# Electrodegradation of Selected Water Contaminants: Efficacy and Transformation Products
## 3 Results and Discussion
### Identification of Transformation Products
#### 3.3.2 Identification of Dibutyl Phthalate's TPs  
Based on the experience of EO experiments on BTA, the TPs' identification was performed only in sodium sulphate medium (2 g/L, conductivity 3 mS/cm). Although the degradation proceeded faster at acidic pH in H\({}_{2}\)SO\({}_{4}\) medium (see Table 2), we decided to use Na\({}_{2}\)SO\({}_{4}\) as a less corrosive medium forming presumably similar reactive species. The use of neutral medium eliminated the need to neutralize samples before the analysis. While the degradation of DBP was obvious, there were many extraneous chromatographic peaks present in the chromatogram and the relevant signals had to be identified by comparison with chromatograms of untreated samples. An example of a chromatogram of an EO-treated sample is shown in the Supplementary Materials (Figure S4).  
The structure of TPs was tentatively identified from low-resolution MS/MS product ion spectra--LRMS PIS (initial ionisation both in ESI+ and ESI\(-\)), as well as from high-resolution MS spectra obtained with the TOF instrument--HRMS (ESI+ and ESI\(-\)). Table 4 shows the results of the latter and the proposed chemical formulae, while Figure 7 depicts the proposed structural formulae. As seen from Table 4, several different peaks were elucidated as the same TP, because some TPs formed adducts with Na\({}^{+}\), ACN, formiate, etc.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **m/z** \\ **(HRMS** \\ **ESI+)** \\ \end{tabular} & \begin{tabular}{c} **Theoretical** \\ **Molar Mass** \\ \end{tabular} & \
\begin{tabular}{c} **Mass Error** \\ **[ppm]** \\ \end{tabular} &
\begin{tabular}{c} **Proposed** \\ **Formula** \\ \end{tabular} & **Annotation * & **Confirmation** \\ \hline \hline \multirow{4}{*}{279.1601 **} & \multirow{4}{*}{279.1596} & \multirow{4}{*}{1.79} & \multirow{4}{*}{[C\({}_{16}\)H\({}_{22}\)O\({}_{4}\)+H]\({}^{*}\)} & \multirow{4}{*}{a **} & LRMS PIS \\  
Several papers dealing with the EO of DBP on different anode materials and in different electrolytes have already been published and were reviewed by [PERSON] et al. [7]. Only some of these papers go beyond the monitoring of parent compound degradation and also identify the transformation products. According to these, the main electrochemical degradation pathways in non-chloride media include dealkylation, hydroxyl addition, decarboxylation, and the cleavage of the benzene ring [7]. Identified TPs in these studies were mono- or polyhydroxylated DBP, monobutyl phthalate, phthalic acid, hydroxphthalic acids, phthalic anhydride, hydroxybenzoic acids, mono-, di-, and tri-hydroxybenzene, and several aliphatic carboxylic acids [7]. In our study, we found mainly the initial TPs formed by dealkylation and hydroxyl addition, but not the more progressive TPs. Such findings presumably result from two main causes: (i) the treatment time was not long enough and (ii) the applied analytical methods were not suitable for the detection of very polar progressive TPs such as polyhydroxybenzenes and aliphatic carboxylic acids. In particular, the latter are usually determined by ion chromatography [40].