Monitoring of the electrochemical oxidation of venlafaxine and its metabolite o- desmethylvenlafaxine using a flow cell and high-resolution mass spectrometry

Monitoring of the electrochemical oxidation of venlafaxine and its metabolite o- desmethylvenlafaxine using a flow cell and high-resolution mass spectrometry | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Monitoring of the electrochemical oxidation of venlafaxine and its metabolite o- desmethylvenlafaxine using a flow cell and high-resolution mass spectrometry Melanie Voigt, Jean-Michel Dluziak, Nils Wellen, Victoria Langerbein, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6079652/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Jul, 2025 Read the published version in Environmental Sciences Europe → Version 1 posted 10 You are reading this latest preprint version Abstract Background The antidepressant venlafaxine and its metabolite o-desmethylvenlafaxine are frequently found in water bodies around the world reaching several micrograms per liter. As a remedy, electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation with a boron doped diamond (BDD) electrode have proven to be a suitable means to prevent entrance in the aquatic environment. For potential application, optimization of the EAOPs can be readily achieved by variation of the conditions using a flow cell as compared to a batch-mode cell. Monitoring and characterization of the reactants provide inside into the oxidation mechanism. Results High performance liquid chromatography and high-resolution mass spectrometry led to the observation of five transformation products of venlafaxine and to four of o-desmethylvenlafaxine. Mass voltammograms were recorded from which the impact of the oxidation conditions on the degradation and the quantity and nature of transformation products were derived. The transformation pathways were identified as well. Detailed analysis revealed that hydroxyl radicals played the major role in the electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine. The prevalence of the hydroxyl radical induced degradation was further corroborated by the radical scavenger tert -butanol, causing a decrease in elimination efficiency. Both drugs were best eliminated at pH 3 and a voltage of 1.5 V, with the least ecotoxicological concern as indicated by QSAR analysis. Conclusion The study shall contribute to the advancement of EAOPs for advanced stages in wastewater purification treatment. An in silico ecotoxicity assessment using QSAR analysis showed that electrochemical oxidation is beneficial from an ecotoxicological point of view. Especially products formed via the indirect hydroxyl radical-induced mechanism showed a lower ecotoxicity than the initial compound. Electrochemical advanced oxidation processes (EAOPs) HPLC-HRMS electrochemical oxidation electrolysis flow cell boron-doped diamond electrode EU watchlist Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Highlights Five products were detected by HRMS during the electrochemical oxidation of venlafaxine. Four new products were identified during the electrochemical oxidation of o-desmethylvenlafaxine by HRMS analysis. The indirect mechanism dominates the electrochemical oxidation. The addition of sulfuric acid favors the electrochemical oxidation only slightly. In silico ecotoxicity assessment showed that most transformation products were less toxic than the initial drug substance. Background Venlafaxine is used as an antidepressant medicine. It is applied as a prodrug of its main active metabolite o-desmethylvenlafaxine (Dean, 2012 ; Eh-Haj, 2021 ). Due to its frequent prescription, venlafaxine and its metabolites n-desmethylvenlafaxine, o-desmethylvenlafaxine n,n-didesmethylvenlafaxine and n,o-didesmethylvenlafaxine are regularly detected in various waters at concentrations up to 590 µg/L (Dusi et al., 2019 ). In surface water, venlafaxine was observed at 400 µg/L in Argentina and at 2.61 µg/L in the United States (Dusi et al., 2019 ). Like many pharmaceuticals, venlafaxine and its metabolites cannot be completely eliminated from wastewater through the three common purification stages of conventional waste water treatment plants (WWTPs), i.e. the mechanical, biological and chemical stages and were regular found in effluents (Dusi et al., 2019 ; Kilpinen et al., 2024 ; Kosma et al., 2020 ; Lin et al., 2021 ). Hence WWTPs act as the main entry routes of many pharmaceuticals. Since sufficient data on the prevalence of some substances in the aquatic environment are not available, the European Union introduced a watchlist of substances to be monitored across the European Union in the field of water policy according to Article 8b of the Directive 2008/105/EC (European Commission, 2015 ) in 2015. The list is updated every few years. The substances venlafaxine and o-desmethylvenlafaxine investigated in this study appeared on the third and remain on the current fourth EU watchlist (European Commission, 2022 , 2020 ). Venlafaxine has a negative effect on the aquatic environment. It has already been shown to affect the gene expression of salmon, as well as reducing the serotonin concentration in the brain of hybrid striped bass and impairing their hunting behavior (Bisesi et al., 2014 ; Hodkovicova et al., 2020 ). It can also lead to the isolation of the feet of freshwater snails, conches and other mollusks (Fong and Molnar, 2013 ). In order to minimize a potential threat to the aquatic environment and to eliminate pharmaceuticals from WWTP effluents, research has been conducted on various advanced processes for several years to extend the conventional purification stages. These include advanced oxidation processes (AOPs), such as the use of ozone or UV irradiation (Coha et al., 2021 ; Voigt et al., 2020 ; Wang and Wang, 2021 ). Common feature of AOPs is the formation and chemistry of hydroxyl radicals (HO • ). Hence electrochemical oxidation belongs to the AOPs. Due to their high standard oxidation–reduction potential of 2.8V, HO • are often able to mineralize organic substances such as pharmaceuticals and other anthropogenic micropollutants (Chaplin, 2014 ; Moreira et al., 2017 ). Various electrodes, such as boron-doped diamond (BDD), glassy carbon, titanium dioxide (TiO 2 ) and lead dioxide (PbO 2 ), are being investigated for their suitability for electrochemical oxidation processes (Wang and Zhuan, 2020 ). The BDD electrodes proved particularly efficient and were found the most non-active anode suitable for anodic oxidation (Chaplin, 2014 ; Lozano et al., 2022 ; McBeath et al., 2019 ; Moreira et al., 2017 ). Micropollutants R are oxidized directly by electron transfer to the BDD electrode, cf. Eq. 1, with the stoichiometric coefficients x and y (Moradi et al., 2020 ). An electrochemical oxidation transfer reaction (EOTR) occurs at voltages higher than 1.23 V (Kapałka et al., 2007 ). Here, hydroxyl radicals are generated from water discharge at the anodic active side of the BDD electrode, see Eq. 2. The hydroxyl radicals oxidize and eventually mineralize the micropollutants completely, cf. Eq. 3, The mineralization reaction competes with the anodic discharge of the hydroxyl radicals to molecular oxygen, cf. Eq. 4. R + x(e − )BDD → xBDD + Mineralization products + yH + + ye − (1) BDD + H 2 O → BDD(.OH) + H + + e − (2) R + x(.OH)BDD → xBDD + Mineralization products + yH + + ye − (3) BDD(.OH) → BDD + \(\:\frac{1}{2}\) O 2 + H + + e − (4) Additives such as sulfuric acid or hydrochloric acid can further promote degradation (Sirés et al., 2014 ). These acids increase the conductivity, change the pH and intensify the formation of reactive oxygen species, thus augmenting the degradation efficiency. Furthermore, persalts or Fenton reagents are well known for enhancing electrochemical oxidation (Voigt and Jaeger, 2024 ; Wang et al., 2022 ). The degradation kinetics of venlafaxine were also investigated at different conditions, where an