Cody Robert B, Dane A John
JEOL USA, Inc., 11 Dearborn Rd, Peabody, MA, 01960, USA.
Rapid Commun Mass Spectrom. 2016 May 30;30(10):1181-1189. doi: 10.1002/rcm.7552.
Dopants used with Atmospheric Pressure Photoionization (APPI) were examined with the Direct Analysis in Real Time (DART ) ion source operated with argon gas. Charge-exchange and proton transfer reactions were observed by adding toluene, anisole, chlorobenzene and acetone to the DART gas stream, complementing the information obtained by helium DART.
Mass spectra were acquired with a time-of-flight mass spectrometer equipped with a DART ion source operated with argon gas. A syringe pump was used to introduce dopants directly into the DART gas stream through deactivated fused-silica capillary tubing. Samples including polycyclic aromatic hydrocarbons (PAHs), diesel fuel, trinitrotoluene and cannabinoids were deposited onto the sealed end of melting tube, allowed to dry, and the tube was then suspended in the dopant-enhanced DART gas stream.
PAHs could be detected as molecular ions at concentrations in the low parts-per-billion range by using a solution of 0.5% anisole in toluene as a dopant. Argon DART analysis of a diesel fuel sample with the same dopant mixture showed a simpler mass spectrum than obtained by using helium DART. The argon DART mass spectrum was dominated by molecular ions for aromatic compounds, whereas the helium DART mass spectrum showed both molecular ions and protonated molecules. In contrast O attachment DART showed saturated hydrocarbons and oxygen-containing species. Mass spectra for trinitrotoluene with argon DART in negative-ion mode showed a prominent [M - H] peak, whereas conventional helium DART showed both M and [M - H] . Lastly, in analogy to a report in the literature using APPI, positive ions produced by argon DART ionization for delta-9-tetrahydrocannabinol (THC) and cannabidiol showed distinctive product-ion mass spectra.
Dopant-assisted argon DART operates by a mechanism that is analogous to those proposed for dopant-assisted atmospheric-pressure photoionization. Copyright © 2016 John Wiley & Sons, Ltd.
在以氩气运行的实时直接分析（DART）离子源中，对用于大气压光电离（APPI）的掺杂剂进行了研究。通过向DART气流中添加甲苯、苯甲醚、氯苯和丙酮，观察到了电荷交换和质子转移反应，补充了通过氦气DART获得的信息。
使用配备有以氩气运行的DART离子源的飞行时间质谱仪采集质谱。使用注射泵通过去活化的熔融石英毛细管将掺杂剂直接引入DART气流中。将包括多环芳烃（PAH）、柴油、三硝基甲苯和大麻素的样品沉积到熔融管的密封端，使其干燥，然后将该管悬浮在掺杂剂增强的DART气流中。
通过使用0.5%苯甲醚的甲苯溶液作为掺杂剂，可在十亿分率低浓度范围内将PAH检测为分子离子。用相同的掺杂剂混合物对柴油样品进行氩气DART分析，其质谱比使用氦气DART得到的质谱更简单。氩气DART质谱以芳香族化合物的分子离子为主，而氦气DART质谱则同时显示分子离子和质子化分子。相比之下，O附着DART显示出饱和烃和含氧物种。在负离子模式下，用氩气DART对三硝基甲苯进行质谱分析时，显示出一个突出的[M - H]峰，而传统的氦气DART则同时显示出M和[M - H]。最后，类似于文献中使用APPI的报告，氩气DART电离产生的δ-9-四氢大麻酚（THC）和大麻二酚的正离子显示出独特的产物离子质谱。
掺杂剂辅助的氩气DART的运行机制与掺杂剂辅助的大气压光电离所提出的机制类似。版权所有© 2016约翰威立父子有限公司。
