Investigation of ion formation generated by an easy-to-assemble dielectric barrier discharge plasma ionization source based on printed circuit boards

This study presents a detailed investigation of a recently developed dielectric barrier discharge plasma ionization source based on printed circuit boards. Specifically, the reactant and product ions formed in positive and negative polarity, and the difference, when the analyte is guided through or bypasses the plasma of the developed plasma ionization source, were investigated. Therefore, the ionization source is coupled to a self-built ion mobility spectrometer coupled to a mass spectrometer to obtain detailed ion mobility and m / z information. As test compounds, 2-propanol, 2-butanol, 2-pentanol, 2-propanone, sevoflurane, desflurane, and dibutyl maleate were used. We identified the dominant reactant ion species as protonated water clusters (H⁺(H₂O)_n) in positive mode and nitrate clustered with nitric acid NO₃⁻(HNO3)₂ in negative mode, yielding well-defined ion chemistry conditions. When the analytes are directed through the plasma, there is no fragmentation due to soft ionization, but a significant change in plasma chemistry, e.g. the alcohols tested show a significant conversion to the corresponding ketones (by oxidative dehydrogenation), which was the dominant pathway when they were passed directly through the plasma.