increase in current density was found to accelerate the degradation (Yu et al., 2022 ). The addition of sulfuric acid, ammonia and tert -butanol may induce different oxidation mechanisms. Two main mechanisms have been reported in the absence of such additives: the direct pathway, where a substance is degraded directly by electron transfer and oxidation, and the indirect pathway where hydroxyl radicals are formed by electrochemical oxidation of water and the substance is oxidized through the radicals (Moreira et al., 2017 ; Sirés et al., 2014 ; Voigt et al., 2024 ). Addition of sulfuric acid leads to two additional reaction mechanisms. On the major pathway, hydroxyl radicals generate sulfate radicals, see Eqs. 5 and 6 depending on the pH (Bessegato et al., 2019 ; Davis et al., 2014 ). The secondary sulfate radicals induce the elimination of the substance. The second sulfate pathway results in the direct formation of sulfate radicals at the BDD electrode, see equations 6 and 7, while the recombination of two sulfate radicals is possible leading to the peroxy species, cf. Eq. 8 (Farhat et al., 2015 ). H 2 SO 4 + .OH→ \(\:{\text{S}\text{O}}_{4}^{·-}\) +H 3 O + (5) HS \(\:{\text{O}}_{4}^{-}\) + .OH→ \(\:{\text{S}\text{O}}_{4}^{·-}\) +H 2 O (6) \(\:{\text{S}\text{O}}_{4}^{2-}+\text{B}\text{D}\text{D}\:\) → \(\:{\text{B}\text{D}\text{D}(\text{S}\text{O}}_{4}^{·-})\) +e − (7) \(\:{\text{S}\text{O}}_{4}^{·-}+{\text{S}\text{O}}_{4}^{·-}\) → \(\:{\text{S}}_{2}{\text{O}}_{8}^{2-}\) (8) Radical scavengers, such as tert -butanol, capture the hydroxyl radicals and thus decelerate the electrochemical oxidation (Chen et al., 2018 ). The mechanism is shown in Fig. 1 . Two tert -butanol molecules scavenge two hydroxyl radicals leading to the formation of water and, since the tert -butyl radicals are less reactive, to recombination (Ulanski and von Sonntag, 1999 ). Recently, a mechanism leading to tert-butyl peroxyl radicals, when oxygen is present in solution, has been discussed, with the latter radicals being also less reactive (Gao et al., 2021 ). For the addition of ammonia, several mechanisms for the BDD-electrochemical oxidation have been described, cf. Figure 1 and equations 9 and 10 (Michels et al., 2010 ). NH 3 →.NH 2 + H + +e − (9) 2NH 3 →N 2 + 6H + +6e − (10) The different mechanisms cause different products with different ecotoxic potential. Since electrochemical oxidation reactions often yield a mixture of products, whose ecotoxicological hazard may prove difficult to assess in vivo , in silico methods, such as quantitative structure-activity relation (QSAR) analysis, are often used to predict the ecotoxicity of individual substances using mathematical models (Voigt and Jaeger, 2023 ). In a preceding study, the BDD-electrochemical degradation of venlafaxine was investigated in a synthesis cell at a constant voltage of 1.5 V under various conditions, such as the addition of hydrogen peroxide, tert -butanol, hydrochloric acid, sulfuric acid, humic acid, and ammonia (Voigt et al., 2024 ). Products were structurally elucidated by high-performance liquid chromatography combined with high-resolution hybrid-orbitrap mass spectrometry (HPLC-HRMS). Products with m/z = 276.1985 (V276), m/z = 264.1958 (n-desmethylvenlafaxine), m/z = 196.1333 (V196) and m/z = 194.1176 (V194) could be observed at 1.5 V (Voigt et al., 2024 ). Degradation kinetic monitoring as well as dwell time adjustment until complete degradation could be achieved in the batch reactor. To study product-formation at different voltages, the use of a flow cell is advantageous, since a substance can be continuously degraded at a certain flow rate. Its small volumes allow frequent contact with the electrode surface and hence rapid product formation, as compared to the synthesis cell used in the previous study. Simultaneously, mass voltammograms can be recorded to correlate product formation with voltages, whereas only a single voltage at a time can be applied in a batch reactor. The current study will investigate the product formation of venlafaxine and its metabolite o-desmethylvenlafaxine depending on the voltage. To this purpose, a flow cell is used. Focus is laid on the identification of oxidation products and on their preferred formation conditions. The voltage and thus the input of energy into the system is particularly interesting. Further, reaction pathways and mechanisms of the electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine shall be elucidated. The experimental setup used in this study with the expected mechanisms is shown in Fig. 1 . A QSAR analysis will be used to reveal potential risks to the environment. Finally, the suitability of electrochemical oxidation as a potential purification stage for eliminating the two substances is discussed. Methods Chemicals and reagents Venlafaxine hydrochloride ( > = 97.5%) and tert -butanol (99.5%) were purchased from Thermo Fisher Scientific (Geel, Belgium), o-Desmethylvenlafaxine from Dr. Ehrenstorfer (Wesel, Germany). For adjusting the pH of the solutions of venlafaxine, formic acid (Fluka-Honeywell, Seelze, Germany), sulfuric acid (96%, Bernd Kraft GmbH, Duisburg, Germany) and ammonia (approximately 25% Riedel-de Haen; pro analysis, Reag ISO, Reag Ph. Eur.) were used. Hydrogen peroxide was used as a 30% stabilized H 2 O 2 solution (Carl Roth, Karlsruhe, Germany). For the flow cell experiments, solutions containing either 20 ± 2 mg/L venlafaxine or 20 ± 6 mg/L o-desmethylvenlafaxine were prepared with ultrapure water (Berrytec, Grünwald, Germany). Both compounds yielded pH 6–7 after dissolution. For adjusting the pH to 8–9, ammonia was used. For the adjustment to pH 3–4, formic acid was used. For the comparison with sulfuric acid, the pH was acidified by sulfuric acid only. Electrochemical oxidation experiments Electrochemical oxidation experiments were carried out in a ROXY™ system (Antec Scientific, Zoeterwoude, The Netherlands), which consisted of an electrochemical flow cell (µPrepCell, Antec Scientific, Zoeterwoude, The Netherlands) and a potentiostat (Antec Scientific, Zoeterwoude, The Netherlands). The system was controlled with the Dialogue Elite™ software (Antec Scientific, Zoeterwoude, The Netherlands) version 2.21.8.1. The oven temperature was set to 35°C. The polarity was selected positive. A BDD working electrode with a boron level of 6000 to 8000 ppm was used for electrochemical oxidation. The ROXY™ system was connected to a high-resolution orbital ion trap hybrid mass spectrometer (Orbitrap IDX, ThermoFisher Scientific, Waltham, USA). The solutions were flowed through the electrochemical flow cell at a velocity of 50 µL/min. Mass spectra were recorded at a cell scan rate of 5 mV/s from 0 mV to 3500 mV. Mass voltammograms were recorded as the average of 15 scans and normalized by calculating a mean value from 0 to 500 mV for use as the initial value. After analysis of the recorded voltammograms, the ROXY™ system was disconnected from the mass spectrometer and samples were passed through the flow cell in a vial at constant voltage depending of the product formation voltage. These samples were analyzed using the HPLC-HRMS method described below for structure elucidation of the occurring oxidation products. HPLC-HRMS analysis Samples were transferred instantaneously for analysis to an ultra-high-performance liquid chromatography instrument (Vanquish Core, ThermoFisher Scientific, Waltham, USA) coupled to the electro spray ionization-quadrupole-ion trap-orbitrap (Orbitrap IDX, ThermoFisher Scientific, Waltham, USA). The injection volume was 5 µL. Reversed-phase chromatographic analysis was performed using an Eclipse Plus C18 (ZORBAX, 3.5 µm, 2.1x150 mm, Agilent, Waldbronn, Germany). During 10 minutes, the chromatography was performed at a flow rate of 0.3 mL min − 1 at a column temperature of 40°C. Eluents were ultrapure water as A and acetonitrile as B both acidified with 0.1% formic acid. Separation was performed