four different mechanisms that could contribute to the signal reduction were considered based on a combination of MS data and quantum mechanical calculations.MethodsThe APPI mechanism is clarified by combining MS data and density functional theory (DFT) calculations. To obtain MS data, a positive-mode (+) APPI Q Exactive Orbitrap mass spectrometer was used to analyze each solution. DFT calculations were performed using the general atomic and molecular electronic structure system (GAMESS).ResultsThe experimental results indicated that methanol significantly reduced the signal in (+) APPI, but no significative signal reduction was observed when water was used as a co-solvent with toluene. The signal reduction is more significant especially for molecular ions than for protonated ions. Therefore, important information about the mechanism of methanol-induced signal reduction in (+) APPI-MS can be gained due its negative impact on APPI efficiency.ConclusionsThe size-dependent reactivity of methanol clusters ((CH3OH)(n), n=1-8) is an important factor in determining the sensitivity of (+) APPI-MS analyses. Clusters can compete with toluene radical ions for electrons. The reactivity increases as the sizes of the methanol clusters increase and this effect can be caused by the size-dependent ionization energy of the solvent clusters. The resulting increase in cluster reactivity explains the flow rate and temperature-dependent signal reduction observed in the analytes. Based on the results presented here, minimizing the sizes of methanol clusters can improve the sensitivity of LC/(+)-APPI-MS. Copyright (c) 2015 John Wiley & Sons, Ltd.