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; 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.
The soft ionization ability based on plasma-jet protonation of molecules initiated by a dielectric barrier discharge ionization source (DBDI) is certainly an interesting application for analytical chemistry. Since the change of an applied sinusoidal voltage may lead to different discharge modes the applied discharge was powered by a square wave generator in order to get a homogeneous plasma. It is known that besides the protonation [M+H](+) of unpolar as well as some polar molecules the homogeneous DBDI can be used to ionize molecules directly [M](+). Here we prove that the DBDI can be applied to exchange fluorine by oxygen of perfluorinated compounds (PFC). PFC are organofluorine compounds with carbon-fluorine and carbon-carbon bonds only but no carbon-hydrogen bonds. While the position of the introduction into the plasma-jet is essential, PFC can be measured in the negative mass spectrometer (MS) mode.
This study introduced sandwich-structured copperglass substrates for standardization of laser desorption and plasma ionization. For standardized quantitative analysis, cavities were constructed which allow better reproducibility in droplet deposition and for laser application. Applying the diode laser, molten substrate material is incorporated into the glass, being trapped inside. Therefore, this method can be separated from laser ablation, achieving high ion signals without ablating material from the surface. Flexible microtube plasma (FμTP) was selected as the ionization source, this being the first time that laser desorption and FμTP ionization are coupled. This laser−plasma interface was applied to the detection of cholesterol, which showed a significantly improved limit of detection of 0.46 ng and linear dynamic range of 3 orders of magnitude in positive ion mode compared to other (ambient air mass spectrometry) methods. The main reason was the change of phase on the copper surface. The dehydrated molecule [M-H 2 O+H] + was the base peak of the spectrum and no further dissociation or fragmentation was observed. Blood plasma was spiked with cholesterol. In a 1:100 chloroform dilution, the presence of the plasma was neglectable and led to the same detection limits and linear dynamic range as in the cholesterol standard. No sample preparation or internal standards were needed for calibration. The physical effects of the surface modification were investigated, including the calculation of the laser beam waist to simplify the comparison and reproducibility of results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.