isocratically with 80% eluent A and 20% eluent B. The observable mass range was set from 100 to 2000 m/z with a resolution set to 60000. With collision energy of 30 eV for MS 2 , a resolution of 30000, and 45 eV for MS 3 and a resolution of 60000, fragmentation was performed in the higher-energy collision-induced dissociation (HCD) cell. The spray voltage was set to 3500 V, the vaporizer and ion transfer tube temperature was 300°C. Instruments were controlled with Thermo Scientific XCalibur Version 4.3.73.11. For structure elucidation, accurate mass and isotope pattern were recorded allowing to derive the molecular formula. Tentative structures were generated using the software ACD/ChemSketch 2016.1.1 (ACDLabs, Toronto, ON, Canada) or MarvinSketch 17.28.0 (Chemaxon, Budapest, Hungary). Based on the initial chemical structure, plausible structures were identified. As next step, MS/MS and MS 3 spectra were inspected. Observed m/z values and differences were compared with expectancy values of fragments created from the plausible structures according to the standard fragmentation rules (Niessen, 2011 ; Niessen and Honing, 2015 ; Schymanski et al., 2015 ). Best matches with respect to fragmentation pathway and m/z values were considered as structurally confirmed. QSAR-Analysis For in silico ecotoxicity assessment QSAR analysis were performed using the software QSAR Toolbox Version 4.4.1. (LMC Oasis, Pourgas, Bulgaria). With the software ACD/ChemSketch 2016.1.1 (ACDLabs, Toronto, ON, Canada) or MarvinSketch 17.28.0 (Chemaxon, Budapest, Hungary chemical structures were drawn and loaded into the QSAR toolbox. ECOSAR (Ecological Structure-Activity Relationship), which were usual used for ecotoxicity analysis is implemented in the QSAR Toolbox and the class Aliphatic Amines 1.0. (median lethal concentration LC 50 and half maximal effective concentration (EC 50 )) were chosen. Acute and chronic toxicity (ChV) were thus predicted for the aquatic organism branchiopoda, actinopterygii and green algae. Venlafaxine, o-desmethylvenlafaxine and transformation products observed and identified were ranked from ecotoxic to non-ecotoxic. Results and discussion Electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine At first, the formation of oxidation products was structurally and quantitatively investigated. The pH values were varied between 3 and 9, which would represent the extreme limits for effluents, in order to find out an optimal pH range for effective electrochemical oxidation. The observed oxidation products are shown in Table 1 . Some of the observed oxidation products of venlafaxine were previously reported, when a synthesis cell was used (Voigt et al., 2024 ). Other products with smaller masses were detected using GC-MS analysis (Zhu et al., 2022 ). Further products were detected when using different electrodes like graphite screen printed electrode, SnO 2 /graphene-like carbon/TiO 2 or a carbon paste electrode modified with molecularly imprinted polymer‑coated magnetite nanoparticles. Corresponding molecular structures were proposed but not confirmed through analytical methods (Beitollahi et al., 2019 ; Kaur et al., 2021 ; Madrakian et al., 2016 ). In the current study, the product, V196a, was detected as higher voltage was applied than in our previous study. While all other products reached maximum signal intensity and hence their maximum concentration – due to structural similarity comparable ionization energies were assumed – at approximately 1.5 V, V196a was observed at 2 V. The product V276 was formed at pH 6 and 9, n-desmethylvenlafaxine only at pH 9. Acidic medium proved favorable for the formation of V196a. V196b and V194 were formed independent of the experimental conditions. For o-desmethylvenlafaxine, the electrochemical oxidation using BDD electrodes produced four new products O294, O278, O262 and O196, that could be structurally identified. O294 was only observed in the presence of formic acid. In neutral and alkaline medium, no oxidation products were observed, which was traced back to the low conductivity of the solution and thus the absence of electrochemical oxidation. The product O196 appeared to be identical to V196a as a result of the HPLC-HRMS and MS n analysis. Both products had the same retention times (data not shown) and equal fragmentation pathway in MS n experiments, cf. Table 1 . Most of the degradation products of venlafaxine and o-desmethylvenlafaxine were observed in an acidic environment. This can be exemplarily recognized from inspection of the mass voltammograms of venlafaxine and its product V196b at different pH values, cf. Figure 2 . Venlafaxine was disintegrated most in neutral medium at 3.5 V, followed by alkaline medium, and most poorly in acidic medium, which could not be explained as a consequence of product formation. The product V196b reached its highest concentration at approximately 1.5 V. It is formed particularly strongly in the acidic medium, followed by the neutral medium and least in the basic medium. This finding deviated hence from the observation for venlafaxine. While the formation of the intermediate V196b culminated at 1.5 V due to the biphasic build-up and degradation reactions, its degradation became more important due to the increase in hydroxyl radicals at further voltage increase. For the initial compound venlafaxine, the biphasic behavior did not occur due to the absence of the build-up phase. Product formation in acidic medium was due to the cleavage of the cyclohexanol ring. Adjusting the pH to 9 by adding ammonium led to an inhibition of the degradation of venlafaxine and the formation of V196b. This effect was traced back to the preferred electrochemical oxidation of ammonium, which does not induce the formation of radicals or reactive species that would further attack venlafaxine. As a consequence, the degradation of venlafaxine and the formation of V196b were suppressed. At this stage, the optimal pH value for electrochemical degradation cannot be identified. For o-desmethylvenlafaxine, electrochemical oxidation could only be observed at pH 3; for venlafaxine itself all three pH values may work while acidic medium proved favorable for a strong product formation. For an efficient destruction of the initial substance, the neutral range was favorable for venlafaxine, which would correspond to the pH range of natural waters. When no product formation is desired, the alkaline range would be most suitable. In the following, the mass voltammograms recorded for each experiment were examined in more detail and correlations between voltages and product formation were analyzed. Figure 3 shows exemplary the mass voltammograms for venlafaxine and o-desmethylvenlafaxine and the possible reaction pathways as a function of the voltage. The mass voltammograms reflect the course of transformation product formation depending on voltage increased with time. Voltages higher than 1.23 V cause EOTR leading to hydroxyl radical formation, cf. Eq. 2 (Kapałka et al., 2007 ). Since radical generation is intensified with voltage, increasing voltage led to increased product formation until a maximum for a given product was reached. After the maximum, the concentration of the product decreased again due to the formation of competition products and/or further transformation, as indicated in the scheme in Fig. 3 . This can be seen in the course of V196b. At approximately 1.4 V, V196b reached a maximum, while V194 started to form. Due to overlapping curves, the sequences of n-desmethylvenlafaxine, V196a and V278 could not be assigned unequivocally. Analogously for the oxidation products of o-desmethylvenlafaxine, the signals of O278, O294 and O262 overlapped with their maxima almost at the same level, hence no clear distinction was made. Yet, the product O196 was formed at higher voltages, and may have resulted from all the products formed at lower voltages. From transformation product structures