Institute of Organic Chemistry, Heidelberg University, Heidelberg, Germany.
Eur J Mass Spectrom (Chichester). 2023 Feb;29(1):21-32. doi: 10.1177/14690667221133388. Epub 2022 Oct 18.
Field desorption (FD) traditionally is an ionization technique in mass spectrometry (MS) that is performed in high vacuum. So far only two studies have explored FD at atmospheric pressure or even superatmospheric pressure, respectively. This work pursues ion desorption from 13-µm activated tungsten emitters at atmospheric pressure. The emitters are positioned 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 is set to 3-5 kV with respect to the emitter. Under these conditions positive, and for the first time, negative ion desorption is achieved. In either polarity, atmospheric pressure field desorption (APFD) is robust and spectra are reproducible. Both singly charged positive and negative ions formed by these processes are characterized by accurate mass-based formula assignments and in part by tandem mass spectrometry. The compounds analyzed include the ionic liquids trihexyl(tetradecyl) phosphonium tris(pentafluoroethyl) trifluorophosphate) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, the acidic compounds perfluorononanoic acid and polyethylene glycol diacid, as well as two amino-terminated polypropylene glycols. Some surface mobility on the emitter is prerequisite for ion desorption to occur. While ionic liquids inherently provide this mobility, the desorption of ions from solid analytes requires the assistance of a liquid matrix, e.g. glycerol.
场解吸（FD）传统上是质谱（MS）中的一种电离技术，在高真空下进行。到目前为止，只有两项研究分别探索了大气压甚至超大气压下的 FD。本工作旨在探索在大气压下从 13μm 活性钨发射器中进行离子解吸。发射器位于傅里叶变换离子回旋共振（FT-ICR）质谱仪的大气压接口的前面，接口的入口电极相对于发射器设置为 3-5kV。在这些条件下，首次实现了正离子和负离子的解吸。在任一极性下，大气压场解吸（APFD）都是稳定的，且谱图具有可重现性。通过这些过程形成的单电荷正离子和负离子均通过精确质量的公式分配进行了特征化，部分通过串联质谱进行了特征化。分析的化合物包括离子液体三己基（十四烷基）膦三（五氟乙基）三氟磷酸盐）和 1-丁基-1-甲基吡咯烷𬭩双（三氟甲基磺酰基）亚胺、酸性化合物全氟壬酸和聚乙二醇二酸，以及两种氨端聚丙二醇。发射器上的一些表面迁移是离子解吸发生的前提。虽然离子液体固有地提供了这种迁移性，但固体分析物中离子的解吸需要液体基质（例如甘油）的辅助。
