Analytical Chemistry Core Laboratory, King Abdullah University Of Science and Technology, Thuwal, Kingdom of Saudi Arabia.
Rapid Commun Mass Spectrom. 2012 Nov 15;26(21):2517-25. doi: 10.1002/rcm.6373.
An ethanol-based multicomponent dopant consisting of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v/v/v) has been used as a dopant for atmospheric pressure photoionization (APPI) of polycyclic aromatic hydrocarbons (PAHs). In this study the mechanism of ionization of PAHs assisted by the ethanol-based multicomponent dopant is investigated.
The reactant background cluster ions of the ethanol-based multicomponent dopant observed in the positive ion APPI were studied. These studies were performed to investigate the mechanism behind the generation of a molecular radical cation (M(+•)) for PAHs by APPI assisted by the ethanol-based multicomponent dopant. Full scan and MS/MS analyses were conducted using an LTQ Orbitrap mass spectrometer. The effect of acidification of the mobile phase on the dopant cluster ion formation was also investigated.
With the ethanol-based multicomponent dopant, a single type of molecular radical cation M(+•) was observed for the studied PAHs. The characteristic ion signal of the multicomponent dopant mixture consisted of mainly anisole photoions at m/z 108.05697 and its adduct ions at m/z 124.05188 and 164.07061. The anisole ion response at m/z 108.05697 was stable in the presence of acetonitrile, methanol, water and 0.1% formic acid mobile phase composition.
The abundance formation of anisole photoions shows the universality of this multicomponent dopant in ionizing compounds with ionization energy ranging from 7.1-8.2 eV. Since the ionization energy of anisole is 8.2 eV and is lower than those of chlorobenzene (9.07 eV) and bromobenzene (9.0 eV), the mechanism of formation of anisole photoions even with its very minute amounts was not only governed by its photoionization by the krypton lamp photon energy (10.0 eV and 10.6 eV), but also by charge transfer from bromobenzene and chlorobenzene radical cations. PAH molecules were mainly ionized by charge transfer reaction from photoionized anisole and oxidized anisole radical cations as well as by the krypton lamp.
一种由乙醇/氯苯/溴苯/苯甲醚（98.975:0.1:0.9:0.025，v/v/v/v）组成的基于乙醇的多组分掺杂剂已被用作多环芳烃（PAHs）大气压光解（APPI）的掺杂剂。在这项研究中，研究了 PAHs 被基于乙醇的多组分掺杂剂辅助光解时的电离机制。
研究了在正离子 APPI 中观察到的基于乙醇的多组分掺杂剂的反应物背景簇离子。这些研究旨在探讨通过基于乙醇的多组分掺杂剂辅助的 APPI 为 PAHs 生成分子自由基阳离子（M(+•)）的机制。使用 LTQ Orbitrap 质谱仪进行全扫描和 MS/MS 分析。还研究了流动相酸化对掺杂剂簇离子形成的影响。
使用基于乙醇的多组分掺杂剂，仅观察到研究的 PAHs 的单一类型的分子自由基阳离子 M(+•)。多组分掺杂剂混合物的特征离子信号主要由苯甲醚光离子组成，其质荷比为 m/z 108.05697 及其加合物离子 m/z 124.05188 和 164.07061。在含有乙腈、甲醇、水和 0.1%甲酸的流动相组成中，苯甲醚离子 m/z 108.05697 的响应稳定。
苯甲醚光离子的丰度形成表明该多组分掺杂剂在电离能范围为 7.1-8.2eV 的化合物中具有普遍性。由于苯甲醚的电离能为 8.2eV，低于氯苯（9.07eV）和溴苯（9.0eV），因此苯甲醚光离子的形成机制不仅受其受氪灯光子能量（10.0eV 和 10.6eV）的光致电离控制，还受溴苯和氯苯自由基阳离子的电荷转移控制。PAH 分子主要通过光致电离的苯甲醚和氧化的苯甲醚自由基阳离子的电荷转移反应以及氪灯被离子化。
