Microplasma-based flowing atmospheric-pressure afterglow (FAPA) source for ambient desorption-ionization mass spectrometry

Abstract

A new direct-current microplasma-based flowing atmospheric pressure afterglow (FAPA) source was developed for use in ambient desorption-ionization mass spectrometry. The annular-shaped microplasma is formed in helium between two concentric stainless-steel capillaries that are separated by an alumina tube. Current-voltage characterization of the source shows that this version of the FAPA operates in the normal glow-discharge regime. A glass surface placed in the path of the helium afterglow reaches temperatures of up to approximately 400 °C; the temperature varies with distance from the source and helium flow rate through the source. Solid, liquid, and vapor samples were examined by means of a time-of-flight mass spectrometer. Results suggest that ionization occurs mainly through protonation, with only a small amount of fragmentation and adduct formation. The mass range of the source was shown to extend up to at least m/z 2722 for singly charged species. Limits of detection for several small organic molecules were in the sub-picomole range. Examination of competitive ionization revealed that signal suppression occurs only at high (mM) concentrations of competing substances.

Surface Desorption Dielectric-Barrier Discharge Ionization Mass Spectrometry

“…The formation of [M + O + H] + was due to the oxidation of 8-hydroxyquinoline during ionization. Such oxidation reaction was commonly observed for compounds containing the aromatic group in a plasma-based ionization process such as LTP and flowing atmospheric pressure afterglow (FAPA) . No reduction species formed by dihydrogenation was detected.…”

“…Such oxidation reaction was commonly observed for compounds containing the aromatic group in a plasma-based ionization process such as LTP 28 and flowing atmospheric pressure afterglow (FAPA). 29 No reduction species formed by dihydrogenation was detected. This compared well with previous studies in which reduction by dihydrogenation was observed for arenes using LTP but not detected for aromatic heterocycle compounds.…”

Flowing Atmospheric Pressure Afterglow for Ambient Ionization: Reaction Pathways Revealed by Modeling

“…This raises the need for more detailed investigation, e.g., by computer modeling, to reveal the dominant ionization mechanisms. Moreover, it may help to optimize the setup geometry, such as the so-called μ-FAPA . By providing details on the gas flow patterns, computer modeling may, for instance, explain the effect of applying a discontinuous helium gas flow within the FAPA source for the analysis of gaseous samples, leading to lower helium consumption.…”

Laser Desorption/Ablation Postionization Mass Spectrometry: Recent Progress in Bioanalytical Applications

“…Although the plasma‐based techniques share similar chemical and chemi‐ionization reactions, that is, Penning ionization, electron capture/abstraction, and proton transfer, to produce ions from the laser‐desorbed analytes, they are diverse in the configuration of the ion sources, the mechanism of plasma gas discharge, the parameters of the desorption laser, and the way introducing the desorbed species to the ion sources. Due to the metastable/radical‐induced ionization mechanism, the plasma‐based two‐step desorption/ionization methodologies were limited to analysis of molecules with mass weight lower than 1000 Da, but minimization of the size of the discharge chamber has successfully extended the mass range to above 2000 Da (Zeiri et al, 2017). The following sections provide an overview of the plasma‐based postionization techniques and their applications in biological analysis.…”