Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
MS-Cheminformatics LLC, 2-13-21 Sasaonishi, Toin, Mie 511-0231, Japan.
Anal Chem. 2021 May 4;93(17):6589-6593. doi: 10.1021/acs.analchem.1c00898. Epub 2021 Apr 23.
Proton-transfer-reaction (PTR) mass spectrometry (MS) is capable of detecting trace-level volatile organic compounds (VOCs) in gaseous samples in real time. Therefore, PTR-MS has become a popular method in many different study areas. Most of the currently reported PTR-MS applications are designed to determine volatile compounds. However, the method might be applicable for nonvolatile organic compound detection. Supercritical fluid chromatography (SFC) has been studied in the last 5 decades. This approach has high separation efficiency and predictable retention behavior, making separation optimization easy. Atmospheric ionization techniques, such as atmospheric chemical ionization (APCI) and electrospray ionization (ESI), are the most studied SFC-MS interfaces. These processes require the addition of makeup solvents to prevent precipitation or crystallization of the solute while depressurizing the mobile phase. In contrast, the PTR process is carried out in a vacuum; supercritical carbon dioxide may release solute into the PTR flow tube without a phase transition as long as it is maintained above a critical temperature. Therefore, this might constitute yet another use for the SFC-MS interface. Caffeine and a few other nonpolar compounds in supercritical carbon dioxide were successfully detected with time-of-flight MS without adding solvent by using preliminarily assembled supercritical flow injection and supercritical fluid extraction (SFE)-PTR interfaces.
质子转移反应（PTR）质谱（MS）能够实时检测气态样品中的痕量挥发性有机化合物（VOC）。因此，PTR-MS 已成为许多不同研究领域中流行的方法。目前报道的大多数 PTR-MS 应用程序旨在确定挥发性化合物。然而，该方法可能适用于非挥发性有机化合物的检测。超临界流体色谱（SFC）在过去的 50 年中得到了研究。这种方法具有高分离效率和可预测的保留行为，使分离优化变得容易。大气电离技术，如大气压化学电离（APCI）和电喷雾电离（ESI），是研究最多的 SFC-MS 接口。这些过程需要添加组成溶剂以防止在降低流动相压力时溶质沉淀或结晶。相比之下，PTR 过程在真空中进行；只要超临界二氧化碳保持在临界温度以上，它就可能在不发生相变的情况下将溶质释放到 PTR 流管中。因此，这可能构成 SFC-MS 接口的另一种用途。通过使用初步组装的超临界流动注射和超临界流体萃取（SFE）-PTR 接口，在不添加溶剂的情况下，成功地使用飞行时间 MS 检测了超临界二氧化碳中的咖啡因和其他一些非极性化合物。
