Derpmann Valerie, Mueller David, Bejan Iustinian, Sonderfeld Hannah, Wilberscheid Sonja, Koppmann Ralf, Brockmann Klaus J, Benter Thorsten
Department of Physical and Theoretical Chemistry, University of Wuppertal, 42119, Wuppertal, Germany,
J Am Soc Mass Spectrom. 2014 Mar;25(3):329-42. doi: 10.1007/s13361-013-0761-3. Epub 2014 Jan 8.
We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.
我们分别报道了一种用于对具有较高电子亲和力的化合物（如硝基芳香族化合物）或气相酸度的化合物（如酚类）进行大气压电离的新方法。该方法基于通过光电效应产生热电子，随后当以空气为气体基质时，热电子捕获氧生成O2(-)，或以氮气为基质时直接捕获分析物。O2(-)的电荷转移或质子夺取导致分析物电离。紫外光与金属的相互作用是在大气压下产生热电子的一种清洁方法。此外，与放电或掺杂辅助方法相比，该方法仅产生负离子，且中性自由基的形成被最小化。电离发生在质谱仪的传输毛细管内，导致离子传输到质谱仪高真空区域的时间相对较短。这极大地减少了离子转化过程，从而得到与中性分析物分布更密切相关的质谱图。因此，cAPECI是一种软且选择性的电离方法，检测限在pptV范围内。与标准电离方法（如PTR）相比，cAPECI在选择性和可实现的检测限方面均更具优势。cAPECI被证明是一种在相关领域（如爆炸物检测和大气化学）应用中有前景的电离方法。
