Soft ionization mechanisms in flexible µ-tube plasma – elucidation of He-, Ar-, Kr-, and Xe-FµTP
Abstract
The soft ionization mechanism of helium-based plasma seems to be understood while it still remains challenging in argon-based plasma, although many studies have used argon plasmas as a soft ionization source with good ionization efficiencies. In this study, helium, argon, krypton, and xenon were fed into the same discharge geometry, a flexible micro-tube plasma (F mu TP), to determine the ionization mechanisms. The F mu TPs operated with the named noble gases obtained comparable ionization efficiencies by MS measurements. The optical emission results showed that N2+ were the dominant ions within the helium-F mu TP and noble gas ions were dominant for the other plasmas. These ions support the development of excitation and eventually stop at the end of the capillary. Therefore, Penning ionization and charge transfer between plasma and ambient air/analytes in the open atmosphere have been proven not to be the primary soft ionization mechanism. Furthermore, it was found that photoionization played a minor role in soft ionization. Using helium as a diagnosis gas in front of the discharge capillary nozzle of the F mu TP, where the sample is usually positioned, shows that helium can be ignited by all of these F mu TPs. This demonstrates that the excitation of a diagnosis gas as well as the ionization of analytes is independent of the type of the discharge gas. An alternative mechanism that a transient potential created by the ions is responsible for the soft ionization is subsequently proposed. Show more
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https://doi.org/10.3929/ethz-b-000685570Publication status
publishedExternal links
Journal / series
Analytical and Bioanalytical ChemistryVolume
Pages / Article No.
Publisher
SpringerSubject
Flexible μ-tube plasma (FμTP); Noble gas ions; Mechanisms of soft ionizationRelated publications and datasets
Is referenced by: https://doi.org/10.3929/ethz-b-000702401
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