## 3 Results
### Quantification of the Generated (Reactive) CAP Species
#### 3.1.2 Chemical Composition and pH of CAP Treated Water  
Following 10 min of CAP treatment of a small volume of water, the generated concentrations of H\({}_{2}\)O\({}_{2}\), nitrite, and nitrate were quantified (Figure 3) and the pH of the solution (Figure 4) was determined. Separate ANOVA tests were performed to determine if significant differences were observed between all tested conditions and to examine the influence of a certain plasma characteristic while keeping the other plasma characteristics constant. Based on Figure 3, it can be concluded that H\({}_{2}\)O\({}_{2}\) was only formed at two CAP treatment conditions, i.e., while using the DBD electrode and the highest discharge power at both oxygen levels. As a result, the influence of the plasma characteristics on the formation of H\({}_{2}\)O\({}_{2}\) proved to be rather limited, i.e., the DBD electrode is favored over the SBD electrode at the highest discharge power and the highest discharge power is preferred over the lowest discharge power using the DBD electrode. For the nitrite concentration, all treatment conditions resulted in a significant increase in nitrite compared to the control (blanc). The highest concentration was, however, observed while applying the DBD electrode at the highest discharge power and when oxygen was added to the gas flow. Regarding the influence of the plasma characteristics on the formation of nitrite, it can be concluded that there was no clear correlation between the addition of oxygen and the generation of nitrite since the presence of oxygen either resulted in (i) an increased production of nitrite, (ii) no significant differences, or (iii) a decreased production of nitrite. Generally, higher nitrite concentrations were obtained while using the DBD electrode configuration. Only one exception was observed, i.e., at the highest discharge power and without the addition of oxygen. For this specific case, the opposite trend was observed. Finally, generally higher nitrite concentrations were observed at an increased discharge power. Again, only one exception was observed, i.e., using the DBD electrode without addition of oxygen. The formation  
Figure 2: Generation of UV light monitored using UV-TEC strips (\(n=1\)). All UV-TEC strips, apart from the control, were exposed to CAP for 10 min using each possible combination of plasma characteristics. Afterwards, the color of the (un)treated strips was compared with the provided color scale bars, with each color corresponding to a certain UV intensity (5 = 5 mJ/cm\({}^{2}\) and 10 = 10 mJ/cm\({}^{2}\)). of nitrate was also influenced by the applied treatment characteristics. Some combinations of plasma characteristics did not result in a significant increase compared to the control (blanc), while up to 60 uM nitrate was formed using the DBD-0.0% (_v/v_)-21.88 V. The addition of oxygen generally resulted in a decreased generation of nitrate or no significant differences. Moreover, applying the DBD electrode favored the formation of nitrate, and, while using this specific electrode configuration, an increased nitrate concentration was obtained at an increased discharge power. Figure 3: H\({}_{2}\)O\({}_{2}\), nitrite, and nitrate concentrations (uM) obtained following CAP treatment of 500 uL of sterile water using each possible combination of plasma characteristics (_n_ = 3). Significant differences between all examined conditions (ANOVA test 1) have been indicated by means of a different small letter, with ‘a’ bearing the lowest value. The influence of the oxygen level (ANOVA tests 2–5), the electrode configuration (ANOVA tests 6–9), and the discharge power (ANOVA tests 10–13) on the chemical composition have been indicated as well by means of a different small letter, with ‘a’ again bearing the lowest value. With respect to the pH of the CAP treated water (Figure 4), a significant drop in pH compared to the untreated control was observed for most combinations. Only while using the SBD electrode at the lowest discharge power, this was not the case using both oxygen levels.