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Speicher L, Song H, Ahlmann N, Foest D, Höving S, Brandt S, Niu G, Franzke J, Tian C. Soft ionization mechanisms in flexible µ-tube plasma-from FµTP to closed µ-tube plasma. Anal Bioanal Chem 2024; 416:4919-4927. [PMID: 38958704 DOI: 10.1007/s00216-024-05420-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 05/29/2024] [Accepted: 06/24/2024] [Indexed: 07/04/2024]
Abstract
In order to find an explanation for the mechanism in a plasma operated with an alternating voltage, or rather a square wave voltage, such a plasma was investigated. It was found that Penning ionization, charge transfer, and photoionization played a minor or even no role in the soft ionization mechanism of a FµTP. If the collision of plasma gases with air does not contribute to soft ionization, it should also be possible to use a separated plasma for soft ionization. Preliminary investigations show that it is possible to ignite a diagnosis gas with a plasma gas even when there is a barrier such as glass between those gases. A temporally and locally limited potential must be produced at the outer surface to achieve this. This potential should be sufficient to ionize the environment softly and to be able to use this so-called closed µ-tube plasma as a new ionization source.
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Affiliation(s)
- Luisa Speicher
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Hao Song
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Norman Ahlmann
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Daniel Foest
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Simon Höving
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Sebastian Brandt
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Guanghui Niu
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093, Zurich, Switzerland
| | - Joachim Franzke
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany.
| | - Caiyan Tian
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany.
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Tian C, Song H, Ahlmann N, Brandt S, Foest D, Niu G, Franzke J, Speicher L. Soft ionization mechanisms in flexible µ-tube plasma-elucidation of He-, Ar-, Kr-, and Xe-FµTP. Anal Bioanal Chem 2024; 416:4907-4918. [PMID: 39004680 DOI: 10.1007/s00216-024-05419-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 05/29/2024] [Accepted: 06/24/2024] [Indexed: 07/16/2024]
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 (FµTP), to determine the ionization mechanisms. The FµTPs 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-FµTP 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 FµTP, where the sample is usually positioned, shows that helium can be ignited by all of these FµTPs. 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.
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Affiliation(s)
- Caiyan Tian
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Hao Song
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Norman Ahlmann
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Sebastian Brandt
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Daniel Foest
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany
| | - Guanghui Niu
- Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093, Zurich, Switzerland
| | - Joachim Franzke
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany.
| | - Luisa Speicher
- Leibniz-Institute for Analytical Sciences - ISAS - eV., Bunsen-Kirchhoff-Straße 11, 44139, Dortmund, Germany.
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Ayala-Cabrera JF, Montero L, Sahlabji T, Schmitz OJ. Comprehensive two-dimensional gas chromatography with flow modulator coupled via tube plasma ionization to an atmospheric pressure high-resolution mass spectrometer for the analysis of vermouth volatile profile. Anal Bioanal Chem 2023; 415:2561-2573. [PMID: 37059842 PMCID: PMC10149472 DOI: 10.1007/s00216-023-04688-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 04/03/2023] [Accepted: 04/03/2023] [Indexed: 04/16/2023]
Abstract
The analysis of complex samples is a big analytical challenge due to the vast number of compounds present in these samples as well as the influence matrix components could cause in the methodology. In this way, comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC × GC-MS) is a very powerful tool to achieve the characterization of complex samples. Nevertheless, due to possible coelutions occurring in these matrices, mixed spectra are generally obtained with electron ionization (EI) which could extremely complicate the identification of the analytes. Thereby, new methodology setups are required to improve the confidence on the identification in non-targeted determinations. Here, we present a high-throughput methodology consisting of GC × GC with flow modulation coupled to high-resolution atmospheric pressure mass spectrometry (HRMS) via a novel tube plasma ion source (TPI). The flow modulator allows to easily automate the GC × GC method compared to traditional cryo-modulators, while the soft ionization provided by TPI helps to preserve the [M]+• or [M+H]+ ions, thus increasing the confidence in the identification. Additionally, the combination of a flow modulation with an atmospheric pressure mass spectrometer significantly improves the sensitivity over flow modulated GC × GC-EI-MS methods because no split is required. This methodology was applied to the analysis of a complex sample such as vermouth where the volatile profile is usually considered by consumers as a product quality indicator since it raises the first sensations produced during its consumption. Using this approach, different classes of compounds were tentatively identified in the sample, including monoterpenes, terpenoids, sesquiterpenoids and carboxylic acid, and carboxylate esters among others, showing the great potential of a GC × GC-TPI-qTOF-MS platform for improving the confidence of the identifications in non-targeted applications.
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Affiliation(s)
- Juan F Ayala-Cabrera
- Applied Analytical Chemistry, University of Duisburg-Essen, Universitatsstr. 5, D-45141, Essen, Germany
- Teaching and Research Center for Separation, University of Duisburg-Essen, Universitatsstr. 5, 45141, Essen, Germany
| | - Lidia Montero
- Applied Analytical Chemistry, University of Duisburg-Essen, Universitatsstr. 5, D-45141, Essen, Germany
- Teaching and Research Center for Separation, University of Duisburg-Essen, Universitatsstr. 5, 45141, Essen, Germany
| | - Taher Sahlabji
- Department of Chemistry, College of Science, King Khalid University, P.O. Box 9004, Abha, 61413, Saudi Arabia
| | - Oliver J Schmitz
- Applied Analytical Chemistry, University of Duisburg-Essen, Universitatsstr. 5, D-45141, Essen, Germany.
- Teaching and Research Center for Separation, University of Duisburg-Essen, Universitatsstr. 5, 45141, Essen, Germany.
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Isomer analysis by mass spectrometry in clinical science. Trends Analyt Chem 2022. [DOI: 10.1016/j.trac.2022.116907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Ayala-Cabrera JF, Montero L, Meckelmann SW, Uteschil F, Schmitz OJ. Review on atmospheric pressure ionization sources for gas chromatography-mass spectrometry. Part I: Current ion source developments and improvements in ionization strategies. Anal Chim Acta 2022; 1238:340353. [DOI: 10.1016/j.aca.2022.340353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 08/24/2022] [Accepted: 09/02/2022] [Indexed: 11/26/2022]
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Ayala-Cabrera JF, Montero L, Meckelmann SW, Uteschil F, Schmitz OJ. Review on atmospheric pressure ionization sources for gas chromatography-mass spectrometry. Part II: Current applications. Anal Chim Acta 2022; 1238:340379. [DOI: 10.1016/j.aca.2022.340379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 09/06/2022] [Accepted: 09/07/2022] [Indexed: 11/26/2022]
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