Institute for Instrumental Analytics and Bioanalytics, Mannheim University of Applied Sciences, Paul-Wittsack-Strasse 10, 68163, Mannheim, Germany.
Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146, Hamburg, Germany.
Anal Bioanal Chem. 2021 May;413(13):3551-3560. doi: 10.1007/s00216-021-03306-7. Epub 2021 Apr 10.
The ion mobility spectra of the isomeric monoterpenes α-pinene, β-pinene, myrcene, and limonene in drift tube ion mobility spectrometry (IMS) with H radioactive ionization are highly similar and difficult to distinguish. The aim of this work was to enhance the selectivity of IMS by the addition of nitrogen monoxide (NO) as dopant and to investigate the underlying changes in ion formation responsible for the modified ion signals observed in the ion mobility spectra. Even though H-based-IMS systems have been used in hyphenation with gas chromatography (GC) for profiling of volatile organic compounds (VOCs), the investigation of ion formation still remains challenging and was exemplified by the investigated monoterpenes. Nonetheless, the formation of monomeric, dimeric, and trimeric ion clusters could be tentatively confirmed by a mass-to-mobility correlation and the highly similar pattern of ion signals in the monomer region was attributed to isomerization mechanisms potentially occurring after proton transfer reactions. The addition of NO as dopant could finally lead to the formation of additional product ions and increased the selectivity of IMS for the investigated monoterpenes as confirmed by principal component analysis (PCA). The discrimination of monoterpenes in the volatile profile is highly relevant in the quality control of hops and was given as the example for application. The results indicate that additional product ions were obtained by the formation of NO adduct ions, next to hydride abstraction, charge transfer, or fragmentation reactions. This approach can potentially leverage selectivity issues in VOC profiling of complex matrices, such as food matrices or raw materials in combination with chemometric pattern recognition techniques.
具有放射性氢电离的漂移管离子迁移谱（IMS）中，异构单萜 α-蒎烯、β-蒎烯、月桂烯和柠檬烯的离子迁移谱非常相似，难以区分。本工作的目的是通过添加一氧化氮（NO）作为掺杂剂来提高 IMS 的选择性，并研究导致观察到的离子迁移谱中离子信号改变的离子形成的基本变化。尽管基于 H 的 IMS 系统已用于与气相色谱（GC）的联用，以对挥发性有机化合物（VOC）进行分析，但离子形成的研究仍然具有挑战性，所研究的单萜就是一个例子。尽管如此，通过质荷比与迁移率的相关性，可以初步确认单体、二聚体和三聚体离子簇的形成，并且在单体区域中高度相似的离子信号模式归因于质子转移反应后可能发生的异构化机制。作为掺杂剂添加的 NO 最终可以导致形成额外的产物离子，并通过主成分分析（PCA）确认提高 IMS 对所研究的单萜的选择性。在啤酒花质量控制中，挥发性成分中单萜的区分非常重要，因此作为应用示例给出。结果表明，除了氢化物提取、电荷转移或碎裂反应之外，通过形成 NO 加合物离子还获得了额外的产物离子。这种方法可以与化学计量模式识别技术相结合，在复杂基质（如食品基质或原材料）的 VOC 分析中潜在地解决选择性问题。
