Determination of Relative Ionization Cross Sections for Resonance Enhanced Multiphoton Ionization of Polycyclic Aromatic Hydrocarbons
Determination of Relative Ionization Cross Sections for Resonance Enhanced Multiphoton Ionization of Polycyclic Aromatic Hydrocarbons
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DOI：
10.3390/app8091617
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发表时间：
2018-09-01
影响因子：
2.7
通讯作者：
Zimmermann, Ralf
中科院分区：
文献类型：
--
作者：
Gehm, Christian;Streibel, Thorsten;Zimmermann, Ralf
共振增强多光子电离(REMPI)是一种高效、灵敏地测定混合气体中多环芳烃(PAHs)的方法。在REMPI中，离子是通过至少两个光子的吸收而产生的，其中包括定义的电子中间态。因此，与其他基于激光的电离技术一样，光谱选择性也参与到电离过程中。然而，这些依赖于波长的电离速率阻碍了使用REMPI的定量。为此，相对光电离截面(RelPICS)提供了一种易于使用的方法来量化REMPI-MS测量。据此，将单一化合物的电离行为与给定浓度的参照物的电离行为进行了比较。本研究用两种不同的飞行时间质谱仪(TOFMS)测定了266 nm和248 nm波长处部分单核芳烃和多环芳烃的相对分子质量。对于多环芳烃，获得了与外加激光强度强烈相关的relPICS。相比之下，对于单核芳烃，测定了relPICS的常数值。对于小芳烃(如苯)，在两个TOFMS系统之间发现了relPICS的偏差，这可以归因于特定系统中UV生成的差异。然而，这项研究的RelPICS被发现与以前的结果很好地一致，并且可以用于系统无关的定量。
Resonance enhanced multiphoton ionization (REMPI) is a powerful method for the sensitive determination of polycyclic aromatic hydrocarbons (PAHs) in gaseous mixtures via mass spectrometry (MS). In REMPI, ions are produced by the absorption of at least two photons including defined electronic intermediate states. As a resultunlike other laser-based ionization techniquesspectroscopic selectivity is involved into the ionization process. Nevertheless, these wavelength-dependent ionization rates impede the quantification using REMPI. For this purpose, relative photoionization cross sections (relPICS) give an easy-to-use approach to quantify REMPI-MS measurements. Hereby, the ionization behavior of a single compound was compared to that of a reference substance of a given concentration. In this study, relPICS of selected single-core aromatics and PAHs at wavelengths of 266 nm and 248 nm were determined using two different time-of-flight mass spectrometric systems (TOFMS). For PAHs, relPICS were obtained which showed a strong dependence on the applied laser intensity. In contrast, for single-core aromatics, constant values of relPICS were determined. Deviations of relPICS between both TOFMS systems were found for small aromatics (e.g., benzene), which can be assigned to the differences in UV generation in the particular system. However, the relPICS of this study were found to be in good agreement with previous results and can be used for system-independent quantification.