Although electron impact ionization (EI) remains the standard ionization source for GC-MS, it presents extensive fragmentation as its main limitation. The potential of a novel plasma-based soft ionization source named controlled-atmosphere flexible microtube plasma (CA-F mu TP) has been evaluated in this work for the determination of monoaromatic volatile BTEX group (namely benzene, toluene, ethylbenzene, and o-, m- and p-xylenes) in olive oil, based on headspace technique. The obtained results show an attractive advantage over EI due to no fragmentation was observed. A nitrosated ion [M + NO](+) is obtained as the most abundant species. Thus, the BTEX mass spectrum identification can be carried out without major effort. In general, the sensitivity for CA-FmTP was comparable to those obtained by EI, achieving LODs ranged from 0.6 to 1.0 mu g kg(-1). The potential usefulness of GC-CA-F mu TP-MS for the detection of BTEX was demonstrated by analyzing olive oil samples and identifying traces of these compounds in one sample. Therefore, the proposed plasma-based soft ionization is suitable for BTEX analysis in fatty complex matrixes as olive oil. (C) 2021 Published by Elsevier B.V.

A new soft ionization device for mass spectrometry is presented using the flexible microtube plasma under controlled atmospheric conditions. The controlled atmosphere flexible microtube plasma consists of the plasma source itself connected to a gas chromatograph and a mass spectrometer using a borosilicate glass cross piece. Controlled atmosphere, for example, nitrogen and/or an oxygen mixture, is introduced to the system to create a clean ionization environment. Reproducibility issues are discussed, and solutions are presented manipulating the gas flow in the cross piece. A proof of concept is shown using a ketone mixture introduced to the mass spectrometer to optimize atmospheric conditions. Furthermore, application of the presented device for the sensitive and nonfragmenting ionization of volatile organic biomarkers relevant for cancer is carried out. Sample treatment for human saliva is described, and relevant candidate biomarkers are measured in the saliva matrix, showing a very good ionization efficiency and neglectable matrix effects with limits of detection below 80 ppt.

In this study, a two-dimensional axi-symmetric model has been developed in order to shed light into the evolution of a He and He/O2 capillary plasma jet. The plasma jet interacts with a dielectric surface placed normal to the jet axis to bring the model closer to applications. This work examines, from first principles, the shape and speed of the of the plasma bullet, the intensity of the induced electric (IEF) field on the dielectric surface and the underlying dominant chemical reactions of the plasma. Furthermore, the work provides insight and understanding into the mechanisms behind many experimental observations such as the torus (or donut) and sphere plasma bullet shapes for pure Helium and He/O2 plasma, respectively.

Plasma sources in atmospheric pressure soft-ionization mass spectrometry have gained significant interest in recent years. As many of these sources are used under ambient air conditions, their interaction with the surrounding atmosphere plays an important role in the ionization pathway. This study focuses on the interaction between the plasma source and the surrounding atmosphere by connecting the plasma source to the mass spectrometer using a 2 mm ID closed reactant capillary supplied by a reactant gas up to 500 mL per minute to gain a controlled atmosphere. Different reactant gases (Ar, He, O2, and N2) and reactant gas mixtures are tested with regard to the DBDI performance and then used to improve the ionization efficiency. Tailoring the controlled atmosphere for a certain analyte, for example, perfluorinated compounds, leads to significantly improved limits of detection up to 2 ppb.

Dielectric barrier discharges are used as soft ionization sources for mass spectrometers or ion mobility spectrometers, enabling excellent possibilities for analytical applications. A new robust and small-footprint discharge design, flexible microtube plasma (FμTP), developed as a result of ongoing miniaturization and electrode design processes, is presented in this work. This design provides major safety benefits by fitting the electrode into an inert flexible fused silica capillary (tube). Notably, in this context, the small discharge dimensions enable very low gas flows in the range of <100 mL min-1; portability; the use of hydrogen, nitrogen, and air in addition to noble gases such as helium and argon, including its mixtures with propane; and application in microchip environments. By coupling FμTP with gas chromatography/mass spectrometry, we show that the polarity principle of the new discharge design allows it to outperform established ionization sources such as dielectric barrier discharge for soft ionization (DBDI) and low-temperature plasma (LTP) at low concentrations of perfluoroalkanes in terms of sensitivity, ionization efficiency, chemical background, linear dynamic range, and limit of detection by a large margin. In negative ion mode, the limit of detection is improved by more than 3-fold compared with that of DBDI and by 8-fold compared with that of LTP. The protonation capability was evaluated by headspace measurements of diisopropyl methylphosphonate in positive ion mode, showing low fragmentation and high stability in comparison to DBDI and LTP.

Dielectric barrier discharges (DBDs) are well-established and useful tools for scientific as well as industrial applications. They have been of high interest for analytical applications due to the fact that DBDs can produce small, low temperature/power, and atmospheric plasmas. These kind of plasmas can be applied for the detection and quantification of analytes in several ways: either, DBDs can be used for example as fragmentation and excitation sources to detect elements via optical emission spectrometry (OES), or as ionization sources of molecules for the detection via mass spectrometry (MS). ISAS has developed several of these discharges and studied the impact of the DBD itself on the subsequent application. This work summarizes the development from low pressure DBD implemented in diode laser atomic absorption spectrometry to atmospheric DBDs that can be used for different ambient applications such as the trace detection of arsenic species via OES or the soft ionization of molecular compounds via MS.

Dielectric barrier discharge (DBD)-based analytical applications have experienced rapid development in recent years. DBD designs and parameters and the application they are used for can vary considerably. This leads to a diverse field with many apparently unique systems that are all based on the same physical principle. The most significant changes among DBDs used for chemical analysis are in how the discharge electrodes are separated from the ignited discharge gas. While the official definition of a DBD states that at least one electrode has to be covered by a dielectric to be considered a DBD, configurations with both electrodes covered by dielectric layers can also be realized. The electrode surface plays a major role in several plasma-related technical fields, surface treatment or sputtering processes, for example, and has hence been studied in great detail. Analytical DBDs are often operated at low power and atmospheric pressure, making a direct transfer of insight and know-how gained from the aforementioned well-studied fields complicated. This work focuses on comparing two DBD configurations: the low temperature plasma probe (LTP) and the dielectric barrier discharge for soft ionization (DBDI). The LTP is representative of a DBD with one covered electrode and the DBDI of a design in which both electrodes are covered. These two configurations are well suited for a systematic comparison due to their similar geometric designs based on a dielectric capillary.