and signal intensities, indices with respect to the formation mechanism could be derived. In the case of venlafaxine, the products V196b and V196a and in the case of o-desmethylvenlafaxine, the products O278, O294 and O196 were formed by hydroxyl radical reaction, which represents the indirect mechanism. As venlafaxine and o-desmethylvenlafaxine both possess a cyclohexanol moiety, its elimination occurred induced by hydroxyl substitution, albeit at different voltages for both compounds. Occasionally, a methyl group was also eliminated as in the case of the product of n-desmethylvenlafaxine, which itself was derived from venlafaxine. As a second major transformation, hydrogen elimination occurred, as can be seen exemplarily in the products V276 and O262. These products stemmed from electron transfer and thus from the direct electrochemical oxidation mechanism (Kapałka et al., 2007 ). In general, products became smaller, recognized by lower m/z ratios, with increasing voltage., cf. Figure 3 . The products V196a, V194 and O196 were still intensely present above 2.5 V. In conclusion, the higher the voltage, the stronger the destruction of venlafaxine and its metabolites. Influence of sulfuric acid and tert-butanol The addition of sulfuric acid and tert -butanol was expected to affect the oxidation of venlafaxine and o-venlafaxine via sulfate radicals and the trapping of hydroxyl radicals, such that the indirect pathway may be disrupted. The influence of sulfuric acid is demonstrated in the mass voltammograms of o-desmethylvenlafaxine and venlafaxine as compared to formic acid for pH adjustment, cf. Figure 4 . The comparison between the two mass voltammograms showed that the decomposition of venlafaxine and o-desmethylvenlafaxine were more efficient when sulfuric acid was used. The venlafaxine residue levels amounted to 33% in case of formic acid and 27% in case of sulfuric acid. The product concentrations were also diminished. For o-desmethylvenlafaxine, degradation proceeded similarly in the presence of both acids up to 2.5 V. At higher voltages, further degradation took place with sulfuric acid and did not reach a plateau above 3.5 V. At 3.5 V, 31% and 22% of o-desmethylvenlafaxine were still present with formic and sulfuric acid, respectively. The product formation yielded lower concentrations with sulfuric acid than with formic acid analogously to venlafaxine. The findings could be explained in terms of the sulfuric acid mechanisms, cf. Figure 1 . Sulfate radicals were formed, which contributed to the more effective degradation of venlafaxine. Yet, no sulfate containing transformation products could be observed, thus lacking the direct proof. Furthermore, no distinction could be made between the primary sulfate radical mechanism by direct electron transfer and the sulfate as secondary radical. The product O294 was no longer observed in the presence of sulfuric acid in comparison to formic acid, which might suggest a reduction of hydroxyl radicals in favor of sulfate radicals. Subsequently, the influence of tert -butanol was analyzed. Figure 5 shows the mass voltammograms of venlafaxine, o-desmethylvenlafaxine, V196b and O278. The transformation products of both venlafaxine and o-desmethylvenlafaxine showed noticeable changes in the mass voltammograms when tert -butanol was added. The higher the concentration of tert -butanol, the less the signal intensity of venlafaxine and o-desmethylvenlafaxine appeared in the mass spectrum, showing a plateau at higher voltages. A similar behavior was observed for venlafaxine at pH 6 and 9. In other words, electrochemical oxidation was less efficient in the presence of the radical scavenger. This observation was taken indicative for the predominance of the hydroxyl radical, thus the indirect mechanism. The finding was also evident in the product formation. The more tert -butanol was used, the lower the transformation product formation. This was true for all products of venlafaxine and o-desmethylvenlafaxine. By using radical scavengers, the hydroxyl radicals formed from water could diminished, which hampered or suppressed the indirect mechanism. In summary, the addition of sulfuric acid and tert-butanol did not give rise to transformation products that would suggest the intermediate occurrence of tert-butyl adducts or sulfate radicals according to equations 5 to 8. Yet, it increased or decreased the degradation efficiency of drug and oxidation products. From the finding, the hydroxyl or indirect mechanism according to equations 3 and 4 could be identified as the major pathway. In silico QSAR-Analysis For ecotoxicity assessment a QSAR analysis was performed. All results of QSAR analysis are summarized in Fig. 6 . The ranking was based on the predicted acute (LC 50 and EC 50 ) and chronic ecotoxicity (ChV) values of branchiopoda, actinopterygii and green algae. For n-desmethylvenlafaxine, a prediction could not be obtained due to the lack of sufficient data. Among the initial compounds and the proposed transformation products, venlafaxine was assigned with the highest ecotoxicity and V276 with slightly less toxicity. The product was formed at pH 6 and 9, which in consequence give preference to electrochemical degradation at pH 3 for venlafaxine from the ecotoxicological perspective. Smaller transformation products tended to be assigned with lower ecotoxicological risks. In the row of o-desmethylvenlafaxine, the oxidation product O262 was classified as more ecotoxic, while all other oxidation products were predicted less ecotoxic. In general, it can be observed that the predicted ecotoxicity decreased with decreasing molecular weight and with increasing number of hydroxyl groups. As a consequence, the indirect degradation mechanism produced less ecotoxic products than the direct electrochemical oxidation. Conclusion In this study, the electrochemical oxidation of venlafaxine and its metabolite o-desmethylvenlafaxine was investigated in a flow cell at different conditions, pH variation, addition of tert -butanol as a radical scavenger, and sulfuric acid as oxidant. Venlafaxine was oxidized at pH 3, 6 and 9 whereas o-desmethylvenlafaxine only at pH 3. In the case of venlafaxine, a total of five oxidation products was observed and structurally confirmed. In the case of o-desmethylvenlafaxine, four transformation products were newly elucidated. Through mass voltammograms, conditions and voltages for effective elimination of both initial compounds were studied. The addition of formic acid or ammonia had a negative impact on the destruction of venlafaxine. Sulfuric acid and pH adjustment to 3 improved degradation. Mechanistic studies using the radical scavenger tert -butanol suggested that hydroxyl radicals were the dominant oxidative pathway. With respect to a potential application of electrochemical oxidation as an advanced purification stage in WWTPs against venlafaxine and its metabolites, an ecotoxicological assessment based on the identified transformation product structures was conducted using in silico QSAR analysis. In general, the ecotoxicity was found to decrease when using electrochemical oxidation. Yet, this evaluation still needs to be confirmed by in vivo and/or in vitro ecotoxicity studies. List of abbreviations AOPs advanced oxidation processes BDD boron doped diamond ChV chronic toxicity EAOPs electrochemical advanced oxidation processes EC 50 half maximal effective concentration EU European union HCD higher-energy collision-induced dissociation HPLC high-performance liquid chromatography HRMS high-resolution hybrid-orbitrap mass spectrometry LC 50 median lethal concentration QSAR quantitative structure-activity relationships USA United States of America UV ultra violet WWTPs wastewater treatment plants Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Availability of data and material Data can be obtained upon request from the corresponding author. Competing interests The authors declare that they have no competing interests Funding Open Access funding enabled and organized by Project DEAL. We acknowledge support for the publication costs by the Open Access Publication Fund of Niederrhein University of Applied Sciences. Authors' contributions MV: conceptualization , validation , data curation, experiments , writing - original draft J-MD, NW, VL: data curation , preparation, experiments MJ: formal analysis , writing - review and editing, supervision References Beitollahi, H., Jahani, S., Tajik, S., Ganjali, M.R., Faridbod, F., Alizadeh, T., 2019. Voltammetric determination of venlafaxine as an antidepressant drug employing Gd2O3 nanoparticles graphite screen printed electrode. J. Rare Earths 37, 322–328. https://doi.org/10.1016/j.jre.2018.09.001 Bessegato, G.G., Zanoni, M.V.B., Tremiliosi-Filho, G., Lindino, C.A., 2019. Evidences of the Electrochemical Production of Sulfate Radicals at Cathodically Polarized TiO2 Nanotubes Electrodes. Electrocatalysis 10, 272–276. https://doi.org/10.1007/s12678-019-00525-6 Bisesi, J.H., Bridges, W., Klaine, S.J., 2014. 