Analytical and Bioanalytical Chemistry ( IF 3.8 ) Pub Date : 2023-03-24 , DOI: 10.1007/s00216-023-04652-4 Matthias Hoyer 1 , Jürgen H Gross 1
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Atmospheric pressure field desorption (APFD) mass spectrometry (MS) has recently been explored as a new contribution to the field of ambient desorption/ionization (ADI). Depending on the selected polarity applied to the field emitter, ionic and polar analytes were demonstrated to deliver positive as well as negative ions. Whereas this recent study solely reported on the formation of even-electron ions of either polarity, the present work on APFD-MS demonstrates the abundant formation of positive molecular ions, M+•, from polycyclic aromatic compounds. Molecular ions were formed on and desorbed from standard 13-µm activated tungsten wire emitters at atmospheric pressure. The commercial field emitters were positioned at about 2 mm distance in front of the atmospheric pressure interface of a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer and the entrance electrode of the interface was set to –4.5 to –5.5 kV with respect to the emitter. Emitter-disrupting electric discharges did normally not occur under these conditions. The electric field strengths achieved at the dendritic microneedles were sufficient to allow for the abundant formation of M+• ions of various polycyclic aromatic compounds such as benzo[a]pyrene, anthracene, fluoranthene, 1,1,4,4-tetraphenyl-butadiene, and 1-aza-[6]helicene. In case of the extremely basic 1-aza-[6]helicene protonation strongly competed with molecular ion formation and tended to suppress the field ionization process. All molecular ion compositions were assured by accurate mass-based formula assignments.
Graphical Abstract
中文翻译：
大气压场解吸质谱中激活场发射器的分子离子形成
大气压场解吸 (APFD) 质谱 (MS) 最近被探索为对环境解吸/电离 (ADI) 领域的新贡献。根据应用于场发射器的所选极性，离子和极性分析物被证明可以传递正离子和负离子。虽然这项最近的研究仅报告了任一极性的偶电子离子的形成，但目前在 APFD-MS 上的工作证明了大量正分子离子的形成，M + •, 来自多环芳族化合物。在大气压力下，分子离子在标准 13 µm 活性钨丝发射器上形成并从中解吸。商用场发射器位于傅立叶变换离子回旋共振 (FT-ICR) 质谱仪大气压力界面前方约 2 mm 的距离处，界面的入口电极设置为 –4.5 至 –5.5 kV，使用关于发射器。在这些条件下通常不会发生发射极干扰放电。在树枝状微针处获得的电场强度足以允许大量形成 M +•苯并[a]芘、蒽、荧蒽、1,1,4,4-四苯基丁二烯和1-氮杂-[6]螺烯等各种多环芳族化合物的离子。在极其基本的 1-aza-[6]helicene 质子化与分子离子形成强烈竞争的情况下，往往会抑制场电离过程。所有分子离子组成均通过精确的基于质量的分子式分配来确保。
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