Soft Argon–Propane Dielectric Barrier Discharge Ionization

Abstract

Dielectric barrier discharges (DBDs) have been used as soft ionization sources (DBDI) for organic mass spectrometry (DBDI-MS) for approximately ten years. Helium-based DBDI is often used because of its good ionization efficiency, low ignition voltage, and homogeneous plasma conditions. Argon needs much higher ignition voltages than helium when the same discharge geometry is used. A filamentary plasma, which is not suitable for soft ionization, may be produced instead of a homogeneous plasma. This difference results in N, present in helium and argon as an impurity, being Penning-ionized by helium but not by metastable argon atoms. In this study, a mixture of argon and propane (CH) was used as an ignition aid to decrease the ignition and working voltages, because propane can be Penning-ionized by argon metastables. This approach leads to homogeneous argon-based DBDI. Furthermore, operating DBDI in an open environment assumes that many uncharged analyte molecules do not interact with the reactant ions. To overcome this disadvantage, we present a novel approach, where the analyte is introduced in an enclosed system through the discharge capillary itself. This nonambient DBDI-MS arrangement is presented and characterized and could advance the novel connection of DBDI with analytical separation techniques such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) in the near future.

Development of an inverse low‐temperature plasma ionization source for liquid chromatography/mass spectrometry

“…All experiments reported in the publications mentioned above were performed using a helium DBD plasma in the ring‐ring‐electrode configuration in a modified APCI source. Another application by Schütz et al used an argon plasma with the addition of propane which proceeds according to chemical ionization (CI) in GC/MS 30 . It seems that the ionization mechanism for a helium DBD plasma is based on the generation of helium metastable species which are capable of ionizing nitrogen by Penning ionization 31 which then leads to the typical APCI mechanism described elsewhere 32 .…”

Modern Plasma‐based Desorption/Ionization: From Atoms and Molecules to Chemical Synthesis

“…There only needs to be reactive species with an ionization potential greater than that of a proton transfer reagent, such as water (12.6 eV) (Snow & Thomas, 1990). Interestingly, proton transfer has been shown to occur in systems where the ions/excited state species from the plasma gas do not have enough energy to ionize water, which indicates that another proton transfer reagent is present (Schütz et al, 2018). In this case, a mixture of argon and propane was used as the discharge gas for a DBD ionization source.…”

“…Protonated propane can act as a proton‐transfer reagent directly or transfer a proton an ambient water molecular to produce H 3 O + because the proton affinity of propane (625.7 kJ/mol) is lower than that of water (691 kJ/mol) (Hunter & Lias, 1998). The argon‐propane DBD source was found to offer five‐ to ten‐fold better sensitivities than APCI when coupled to high‐performance liquid chromatography and a ToF mass analyzer (Schütz et al, 2018).…”

A Critical Review of Recent Progress and Perspective in Practical Denitration Application

“…In the presence of oxygen, if enough reductive gases were added, the decomposition of NO was still dominant. Schütz et al [238] introduced that dielectric barrier discharge can be realized in air atmosphere, discharge uniformly, produce high concentration of isomers, and can be effectively utilized. There are many factors affecting dielectric barrier discharge, such as material of dielectric barrier, discharge voltage, discharge frequency, discharge distance, etc.…”