Recent Development on the Detection and Monitoring of Chemical Intermediates by Ambient Mass Spectrometry

Along with the development of science and technology, chemical reactions exhibit an important role in various fileds including synthesis, chemical engineering, energy, environment, biology and medicine. The effective intermediates monitoring and mechanism exploration of chemical reactions can promote their development and contribute to the design of new chemical reactions. However, in the complex reaction matrix, a variety of intermediates with different molecular weights, life and dynamic changes will be generated at different reaction conditions, the effective capture and structure determinations of the short-lived and active reaction intermediates are hard to be achieved. In recent years, ambient mass spectrometry (AMS) has been widely used in the detection of chemical intermediates to explore reaction mechanisms, due to its advantages of high sensitivity, high selectivity, rapid analysis and in-situ monitoring. Herein, the research progress and development of AMS for the detection of reaction intermediates were reviewed, which involved the reactions in the fields of electrochemistry, photochemistry, plasma chemistry and microdroplet chemistry. For different types of reactions, the designs of different AMS detection technologies were introduced in details. Upon the different ionization strategies, different kinds of techniques have been reported, including desorption electrospray ionization mass spectrometry (DESI-MS), nano-electrospray ionization mass spectrometry (nESI-MS), extraction electrospray ionization mass spectrometry (EESI-MS), Venturi easy ambient sonic spray ionization mass spectrometry (VEASI-MS), spray-dependent plasma mass spectrometry (SDP-MS), accelerated plasma degradation coupled with electrospray ionization mass spectrometry (APD-MS), field-induced droplet ionization mass spectrometry (FIDI-MS) and so on. Subsequently, the progress and application of these mass spectrometry techniques in capturing intermediates of different kinds of reactions as well as the exploration of mechanisms were reviewed. Finally, the development of mass spectrometry for the detection of transient reaction intermediates in different chemical reactions, including electrochemical reactions, photochemical reactions, plasma reactions and microdroplet reactions were summarized and prospected. As reviewed, based on the characteristics of high throughput virtual screening and online monitoring, as well as the diversification of ion sources, AMS would be widely used in various fields including industrial production, environmental protection, energy and so on. In the future, the improved AMS techniques will be encouraged for examining more highly active intermediates with the increasing requirements for the examination of complicated reactions.