The Ionization Mechanisms in Direct and Dopant-Assisted Atmospheric Pressure Photoionization and Atmospheric Pressure Laser Ionization
The Ionization Mechanisms in Direct and Dopant-Assisted Atmospheric Pressure Photoionization and Atmospheric Pressure Laser Ionization
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DOI：
10.1007/s13361-014-0988-7
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发表时间：
2014-11-01
影响因子：
3.2
通讯作者：
Benter, Thorsten
中科院分区：
文献类型：
--
作者：
Kauppila, Tiina J.;Kersten, Hendrik;Benter, Thorsten
利用一种新型的气密性API接口，研究了直接光电离和掺杂剂辅助大气压光电离（APPI）及大气压激光电离（APLI）的电离机理。八个分析物（苯，溴苯，萘，蒽，苯甲醛，吡啶，喹诺酮，吖啶）与不同的电离能（IE）和质子亲和力（PA），和四个常见的APPI掺杂剂（甲苯，丙酮，苯甲醚，氯苯）被选中。所有研究的化合物被电离的直接APPI，形成主要的分子离子。掺杂剂的添加抑制了具有高于掺杂剂的IE的IE的分析物的信号。对于具有合适IE或Pas的化合物，掺杂剂增加了电离效率，因为分析物可以通过掺杂剂介导的气相反应电离，例如电荷交换、质子转移和其他相当意外的反应，例如在氯苯存在下形成[M+77]（+）。用氘代甲苯作为掺杂剂的实验证实，在质子转移的情况下，质子源自掺杂剂而不是质子结合的溶剂簇，如在常规开放或非紧密APPI源中。在使用266 nm激光的直接APLI中，由于极高的IE或不利的双光子吸收截面，比在直接APPI中更窄范围的化合物被电离。在APLI系统中引入掺杂剂改变了电离机制，使其与APPI中的掺杂剂发生类似的掺杂剂介导的气相反应，该反应主要产生与APPI中相同形式的离子，并且比直接APLI电离更宽范围的分析物。
A novel, gas-tight API interface for gas chromatography-mass spectrometry was used to study the ionization mechanism in direct and dopant-assisted atmospheric pressure photoionization (APPI) and atmospheric pressure laser ionization (APLI). Eight analytes (ethylbenzene, bromobenzene, naphthalene, anthracene, benzaldehyde, pyridine, quinolone, and acridine) with varying ionization energies (IEs) and proton affinities (PAs), and four common APPI dopants (toluene, acetone, anisole, and chlorobenzene) were chosen. All the studied compounds were ionized by direct APPI, forming mainly molecular ions. Addition of dopants suppressed the signal of the analytes with IEs above the IE of the dopant. For compounds with suitable IEs or Pas, the dopants increased the ionization efficiency as the analytes could be ionized through dopant-mediated gas-phase reactions, such as charge exchange, proton transfer, and other rather unexpected reactions, such as formation of [M+77](+) in the presence of chlorobenzene. Experiments with deuterated toluene as the dopant verified that in case of proton transfer, the proton originated from the dopant instead of proton-bound solvent clusters, as in conventional open or non-tight APPI sources. In direct APLI using a 266 nm laser, a narrower range of compounds was ionized than in direct APPI, because of exceedingly high IEs or unfavorable two-photon absorption cross-sections. Introduction of dopants in the APLI systemchanged the ionization mechanism to similar dopant-mediated gas-phase reactions with the dopant as in APPI, which produced mainly ions of the same form as in APPI, and ionized a wider range of analytes than direct APLI.