Weber Markus, Wolf Jan-Christoph, Haisch Christoph
Chair of Analytical Chemistry and Water Chemistry, Technical University of Munich, 85748 Garching, Germany.
Plasmion GmbH, 86167 Augsburg, Germany.
J Am Soc Mass Spectrom. 2023 Apr 5;34(4):538-549. doi: 10.1021/jasms.2c00279. Epub 2023 Feb 24.
Cold plasma-based ionization techniques allow for soft ionization of a wide variety of chemical compounds. In this chemical ionization mechanism, the atmosphere plays a crucial role in ionization. Knowing its influence is critical for the optimization of analysis conditions and interpretation of resulting spectra. This study uses soft ionization by chemical reaction in transfer (SICRIT), a variant of dielectric barrier discharge ionization (DBDI), that allows for a controlled atmosphere to investigate atmosphere and dopant effects. The influence of eight makeup gas compositions (dry nitrogen, room air, and nitrogen-enriched with either water, HCl, MeOH, hexane, NH, and fluorobenzene) on the ionization with SICRIT was investigated. Fifteen compound classes, comprising alkanes, polyaromatic hydrocarbons (PAHs), terpenes, oxygen-containing terpenes, alkylphenols, chlorophenols, nitrophenols, trialkylamines, triazines, phthalates with or without ether groups, aldehydes, ketones, fatty acid methyl esters (FAMEs), and polyoxy-methylene ethers (OMEs) were measured via gas chromatography SICRIT high-resolution mass spectrometry (GC-SICRIT-HRMS). The different atmospheres were compared in terms of generated ions, ion intensities and fragmentation during ionization. Measurements of reactant ions were performed for a better understanding of the underlying mechanisms. All 15 compound classes were mostly softly ionized. For most compound classes and atmospheres, protonation is the dominant ionization mode. The highest number of compounds ionized via protonation was observed in dry nitrogen, followed by room air and humid nitrogen. The study should work as a guideline for the choice of atmosphere for specific compound classes and the interpretation of spectra generated under a specific atmosphere.
基于冷等离子体的电离技术可实现多种化合物的软电离。在这种化学电离机制中，气氛在电离过程中起着至关重要的作用。了解其影响对于优化分析条件和解释所得光谱至关重要。本研究采用转移化学反应软电离（SICRIT），这是一种介质阻挡放电电离（DBDI）的变体，它允许在可控气氛下研究气氛和掺杂剂的影响。研究了八种补充气体组成（干燥氮气、室内空气以及富含水、HCl、甲醇、己烷、NH和氟苯的氮气）对SICRIT电离的影响。通过气相色谱SICRIT高分辨率质谱（GC-SICRIT-HRMS）测量了十五类化合物，包括烷烃、多环芳烃（PAH）、萜烯、含氧萜烯、烷基酚、氯酚、硝基酚、三烷基胺、三嗪、含或不含醚基的邻苯二甲酸酯、醛、酮、脂肪酸甲酯（FAME）和聚氧化甲烯醚（OME）。比较了不同气氛下电离过程中产生的离子、离子强度和碎片情况。进行了反应物离子的测量以更好地理解其潜在机制。所有十五类化合物大多被软电离。对于大多数化合物类别和气氛，质子化是主要的电离模式。在干燥氮气中观察到通过质子化电离的化合物数量最多，其次是室内空气和潮湿氮气。该研究可为特定化合物类别的气氛选择以及特定气氛下产生的光谱解释提供指导。
