Detection of weakly bound clusters in incipiently sooting flames via ion seeded dilution and collision charging for (APi-TOF) mass spectrometry analysis
Detection of weakly bound clusters in incipiently sooting flames via ion seeded dilution and collision charging for (APi-TOF) mass spectrometry analysis
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DOI：
10.1016/j.fuel.2020.119820
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发表时间：
2021-04
期刊：
影响因子：
7.4
通讯作者：
F. Carbone;M. Canagaratna;A. Lambe;J. Jayne;D. Worsnop;A. Gomez
中科院分区：
文献类型：
--
作者：
F. Carbone;M. Canagaratna;A. Lambe;J. Jayne;D. Worsnop;A. Gomez
本研究引入了一种大气压化学电离方法，该方法依赖于气雾化分析物与样品稀释流中预先接种的双极离子的低能热碰撞（即 <0.05 eV），并允许检测弱结合的分子簇。在此，通过对乙烯和空气的层流预混合火焰进行质谱分析，在烟灰起始的背景下探索了该方法的潜力，通过微小孔口对产物进行采样，并在预流经基于 Kr85 的中和器的氮气中快速稀释以产生双极性离子。使用大气压接口飞行时间（APi-TOF，Tofwerk AG）质谱仪进行分析，该质谱仪具有高灵敏度、质量准确度和分辨率（超过 4000），可以将火焰产物与预先接种的离子区分开来。由于中性物质的电离是通过离子附着或离子碰撞后的电荷交换发生的，因此识别测量的质谱中每个峰的起源并非易事。尽管如此，结果提供了有关在任一极性下电离的中性火焰产物的总体元素组成的有价值的信息。结果表明，轻于 400 Da 且 C/H 比在 2 到 3 之间的碳氢化合物的聚集会导致火焰中产生烟灰。火焰产物的脱氢预计会在火焰中对流时发生，但仅在正极性测量中观察到，因为烟灰核和前体获得正电荷而不是负电荷的可能性更高。
This study introduces an atmospheric pressure chemical ionization method that relies on low-energy thermal collisions (i.e., <0.05 eV) of aerosolized analytes with bipolar ions pre-seeded in a sample dilution flow and allows for the detection of weakly bound molecular clusters. Herein, the potential of the method is explored in the context of soot inception by performing mass spectrometric analysis of a laminar premixed flame of ethylene and air whose products are sampled through a tiny orifice and quickly diluted in nitrogen pre-flowed through a Kr85based neutralizer to generate the bipolar ions. Analyses were performed with an Atmospheric Pressure Interface Time-of-Flight (APi-TOF, Tofwerk AG) Mass Spectrometer whose high sensitivity, mass accuracy, and resolution (over 4000) allowed for the discrimination of the flame products from the pre-seeded ions. Since ionization of neutrals occurs by either ion attachment or charge exchange following ion collision, the identification of the origin of each peak in the measured mass spectra is not-trivial. Nevertheless, the results provide valuable information on the overall elemental composition of the neutral flame products ionized in either polarity. Results show that the clustering of hydrocarbons lighter than 400 Da and having a C/H ratio between 2 and 3 leads to soot inception in the flame. The dehydrogenation of the flame products, expected to occur as they are convected in the flame, is observed only for measurements in positive polarity because of a higher probability of soot nuclei and precursors to get a positive rather than a negative charge.