University of Natural Resources and Life Sciences, Vienna, Department of Chemistry, Institute of Analytical Chemistry, Muthgasse 18, 1190 Vienna, Austria.
J Am Soc Mass Spectrom. 2022 Jun 1;33(6):961-973. doi: 10.1021/jasms.2c00034. Epub 2022 May 12.
Ionization of organic compounds with different structural and energetic properties including benzene derivatives, polycyclic aromatic hydrocarbons (PAHs), ketones, and polyenes was studied using a commercial atmospheric pressure corona discharge (APCI) ion source on a drift tube ion mobility-quadrupole-time-of-flight mass spectrometer (IM-QTOFMS). It was found that the studied cohort of compounds can be experimentally ionized via protonation, charge transfer, and hydride abstraction leading to formation of [M + H], [M], and [M - H] species, respectively. By experimentally monitoring the product ions and comparing the thermodynamic data for different ionization paths, it was proposed that NO is one of the main reactant ions (RIs) in the ion source used. Of particular focus in this work were theoretical and experimental studies of the effect of solvents frequently used for analytical applications with this ion source (acetonitrile, methanol, and chloroform) on the ionization mechanisms. In methanol, the studied compounds were observed to be ionized mainly via proton transfer while acetonitrile suppressed the protonation of compounds and enhanced their ionization via charge transfer and hydride abstraction. Use of chloroform as a solvent led to formation of CHCl as an alternative reactant ion (RI) to ionize the analytes via electrophilic substitution. Density functional theory (DFT) was used to study the different paths of ionization. The theoretical and experimental results showed that by using only the absolute thermodynamic data, the real ionization path cannot be determined and the energies of all competing processes such as charge transfer, protonation, and hydride abstraction need to be compared.
采用商业大气压电晕放电（APCI）离子源在漂移管离子淌度-四极杆-飞行时间质谱仪（IM-QTOFMS）上研究了具有不同结构和能量特性的有机化合物的电离，包括苯衍生物、多环芳烃（PAHs）、酮和多烯。研究发现，所研究的化合物可以通过质子化、电荷转移和氢化物提取实验性地进行电离，分别形成[M+H]、[M]和[M-H]物种。通过实验监测产物离子并比较不同电离途径的热力学数据，提出 NO 是所用离子源中的主要反应离子（RIs）之一。在这项工作中，特别关注的是理论和实验研究用于分析应用的溶剂（乙腈、甲醇和氯仿）对该离子源的电离机制的影响。在甲醇中，研究的化合物主要通过质子转移进行电离，而乙腈抑制了化合物的质子化，并通过电荷转移和氢化物提取增强了它们的电离。使用氯仿作为溶剂导致 CHCl 形成作为替代反应离子（RI），通过亲电取代作用电离分析物。密度泛函理论（DFT）用于研究不同的电离途径。理论和实验结果表明，仅使用绝对热力学数据无法确定实际的电离途径，需要比较所有竞争过程（如电荷转移、质子化和氢化物提取）的能量。