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The OH radical-induced chain reactions of methanol with hydrogen peroxide and with peroxodisulfate. J. Chem. Soc. Perkin Trans. 2 165–168. https://doi.org/10.1039/a808543i Voigt, M., Dluziak, J.-M., Wellen, N., Langerbein, V., Jaeger, M., 2024. Comparison of photoinduced and electrochemically induced degradation of venlafaxine. Environ. Sci. Pollut. Res. https://doi.org/10.1007/s11356-024-32018-5 Voigt, M., Jaeger, M., 2024. Efficiency increased advanced oxidation processes by persalts for the elimination of pharmaceuticals in waterbodies: a short review. Discov. Chem. Eng. 4, 16. https://doi.org/10.1007/s43938-024-00052-x Voigt, M., Jaeger, M., 2023. In silico and in vivo ecotoxicity—QSAR-based predictions and experimental assays for the aquatic environment, in: Hong, H.B.T.-Q. in S.E. and R.A. (Ed.), QSAR in Safety Evaluation and Risk Assessment. Elsevier, pp. 495–509. https://doi.org/10.1016/B978-0-443-15339-6.00018-7 Voigt, M., Wirtz, A., Hoffmann-Jacobsen, K., Jaeger, M., 2020. Prior art for the development of a fourth purification stage in wastewater treatment plant for the elimination of anthropogenic micropollutants-a short-review. AIMS Environ. Sci. 7, 69–98. https://doi.org/10.3934/environsci.2020005 Wang, J., Wang, S., 2021. Toxicity changes of wastewater during various advanced oxidation processes treatment: An overview. J. Clean. Prod. 315, 128202. https://doi.org/10.1016/j.jclepro.2021.128202 Wang, J., Zhuan, R., 2020. Degradation of antibiotics by advanced oxidation processes: An overview. Sci. Total Environ. 701, 135023. https://doi.org/10.1016/j.scitotenv.2019.135023 Wang, Z., Liu, M., Xiao, F., Postole, G., Zhao, H., Zhao, G., 2022. Recent advances and trends of heterogeneous electro-Fenton process for wastewater treatment-review. Chinese Chem. Lett. https://doi.org/10.1016/j.cclet.2021.07.044 Yu, B., Han, Q., Li, C., Zhu, Y., Jin, X., Dai, Z., 2022. Influencing factors of venlafaxine degradation at boron-doped diamond anode. Arab. J. Chem. 15, 103463. https://doi.org/10.1016/j.arabjc.2021.103463 Zhu, Y., Chang, B., Sun, X., Luo, H., Wang, W., Li, C., 2022. Chloride-mediated electrochemical degradation of the venlafaxine antidepressant. Environ. Technol. Innov. 25, 102189. https://doi.org/10.1016/j.eti.2021.102189 Table 1 Table 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.jpg Graphical abstract Table1.docx Cite Share Download PDF Status: Published Journal Publication published 10 Jul, 2025 Read the published version in Environmental Sciences Europe → Version 1 posted Editorial decision: Revision requested 19 May, 2025 Reviews received at journal 12 May, 2025 Reviews received at journal 06 May, 2025 Reviewers agreed at journal 29 Apr, 2025 Reviews received at journal 28 Apr, 2025 Reviewers agreed at journal 28 Apr, 2025 Reviewers agreed at journal 28 Apr, 2025 Reviewers invited by journal 27 Apr, 2025 Submission checks completed at journal 17 Apr, 2025 First submitted to journal 16 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6079652","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":449745345,"identity":"817a4fdd-f63d-4830-bb6c-0cd427f4a56f","order_by":0,"name":"Melanie Voigt","email":"","orcid":"","institution":"Niederrhein University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Melanie","middleName":"","lastName":"Voigt","suffix":""},{"id":449745346,"identity":"bf00f947-1ee7-405d-bb3b-a1bac846f2ee","order_by":1,"name":"Jean-Michel Dluziak","email":"","orcid":"","institution":"Niederrhein University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Jean-Michel","middleName":"","lastName":"Dluziak","suffix":""},{"id":449745347,"identity":"6bdb79e5-af41-456f-b428-de84c28e1702","order_by":2,"name":"Nils Wellen","email":"","orcid":"","institution":"Niederrhein University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Nils","middleName":"","lastName":"Wellen","suffix":""},{"id":449745348,"identity":"95f4ddcb-3386-4fae-bedd-4ce0bb56952b","order_by":3,"name":"Victoria Langerbein","email":"","orcid":"","institution":"Niederrhein University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Victoria","middleName":"","lastName":"Langerbein","suffix":""},{"id":449745349,"identity":"fbed0ba8-5518-48d0-a562-e8f92c5d13b7","order_by":4,"name":"Martin 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ammonia.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/0f78b88cc70fa6411bf730b7.jpg"},{"id":81674551,"identity":"e6e749c7-48ac-46e3-839d-3e43dbd34f4e","added_by":"auto","created_at":"2025-04-30 07:05:55","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":40855,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eNormalized mass voltammogram of a) venlafaxine and b) the product V196b at pH 3 adjusted with formic acid (red), pH 6 (green) and pH 9 adjusted with ammonia (blue).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/0ed6a84f6d0e82b568b1e436.jpg"},{"id":81674555,"identity":"76d8b1a6-4ba1-487b-9dfb-8a83490370c7","added_by":"auto","created_at":"2025-04-30 07:05:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":165071,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMass voltammograms of venlafaxine at a) pH 3 and b) pH 9 and of c) o-desmethylvenlafaxine at pH 3 acidified with H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eSO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and d) at pH 3 acidified with formic acid and addition of 10% \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003etert\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-butanol. Reaction pathways of electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine. Colors of mass voltammogram curves correspond with the colors of product names.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/a7acb0aeb1c4c99c4e68af55.jpg"},{"id":81674565,"identity":"6bcf26af-f4ff-4128-8fcb-2a558ee8e144","added_by":"auto","created_at":"2025-04-30 07:05:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":56753,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVoltammograms of a) venlafaxine (black), its transformation products V196b (blue), V194 (green), and V196a (orange) and of b) o-desmethylvenlafaxine (black) and its transformation products O278 (blue), O262 (orange), and O196 (green).\u003c/strong\u003e \u003cstrong\u003eDashed lines (- - -) correspond to the voltammograms taken in the presence of formic acid; the darker colors in the presence of sulfuric acid.