Hydroxyl radical densities in plasma treated liquid

Hydroxyl radical concentrations in plasma treated liquid are measured using two different techniques: electron paramagnetic resonance (EPR) spectroscopy [1] and a terephthalic acid (TA) assay [2]. A COST Reference Microplasma Jet [3] is used with a variety of treatment durations, applied voltages, and helium based gas mixtures. As one of the most prominent radicals, $^{\mathrm{\bullet }}$OH is primarily produced through dissociative collisions with high energy electrons and metastables in the active plasma and jet effluent [4]. OH radicals are potent oxidizers and precursors to hydrogen peroxide and other reactive oxygen species important for biomedical applications. The source of $^{\mathrm{\bullet }}$OH in the plasma treated liquid is also identified using isotopic admixtures in the feed gas. [1] Y. Gorbanev et al., \textit{Phys. Chem. Chem. Phys.}, \textbf{4}, 2018 [2] S. Kanazawa et al., \textit{Int. J. Plasma Environ. Sci. Technol.}, \textbf{6}, 2012 [3] J. Golda et al., \textit{J. Phys. D: Appl. Phys.,} \textbf{49}, 2016 [4] J. Benedikt et al., \textit{Plasma Sources Sci. Technol.,}~\textbf{25,}~2016