Intermediate detection in real time using reactive surface desorption dielectric-barrier discharge ionization mass spectrometry.

Reactive intermediates play key roles for reaction mechanism elucidation. A suitable tool for identifying the key intermediates is crucial and highly desirable. In this study, surface desorption dielectric-barrier discharge ionization (reactive SDDBDI) was developed for characterization of the reactive intermediates. In reactive SDDBDI, the plasma is doped with a reagent before the plasma ions are directed at a cover slip surface bearing another analyte. Different from SDDBDI, reactive SDDBDI can be used both as an ambient ionization source and as a means to produce reagent ions for ambient ion/molecule reactions. The online derivation of 4-aminophenol with trifluoroacetic anhydride demonstrated that reactive SDDBDI can be used for chemical analysis where improved specificity or sensitivity is required. The utility of this approach for real-time detection of reactive intermediate was demonstrated by the Schiff-base and Eberlin reactions. The formed intermediates and products could be readily detected and identified by tandem mass spectrometry. These results indicate that reactive SDDBDI can be used to generate reagent ions that undergo ion/molecule reactions in the open air with an analyte at condensed phase on a surface. Reactive SDDBDI has high-efficiency ion transmission and high MS sensitivity. It is thus a potential tool to perform ambient ion/molecule reactions and detect reactive intermediates.