Dynamic analysis of reactive oxygen nitrogen species in plasma-activated culture medium by UV absorption spectroscopy

The liquid-phase chemical kinetics of a cell culture basal medium during treatment by an argon-fed, non-equilibrium atmospheric-pressure plasma source were investigated using real-time ultraviolet absorption spectroscopy and colorimetric assays. Depth- and time-resolved NO2- and NO3- concentrations were strongly inhomogeneous and primarily driven by convection during and after plasma-liquid interactions. H₂O₂ concentrations determined from deconvolved optical depth spectra were found to compensate for the optical depth spectra of excluded reactive species and changes in dissolved gas content. Plasma-activated media remained weakly basic due to NaHCO₃ buffering, preventing the H⁺-catalyzed decomposition of NO2- seen in acidic plasma-activated water. An initial increase in pH may indicate CO₂ sparging. Furthermore, the pH-dependency of UV optical depth spectra illustrated the need for pH compensation in the fitting of optical depth data.