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/46dd8dd8882af7aa0ce78210.jpg"},{"id":81674569,"identity":"04252ead-b8b0-4cff-b475-5d59a60d4686","added_by":"auto","created_at":"2025-04-30 07:05:56","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":72810,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMass voltammograms of a) venlafaxine, b) o-desmethylvenlafaxine, c) V196 and d) O278 in the absence of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003etert\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-butanol (red), in the presence of 10% \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003etert\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-butanol (orange) and of 30% \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003etert\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-butanol (yellow)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/9fec7008bdeeac5447246161.jpg"},{"id":81674553,"identity":"dd8e171d-6d5a-47bf-88f3-fc4baa46e982","added_by":"auto","created_at":"2025-04-30 07:05:56","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":70858,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eQSAR Analysis of venlafaxine and o-desmethylvenlafaxine and their transformation products\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/1f9d96dc7a4cd267debe5ab5.jpg"},{"id":86699438,"identity":"d69ca7ee-bb4e-48d7-b6e2-89146f5b88e3","added_by":"auto","created_at":"2025-07-14 16:09:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1798621,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/7bbbed9d-688f-407f-9575-01cc4958d171.pdf"},{"id":81674549,"identity":"e67f3027-654e-4e7e-8f05-2f40bab8a7b5","added_by":"auto","created_at":"2025-04-30 07:05:55","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":53203,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"Graphicalabstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/d069786c388289bb4e5bed85.jpg"},{"id":81675169,"identity":"19bae7e0-59e1-4212-9694-9cd6189d5ab6","added_by":"auto","created_at":"2025-04-30 07:13:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":86914,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6079652/v1/72ef83d4cf6484aa4fe1043d.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Monitoring of the electrochemical oxidation of venlafaxine and its metabolite o- desmethylvenlafaxine using a flow cell and high-resolution mass spectrometry","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eFive products were detected by HRMS during the electrochemical oxidation of venlafaxine.\u003c/li\u003e\n \u003cli\u003eFour new products were identified during the electrochemical oxidation of o-desmethylvenlafaxine by HRMS analysis.\u003c/li\u003e\n \u003cli\u003eThe indirect mechanism dominates the electrochemical oxidation.\u003c/li\u003e\n \u003cli\u003eThe addition of sulfuric acid favors the electrochemical oxidation only slightly.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003e\u003cem\u003eIn silico\u003c/em\u003e ecotoxicity assessment showed that most transformation products were less toxic than the initial drug substance.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Background","content":"\u003cp\u003eVenlafaxine is used as an antidepressant medicine. It is applied as a prodrug of its main active metabolite o-desmethylvenlafaxine (Dean, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Eh-Haj, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Due to its frequent prescription, venlafaxine and its metabolites n-desmethylvenlafaxine, o-desmethylvenlafaxine n,n-didesmethylvenlafaxine and n,o-didesmethylvenlafaxine are regularly detected in various waters at concentrations up to 590 \u0026micro;g/L (Dusi et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In surface water, venlafaxine was observed at 400 \u0026micro;g/L in Argentina and at 2.61 \u0026micro;g/L in the United States (Dusi et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Like many pharmaceuticals, venlafaxine and its metabolites cannot be completely eliminated from wastewater through the three common purification stages of conventional waste water treatment plants (WWTPs), i.e. the mechanical, biological and chemical stages and were regular found in effluents (Dusi et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kilpinen et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kosma et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Lin et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Hence WWTPs act as the main entry routes of many pharmaceuticals. Since sufficient data on the prevalence of some substances in the aquatic environment are not available, the European Union introduced a watchlist of substances to be monitored across the European Union in the field of water policy according to Article 8b of the Directive 2008/105/EC (European Commission, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) in 2015. The list is updated every few years. The substances venlafaxine and o-desmethylvenlafaxine investigated in this study appeared on the third and remain on the current fourth EU watchlist (European Commission, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eVenlafaxine has a negative effect on the aquatic environment. It has already been shown to affect the gene expression of salmon, as well as reducing the serotonin concentration in the brain of hybrid striped bass and impairing their hunting behavior (Bisesi et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Hodkovicova et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). It can also lead to the isolation of the feet of freshwater snails, conches and other mollusks (Fong and Molnar, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In order to minimize a potential threat to the aquatic environment and to eliminate pharmaceuticals from WWTP effluents, research has been conducted on various advanced processes for several years to extend the conventional purification stages. These include advanced oxidation processes (AOPs), such as the use of ozone or UV irradiation (Coha et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Voigt et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Wang and Wang, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Common feature of AOPs is the formation and chemistry of hydroxyl radicals (HO\u003csup\u003e\u0026bull;\u003c/sup\u003e). Hence electrochemical oxidation belongs to the AOPs. Due to their high standard oxidation\u0026ndash;reduction potential of 2.8V, HO\u003csup\u003e\u0026bull;\u003c/sup\u003e are often able to mineralize organic substances such as pharmaceuticals and other anthropogenic micropollutants (Chaplin, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Moreira et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Various electrodes, such as boron-doped diamond (BDD), glassy carbon, titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) and lead dioxide (PbO\u003csub\u003e2\u003c/sub\u003e), are being investigated for their suitability for electrochemical oxidation processes (Wang and Zhuan, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The BDD electrodes proved particularly efficient and were found the most non-active anode suitable for anodic oxidation (Chaplin, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Lozano et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; McBeath et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Moreira et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Micropollutants R are oxidized directly by electron transfer to the BDD electrode, cf. Eq.\u0026nbsp;1, with the stoichiometric coefficients x and y (Moradi et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). An electrochemical oxidation transfer reaction (EOTR) occurs at voltages higher than 1.23 V (Kapałka et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Here, hydroxyl radicals are generated from water discharge at the anodic active side of the BDD electrode, see Eq.\u0026nbsp;2. The hydroxyl radicals oxidize and eventually mineralize the micropollutants completely, cf. Eq.\u0026nbsp;3, The mineralization reaction competes with the anodic discharge of the hydroxyl radicals to molecular oxygen, cf. Eq.\u0026nbsp;4.