# Electrodegradation of Selected Water Contaminants: Efficacy and Transformation Products
## 3 Results and Discussion
### Identification of Transformation Products
#### 3.3.3 Identification of Triton X-100 TPs  
The electrooxidation of t-OPPE was performed only in the Na\({}_{2}\)SO\({}_{4}\) electrolyte based on the experience with BTA and DBP treatment. This is the least corrosive medium of all three and was expected to assist the formation of less problematic TPs. Additionally, the use of a neutral medium eliminated the need to neutralize samples before the analysis.  
Although t-OP, n-OP, n-NP, and their mono- and diethoxylates were expected as the main TPs of t-OPPE after EO, the actual results were different and even surprising. In spite of the fact that 4-_tert_-octylphenol is the main isomer constituting t-OPPE, no build-up of this compound or its monoethoxylate was observed during the course of EO. Instead, their concentration was exponentially decreasing during the EO experiment with a 96% removal of t-OPME in 30 min and 95% removal of t-OP in 45 min, similarly to t-OPPE with 96% removal in 45 min. By comparison, n-OP in n-NP were, in all treated samples, present at very low concentrations and no changes or trends were observed during the time of EO treatment. Therefore, it could be concluded that the degradation rate of intermediate TPs (e.g., t-OPME) is higher or approximately the same as the degradation rate of the parent compound.  
These findings imply that other TPs should be formed either as intermediates in the degradation of t-OPPE to t-OPME and further to t-OP, as well as other TPs produced from t-OP degradation. A careful inspection of LC-MS chromatograms revealed peaks for two unknown TPs which reached the highest concentration after 30 and 15 min of EO, respectively. The mass spectrum of the unknown TP peaking at 15 min of EO is shown in Figure 8.  
Comparison with the literature [53; 54] revealed that the intermediate TP at 30 min is probably an oxyacetaldehyde derivative of alkylphenol ethoxylates, while the TP at 15 min could be alkylphenol carboxylic acid.  
Figure 8: TIC mass spectrum of TP peaking at 15 min of EO (\(m/z\) range 550–740), LC-MS, ESI+ mode.  
In addition to these main TPs, there were several other novel peaks in the chromatogram, but with lower intensity. Some of these TPs were tentatively identified as being the same as those detected with the photocatalysis of t-OPPE [55] and are shown in Table 5.  
Furthermore, GC-MS chromatograms of samples after EO treatment were also inspected for the possible new peaks signifying TPs. However, it should be noted that extraction and derivatization was performed prior to GC-MS analysis, which could cause a loss of unknown TPs, in spite of BSTFA also forming volatile derivatives with other functional groups in addition to phenolic groups, e.g., carboxylic groups.  
In other experiments with EO on similar substances [40; 56], a degradation mechanism via hydroquinone was proposed, leading to the formation of low-chain carboxylic acids, such as fumaric and maleic acid, and further, to complete mineralization. In the chromatograms of our samples, a peak corresponding to derivatized fumaric/maleic acid (isomers) was noticed (Figure 9), but not for hydroquinone which was probably not derivatized and was eluted at completely different GC conditions.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \(m/z\) **Values** & **Adduct** & **Structure of TP** \\ \hline
569.4; 613.4; 657.4; 701.4 & [M+K]\({}^{+}\) & \\
572.4; 616.4; 660.4; 704.4 & [M+acetonitrile+H] \({}^{+}\) & \\ \hline
572.4; 616.4; 660.4; 704.4 & [M+Na]\({}^{+}\) & \\
569.4; 613.4; 657.4; 701.4 & [M+acetonitrile+Na] \({}^{+}\) & \\ \hline
574.4; 618.4; 662.4; 706.4 & [M+Na]\({}^{+}\) & \\
593.4; 637.4; 681.4; 725.4 & [M+acetonitrile+H] \({}^{+}\) & \\ \hline
587.4; 631.4; 675.4; 719.4 & [M+acetonitrile+Na] \({}^{+}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Proposed minor TPs of t-OPPE from LC-MS spectra.  
Figure 9: Enlarged GC-MS spectrum of a peak corresponding to derivatized fumaric/maleic acid (\(m/z\) range 100–400).