Effects of aerosol size and coating thickness on the molecular detection using extractive electrospray ionization
Effects of aerosol size and coating thickness on the molecular detection using extractive electrospray ionization
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DOI：
10.5194/amt-14-5913-2021
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发表时间：
2021-09-02
影响因子：
3.8
通讯作者：
El Haddad, Imad
中科院分区：
文献类型：
--
作者：
Lee, Chuan Ping;Surdu, Mihnea;El Haddad, Imad
二十多年来，萃取电喷雾电离 (EESI) 一直是一种众所周知的技术，可用于化学反应产物和中间体的高通量在线分子表征、天然生物分子检测、体内代谢组学以及环境监测，且热和电离引起的碎片可忽略不计。然而，EESI 提取机制仍不确定。先前的研究对于直径在 20 至 400 nm 之间的颗粒是否被完全提取或者提取是否仅限于表面层存在分歧。在这里，我们通过评估粒径和涂层厚度对其中分子检测的影响来检查分析物提取机制。我们发现颗粒被完全提取：具有固定核心体积（直径为 156 和 226 nm，无涂层）的有机物涂层 NH4NO3 颗粒显示出恒定的 NH4NO3 EESI 信号，与壳涂层厚度无关，而构成壳的次级有机分子的信号与壳体积成比例变化。我们还发现，EESI 灵敏度表现出强烈的尺寸依赖性，随着粒径从 300 nm 减小到 30 nm，灵敏度增加 1-3 个数量级。这种依赖性随电喷雾 (ES) 液滴尺寸、颗粒尺寸和 EESI 入口中凝结的停留时间而变化，表明 EESI 灵敏度受到颗粒和 ES 液滴之间的凝结系数的影响。总的来说，我们的结果表明，在 EESI 中，当颗粒被 ES 液滴收集时，无论其化学成分如何，它们都会被 ES 液滴完全提取。然而，它们的合并并不完全，并且很大程度上取决于它们的大小。当 EESI 用于探测尺寸变化的颗粒时，这种尺寸依赖性尤其重要，例如尺寸范围低于 100 nm 的气溶胶形成和生长研究的情况。
Extractive electrospray ionization (EESI) has been a well-known technique for high-throughput online molecular characterization of chemical reaction products and intermediates, detection of native biomolecules, in vivo metabolomics, and environmental monitoring with negligible thermal and ionization-induced fragmentation for over two decades. However, the EESI extraction mechanism remains uncertain. Prior studies disagree on whether particles between 20 and 400 nm diameter are fully extracted or if the extraction is limited to the surface layer. Here, we examined the analyte extraction mechanism by assessing the influence of particle size and coating thickness on the detection of the molecules therein. We find that particles are extracted fully: organics-coated NH4NO3 particles with a fixed core volume (156 and 226 nm in diameter without coating) showed constant EESI signals for NH4NO3 independent of the shell coating thickness, while the signals of the secondary organic molecules comprising the shell varied proportionally to the shell volume. We also found that the EESI sensitivity exhibited a strong size dependence, with an increase in sensitivity by 1-3 orders of magnitude as particle size decreased from 300 to 30 nm. This dependence varied with the electrospray (ES) droplet size, the particle size and the residence time for coagulation in the EESI inlet, suggesting that the EESI sensitivity was influenced by the coagulation coefficient between particles and ES droplets. Overall, our results indicate that, in the EESI, particles are fully extracted by the ES droplets regardless of the chemical composition, when they are collected by the ES droplets. However, their coalescence is not complete and depends strongly on their size. This size dependence is especially relevant when EESI is used to probe size-varying particles as is the case in aerosol formation and growth studies with size ranges below 100 nm.