\u003c/p\u003e \u003cp\u003eR\u0026thinsp;+\u0026thinsp;x(e\u003csup\u003e\u0026minus;\u003c/sup\u003e)BDD \u0026rarr; xBDD\u0026thinsp;+\u0026thinsp;Mineralization products\u0026thinsp;+\u0026thinsp;yH\u003csup\u003e+\u003c/sup\u003e + ye\u003csup\u003e\u0026minus;\u003c/sup\u003e (1)\u003c/p\u003e \u003cp\u003eBDD\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; BDD(.OH)\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e (2)\u003c/p\u003e \u003cp\u003eR\u0026thinsp;+\u0026thinsp;x(.OH)BDD \u0026rarr; xBDD\u0026thinsp;+\u0026thinsp;Mineralization products\u0026thinsp;+\u0026thinsp;yH\u003csup\u003e+\u003c/sup\u003e + ye\u003csup\u003e\u0026minus;\u003c/sup\u003e (3)\u003c/p\u003e \u003cp\u003eBDD(.OH) \u0026rarr; BDD + \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{1}{2}\\)\u003c/span\u003e\u003c/span\u003e O\u003csub\u003e2\u003c/sub\u003e + H\u003csup\u003e+\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e (4)\u003c/p\u003e \u003cp\u003eAdditives such as sulfuric acid or hydrochloric acid can further promote degradation (Sir\u0026eacute;s et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). These acids increase the conductivity, change the pH and intensify the formation of reactive oxygen species, thus augmenting the degradation efficiency. Furthermore, persalts or Fenton reagents are well known for enhancing electrochemical oxidation (Voigt and Jaeger, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The degradation kinetics of venlafaxine were also investigated at different conditions, where an increase in current density was found to accelerate the degradation (Yu et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe addition of sulfuric acid, ammonia and \u003cem\u003etert\u003c/em\u003e-butanol may induce different oxidation mechanisms. Two main mechanisms have been reported in the absence of such additives: the direct pathway, where a substance is degraded directly by electron transfer and oxidation, and the indirect pathway where hydroxyl radicals are formed by electrochemical oxidation of water and the substance is oxidized through the radicals (Moreira et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Sir\u0026eacute;s et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Voigt et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Addition of sulfuric acid leads to two additional reaction mechanisms. On the major pathway, hydroxyl radicals generate sulfate radicals, see Eqs.\u0026nbsp;5 and 6 depending on the pH (Bessegato et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Davis et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The secondary sulfate radicals induce the elimination of the substance. The second sulfate pathway results in the direct formation of sulfate radicals at the BDD electrode, see equations 6 and 7, while the recombination of two sulfate radicals is possible leading to the peroxy species, cf. Eq.\u0026nbsp;8 (Farhat et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + .OH\u0026rarr;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{S}\\text{O}}_{4}^{\u0026middot;-}\\)\u003c/span\u003e\u003c/span\u003e+H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e (5)\u003c/p\u003e \u003cp\u003eHS\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{O}}_{4}^{-}\\)\u003c/span\u003e\u003c/span\u003e+ .OH\u0026rarr;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{S}\\text{O}}_{4}^{\u0026middot;-}\\)\u003c/span\u003e\u003c/span\u003e+H\u003csub\u003e2\u003c/sub\u003eO (6)\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{S}\\text{O}}_{4}^{2-}+\\text{B}\\text{D}\\text{D}\\:\\)\u003c/span\u003e \u003c/span\u003e\u0026rarr;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{B}\\text{D}\\text{D}(\\text{S}\\text{O}}_{4}^{\u0026middot;-})\\)\u003c/span\u003e\u003c/span\u003e+e\u003csup\u003e\u0026minus;\u003c/sup\u003e (7)\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{S}\\text{O}}_{4}^{\u0026middot;-}+{\\text{S}\\text{O}}_{4}^{\u0026middot;-}\\)\u003c/span\u003e \u003c/span\u003e\u0026rarr;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{S}}_{2}{\\text{O}}_{8}^{2-}\\)\u003c/span\u003e\u003c/span\u003e (8)\u003c/p\u003e \u003cp\u003eRadical scavengers, such as \u003cem\u003etert\u003c/em\u003e-butanol, capture the hydroxyl radicals and thus decelerate the electrochemical oxidation (Chen et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The mechanism is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Two \u003cem\u003etert\u003c/em\u003e-butanol molecules scavenge two hydroxyl radicals leading to the formation of water and, since the \u003cem\u003etert\u003c/em\u003e-butyl radicals are less reactive, to recombination (Ulanski and von Sonntag, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Recently, a mechanism leading to tert-butyl peroxyl radicals, when oxygen is present in solution, has been discussed, with the latter radicals being also less reactive (Gao et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For the addition of ammonia, several mechanisms for the BDD-electrochemical oxidation have been described, cf. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and equations 9 and 10 (Michels et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNH\u003csub\u003e3\u003c/sub\u003e\u0026rarr;.NH\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e+e\u003csup\u003e\u0026minus;\u003c/sup\u003e (9)\u003c/p\u003e \u003cp\u003e2NH\u003csub\u003e3\u003c/sub\u003e\u0026rarr;N\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;6H\u003csup\u003e+\u003c/sup\u003e+6e\u003csup\u003e\u0026minus;\u003c/sup\u003e (10)\u003c/p\u003e \u003cp\u003eThe different mechanisms cause different products with different ecotoxic potential. Since electrochemical oxidation reactions often yield a mixture of products, whose ecotoxicological hazard may prove difficult to assess \u003cem\u003ein vivo\u003c/em\u003e, \u003cem\u003ein silico\u003c/em\u003e methods, such as quantitative structure-activity relation (QSAR) analysis, are often used to predict the ecotoxicity of individual substances using mathematical models (Voigt and Jaeger, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn a preceding study, the BDD-electrochemical degradation of venlafaxine was investigated in a synthesis cell at a constant voltage of 1.5 V under various conditions, such as the addition of hydrogen peroxide, \u003cem\u003etert\u003c/em\u003e-butanol, hydrochloric acid, sulfuric acid, humic acid, and ammonia (Voigt et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Products were structurally elucidated by high-performance liquid chromatography combined with high-resolution hybrid-orbitrap mass spectrometry (HPLC-HRMS). Products with m/z\u0026thinsp;=\u0026thinsp;276.1985 (V276), m/z\u0026thinsp;=\u0026thinsp;264.1958 (n-desmethylvenlafaxine), m/z\u0026thinsp;=\u0026thinsp;196.1333 (V196) and m/z\u0026thinsp;=\u0026thinsp;194.1176 (V194) could be observed at 1.5 V (Voigt et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Degradation kinetic monitoring as well as dwell time adjustment until complete degradation could be achieved in the batch reactor. To study product-formation at different voltages, the use of a flow cell is advantageous, since a substance can be continuously degraded at a certain flow rate. Its small volumes allow frequent contact with the electrode surface and hence rapid product formation, as compared to the synthesis cell used in the previous study. Simultaneously, mass voltammograms can be recorded to correlate product formation with voltages, whereas only a single voltage at a time can be applied in a batch reactor.