# Water Modification by Cold Plasma Jet with Respect to Physical and Chemical Properties
## 3 Results and Discussion
### Liquid Treatment--ROS Detection
\begin{table}
\begin{tabular}{c c c} \hline \hline  & \({}^{\bullet}_{2}\)**\({}^{\bullet-}\) (2-OH-E\({}^{+}\)) (nM)** & \(\Delta\)**pH** \\ \hline Plasma-exposed: HE in DDW & 873 \(\pm\) 40 (1745 \(\pm\) 80) & 3 \(\pm\) 0.02 \\ Plasma-non-exposed: HE in DDW & 0 (0) & 0 \(\pm\) 0.02 \\ Plasma-exposed: HE in PBS & 80 \(\pm\) 4 (160 \(\pm\) 8) & 0 \(\pm\) 0.02 \\ Plasma-non-exposed: HE in PBS & 0 (0) & 0 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Plasma generated \({}^{\bullet-}_{2}\) in DDW and PBS; values are averages from 5 repeats, with standard deviation around 5%. The following reactions are given as representative. Apart from the generation/destruction paths of the above-determined radicals, these reactions demonstrate the complicated interplay between the plasma induced species (electrons, photons, radicals, etc.) and the dissolved in the liquid species, which ultimately affect the ion concentration (pH and \(\sigma\)) and the oxidizer concentration (redox) in the liquid. However, the above results are coherent, since a decrease in pH is accompanied by an increase in \(E_{\mathrm{h}}\) and \(\sigma\), with a parallel increase in ROS. \begin{tabular}{c c c c} \hline H\({}_{2}\)O + _hf_ & \(\rightarrow\) & H\({}_{2}\)O\({}^{+}\) + e\({}^{-}\) & (01) \\ H\({}_{2}\)O\({}^{+}\) & \(\rightarrow\) & \({}^{\bullet}\)OH + H\({}^{+}\) & (02) \\ UV + H\({}_{2}\)O & \(\rightarrow\) & H\({}_{2}\)O\({}^{\bullet}\) & (03) \\ UV + H\({}_{2}\)O\({}^{\bullet}\) & \(\rightarrow\) & H\({}^{+}\) + OH\({}^{-}\) & (04) \\ OH\({}^{-}\) & \(\rightarrow\) & \({}^{\bullet}\)OH + e\({}^{-}\) & (05) \\ e\({}^{-}\) + O\({}_{2}\) & \(\rightarrow\) & O\({}_{2}^{\bullet}\) & (06) \\ e\({}^{-}\) + O\({}_{2}\) + H\({}^{+}\) & \(\rightarrow\) & HO\({}_{2}^{\bullet}\) & (07) \\ e\({}^{-}\) + H\({}_{2}\)O & \(\rightarrow\) & \({}^{\bullet}\)OH + \({}^{\bullet}\)H + e\({}^{-}\) & (08) \\ e\({}^{-}\) + H\({}_{2}\)O & \(\rightarrow\) & \({}^{\bullet}\)OH + H + 2e\({}^{-}\) & (09) \\ e\({}^{-}\) + H\({}_{2}\)O & \(\rightarrow\) & \({}^{\bullet}\)H + \({}^{\bullet}\)OH & (10) \\ \({}^{\bullet}\)H + O\({}_{2}\) & \(\rightarrow\) & HO\({}_{2}^{\bullet}\) & (11) \\ O\({}_{2}^{\bullet-}\) + O\({}_{2}^{\bullet-}\) + 2H\({}^{+}\) & \(\rightarrow\) & H\({}_{2}\)O\({}_{2}\) + O\({}_{2}\) & (12) \\ HO\({}_{2}^{\bullet}\) + O\({}_{2}^{\bullet-}\) + H\({}_{2}\)O & \(\rightarrow\) & O\({}_{2}\) + H\({}_{2}\)O\({}_{2}\) + OH\({}^{-}\) & (13) \\ HO\({}_{2}^{\bullet+}\)HO\({}_{2}^{\bullet}\) & \(\rightarrow\) & H\({}_{2}\)O\({}_{2}\) + O\({}_{2}\) & (14) \\ \({}^{\bullet}\)OH + HO\({}_{2}^{\bullet}\) & \(\rightarrow\) & H\({}_{2}\)O\({}^{+}\) + O\({}_{2}\) & (15) \\ OH\({}^{-}\) + O\({}_{2}\) & \(\rightarrow\) & OH\({}^{-}\) + O\({}_{2}\) & (16) \\ H\({}_{2}\)O\({}_{2}\) + \({}^{\bullet}\)H & \(\rightarrow\) & \({}^{\bullet}\)OH + H\({}_{2}\)O & (17) \\ \({}^{\bullet}\)OH + H\({}_{2}\)O\({}_{2}\) & \(\rightarrow\) & HO\({}_{2}^{\bullet}\) + H\({}_{2}\)O & (18) \\ OH + \({}^{\bullet}\)OH & \(\rightarrow\) & H\({}_{2}\)O\({}_{2}\) & (19) \\ \hline \end{tabular}   
Finally, it is noted that participation in the various side reactions of either HO\({}_{2}\)\({}^{\bullet}\) or O\({}_{2}^{\bullet-}\) or both, depends on their pKa (= 4.8 [59]) and on the pH of the unbuffered water, where their molar ratio is determined by the Henderson-Hasselbalch equation, i.e., pH = pKa + log([O\({}_{2}^{\bullet-}\)]/[HO\({}_{2}\)\({}^{\bullet}\)]). Thus, in the unbuffered water, for a pH drop from, e.g., 7 to 5, the molar ratio [O\({}_{2}^{\bullet-}\)]/[HO\({}_{2}\)\({}^{\bullet}\)] changes from about 158 to 1.58.