Molecular and Structural Characterization of Isomeric Compounds in Atmospheric Organic Aerosol Using Ion Mobility-Mass Spectrometry
Molecular and Structural Characterization of Isomeric Compounds in Atmospheric Organic Aerosol Using Ion Mobility-Mass Spectrometry
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使用离子淌度-质谱法对大气有机气溶胶中异构化合物进行分子和结构表征
DOI：
10.1021/acs.jpca.2c06459
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Laskin, Alexander
中科院分区：
文献类型：
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作者：
West, Christopher P.;Mesa Sanchez, Daniela;Morales, Ana C.;Hsu, Yun-Jung;Ryan, Jackson;Darmody, Andrew;Slipchenko, Lyudmila V.;Laskin, Julia;Laskin, Alexander
通过多相大气化学作用形成的二次有机气溶胶(SOA)构成了空气中颗粒物的一大部分。由于不同排放源和大气老化过程的不同，SOA组分的化学组成和分子结构也不同，这给其鉴定带来了困难。在这项工作中，我们使用漂移管离子迁移率光谱和四极杆飞行时间质谱仪(IM-MS)来快速气相分离和多维表征d-柠檬烯(LsoA)和α-蒎烯(PsoA)这两个由异构体单萜烯臭氧分解产生的生物源SOA中的异构体。用电喷雾电离(ESI)对样品进行了电离，并用IM-MS对样品进行了正负两种电离模式的表征。通过多场和单场测量，得到了单组分氮气碰撞截面(DTCCSN2)。一种新的IM多路复用/高分辨率多路分解方法被用于提高灵敏度、改善峰形和增强迁移率基线分辨率，揭示了被测离子的几种异构体结构。对于LSOA和PSOA样品，我们报告了异构体结构的显著差异。使用密度泛函理论的分子结构计算与CCS值的理论建模相结合，可以深入了解LSOA和PSOA组分之间的结构差异。以[M+Na]+离子形式观察到的单体−组分的平均DTCCSN2值比[M-H]SOA组分的DTCCSN2值高3-6%。同时，两个样品中的二聚异构体和三聚异构体组分表现出相反的趋势，[M-H]−离子的相关值分别比[M+Na]+离子高3-7%。结果表明，Na+配位的低聚离子的结构比相应的去质子化物种的结构更紧密。与Na+的配位发生在羰基上的氧原子上，形成紧凑的构型。同时，去质子化的分子由于其在气相中的拉长结构而具有更高的DTCCSN2值。因此，SOA混合物中异构体的DTCCSN2值强烈依赖于ESI中的电离模式。此外，由于结构更坚硬，PSOA单体和二聚体的DTCCSN2值(1-4%)比它们的LSOA对应物大。与非环状柔性LSOA结构相比，PSOA化合物中存在环丁烷环，其官能团指向相反的方向，在气相中形成更紧密的离子。最后，我们研究了直接光解对选定的PSOA组分的化学转化的影响。我们使用IM-MS来揭示与气溶胶光解老化相关的结构变化。这项研究说明了用于检测和注释复杂的SOA混合物中的结构异构体的详细的分子和结构描述符。
Secondary organic aerosol (SOA) formed through multiphase atmospheric chemistry makes up a large fraction of airborne particles. The chemical composition and molecular structures of SOA constituents vary between different emission sources and aging processes in the atmosphere, which complicates their identification. In this work, we employ drift tube ion mobility spectrometry with quadrupole time-of-flight mass spectrometry (IM-MS) detection for rapid gas-phase separation and multidimensional characterization of isomers in two biogenic SOAs produced from ozonolysis of isomeric monoterpenes,d-limonene (LSOA) and α-pinene (PSOA). SOA samples were ionized using electrospray ionization (ESI) and characterized using IM-MS in both positive and negative ionization modes. The IM-derived collision cross sections in nitrogen gas (DTCCSN2) for individual SOA components were obtained using multifield and single-field measurements. A novel application of IM multiplexing/high-resolution demultiplexing methodology was employed to increase sensitivity, improve peak shapes, and augment mobility baseline resolution, which revealed several isomeric structures for the measured ions. For LSOA and PSOA samples, we report significant structural differences of the isomer structures. Molecular structural calculations using density functional theory combined with the theoretical modeling of CCS values provide insights into the structural differences between LSOA and PSOA constituents. The averageDTCCSN2values for monomeric SOA components observed as [M + Na]+ions are 3–6% higher than those of their [M – H]−counterparts. Meanwhile, dimeric and trimeric isomer components in both samples showed an inverse trend with the relevant values of [M – H]−ions being 3–7% higher than their [M + Na]+counterparts, respectively. The results indicate that the structures of Na+-coordinated oligomeric ions are more compact than those of the corresponding deprotonated species. The coordination with Na+occurs on the oxygen atoms of the carbonyl groups leading to a compact configuration. Meanwhile, deprotonated molecules have higherDTCCSN2values due to their elongated structures in the gas phase. Therefore,DTCCSN2values of isomers in SOA mixtures depend strongly on the mode of ionization in ESI. Additionally, PSOA monomers and dimers exhibit largerDTCCSN2values (1–4%) than their LSOA counterparts owing to more rigid structures. A cyclobutane ring is present with functional groups pointing in opposite directions in PSOA compounds, as compared to noncyclic flexible LSOA structures, forming more compact ions in the gas phase. Lastly, we investigated the effects of direct photolysis on the chemical transformations of selected individual PSOA components. We use IM-MS to reveal structural changes associated with aerosol aging by photolysis. This study illustrates the detailed molecular and structural descriptors for the detection and annotation of structural isomers in complex SOA mixtures.