Production of TEMPO by O atoms in atmospheric pressure non-thermal plasma–liquid interactions

Non-thermal atmospheric pressure plasmas enable plasma treatment of surfaces without requiring a low-pressure environment. These plasmas are currently of interest for, among other things, their biomedical applications, many of which are enabled by production of reactive oxygen and nitrogen species (RONS). Plasma–liquid interactions are especially important due to the high amounts of water in biological materials. However, the chemistries of these plasmas are very complex and are not well-understood. One method to quantify plasma–liquid interactions is to dissolve a reactant into the liquid which, when exposed to plasma-created RONS, forms a measurable product. In particular, the oxidation of the spin trap TEMP to TEMPO has been used to track trends in reactive oxygen species. However, the effect of individual species on TEMP has not previously been determined. This paper differentiates the oxidation of TEMP due to various oxygen species produced by a He plasma jet operating in a controllable environment. Oxidation of TEMP is mainly to O atoms, with small or negligible contributions from other species. Thus, the TEMPO yield will also be used to illuminate trends in O atom production.