\u003c/p\u003e \u003cp\u003eThe current study will investigate the product formation of venlafaxine and its metabolite o-desmethylvenlafaxine depending on the voltage. To this purpose, a flow cell is used. Focus is laid on the identification of oxidation products and on their preferred formation conditions. The voltage and thus the input of energy into the system is particularly interesting. Further, reaction pathways and mechanisms of the electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine shall be elucidated. The experimental setup used in this study with the expected mechanisms is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A QSAR analysis will be used to reveal potential risks to the environment. Finally, the suitability of electrochemical oxidation as a potential purification stage for eliminating the two substances is discussed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eChemicals and reagents\u003c/h2\u003e \u003cp\u003eVenlafaxine hydrochloride (\u0026thinsp;\u0026gt;\u0026thinsp;=\u0026thinsp;97.5%) and \u003cem\u003etert\u003c/em\u003e-butanol (99.5%) were purchased from Thermo Fisher Scientific (Geel, Belgium), o-Desmethylvenlafaxine from Dr. Ehrenstorfer (Wesel, Germany). For adjusting the pH of the solutions of venlafaxine, formic acid (Fluka-Honeywell, Seelze, Germany), sulfuric acid (96%, Bernd Kraft GmbH, Duisburg, Germany) and ammonia (approximately 25% Riedel-de Haen; pro analysis, Reag ISO, Reag Ph. Eur.) were used. Hydrogen peroxide was used as a 30% stabilized H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution (Carl Roth, Karlsruhe, Germany). For the flow cell experiments, solutions containing either 20\u0026thinsp;\u0026plusmn;\u0026thinsp;2 mg/L venlafaxine or 20\u0026thinsp;\u0026plusmn;\u0026thinsp;6 mg/L o-desmethylvenlafaxine were prepared with ultrapure water (Berrytec, Gr\u0026uuml;nwald, Germany). Both compounds yielded pH 6\u0026ndash;7 after dissolution. For adjusting the pH to 8\u0026ndash;9, ammonia was used. For the adjustment to pH 3\u0026ndash;4, formic acid was used. For the comparison with sulfuric acid, the pH was acidified by sulfuric acid only.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrochemical oxidation experiments\u003c/h3\u003e\n\u003cp\u003eElectrochemical oxidation experiments were carried out in a ROXY\u0026trade; system (Antec Scientific, Zoeterwoude, The Netherlands), which consisted of an electrochemical flow cell (\u0026micro;PrepCell, Antec Scientific, Zoeterwoude, The Netherlands) and a potentiostat (Antec Scientific, Zoeterwoude, The Netherlands). The system was controlled with the Dialogue Elite\u0026trade; software (Antec Scientific, Zoeterwoude, The Netherlands) version 2.21.8.1. The oven temperature was set to 35\u0026deg;C. The polarity was selected positive. A BDD working electrode with a boron level of 6000 to 8000 ppm was used for electrochemical oxidation. The ROXY\u0026trade; system was connected to a high-resolution orbital ion trap hybrid mass spectrometer (Orbitrap IDX, ThermoFisher Scientific, Waltham, USA). The solutions were flowed through the electrochemical flow cell at a velocity of 50 \u0026micro;L/min. Mass spectra were recorded at a cell scan rate of 5 mV/s from 0 mV to 3500 mV. Mass voltammograms were recorded as the average of 15 scans and normalized by calculating a mean value from 0 to 500 mV for use as the initial value. After analysis of the recorded voltammograms, the ROXY\u0026trade; system was disconnected from the mass spectrometer and samples were passed through the flow cell in a vial at constant voltage depending of the product formation voltage. These samples were analyzed using the HPLC-HRMS method described below for structure elucidation of the occurring oxidation products.\u003c/p\u003e\n\u003ch3\u003eHPLC-HRMS analysis\u003c/h3\u003e\n\u003cp\u003eSamples were transferred instantaneously for analysis to an ultra-high-performance liquid chromatography instrument (Vanquish Core, ThermoFisher Scientific, Waltham, USA) coupled to the electro spray ionization-quadrupole-ion trap-orbitrap (Orbitrap IDX, ThermoFisher Scientific, Waltham, USA). The injection volume was 5 \u0026micro;L. Reversed-phase chromatographic analysis was performed using an Eclipse Plus C18 (ZORBAX, 3.5 \u0026micro;m, 2.1x150 mm, Agilent, Waldbronn, Germany). During 10 minutes, the chromatography was performed at a flow rate of 0.3 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a column temperature of 40\u0026deg;C. Eluents were ultrapure water as A and acetonitrile as B both acidified with 0.1% formic acid. Separation was performed isocratically with 80% eluent A and 20% eluent B. The observable mass range was set from 100 to 2000 \u003cem\u003em/z\u003c/em\u003e with a resolution set to 60000. With collision energy of 30 eV for MS\u003csup\u003e2\u003c/sup\u003e, a resolution of 30000, and 45 eV for MS\u003csup\u003e3\u003c/sup\u003e and a resolution of 60000, fragmentation was performed in the higher-energy collision-induced dissociation (HCD) cell. The spray voltage was set to 3500 V, the vaporizer and ion transfer tube temperature was 300\u0026deg;C. Instruments were controlled with Thermo Scientific XCalibur Version 4.3.73.11.\u003c/p\u003e \u003cp\u003eFor structure elucidation, accurate mass and isotope pattern were recorded allowing to derive the molecular formula. Tentative structures were generated using the software ACD/ChemSketch 2016.1.1 (ACDLabs, Toronto, ON, Canada) or MarvinSketch 17.28.0 (Chemaxon, Budapest, Hungary). Based on the initial chemical structure, plausible structures were identified. As next step, MS/MS and MS\u003csup\u003e3\u003c/sup\u003e spectra were inspected. Observed \u003cem\u003em/z\u003c/em\u003e values and differences were compared with expectancy values of fragments created from the plausible structures according to the standard fragmentation rules (Niessen, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Niessen and Honing, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Schymanski et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Best matches with respect to fragmentation pathway and \u003cem\u003em/z\u003c/em\u003e values were considered as structurally confirmed.\u003c/p\u003e\n\u003ch3\u003eQSAR-Analysis\u003c/h3\u003e\n\u003cp\u003eFor \u003cem\u003ein silico\u003c/em\u003e ecotoxicity assessment QSAR analysis were performed using the software QSAR Toolbox Version 4.4.1. (LMC Oasis, Pourgas, Bulgaria). With the software ACD/ChemSketch 2016.1.1 (ACDLabs, Toronto, ON, Canada) or MarvinSketch 17.28.0 (Chemaxon, Budapest, Hungary chemical structures were drawn and loaded into the QSAR toolbox. ECOSAR (Ecological Structure-Activity Relationship), which were usual used for ecotoxicity analysis is implemented in the QSAR Toolbox and the class Aliphatic Amines 1.0. (median lethal concentration LC\u003csub\u003e50\u003c/sub\u003e and half maximal effective concentration (EC\u003csub\u003e50\u003c/sub\u003e)) were chosen. Acute and chronic toxicity (ChV) were thus predicted for the aquatic organism branchiopoda, actinopterygii and green algae. Venlafaxine, o-desmethylvenlafaxine and transformation products observed and identified were ranked from ecotoxic to non-ecotoxic.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical oxidation of venlafaxine and o-desmethylvenlafaxine\u003c/h2\u003e \u003cp\u003eAt first, the formation of oxidation products was structurally and quantitatively investigated. The pH values were varied between 3 and 9, which would represent the extreme limits for effluents, in order to find out an optimal pH range for effective electrochemical oxidation. The observed oxidation products are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eSome of the observed oxidation products of venlafaxine were previously reported, when a synthesis cell was used (Voigt et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Other products with smaller masses were detected using GC-MS analysis (Zhu et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Further products were detected when using different electrodes like graphite screen printed electrode, SnO\u003csub\u003e2\u003c/sub\u003e/graphene-like carbon/TiO\u003csub\u003e2\u003c/sub\u003e or a carbon paste electrode modified with molecularly imprinted polymer‑coated magnetite nanoparticles. Corresponding molecular structures were proposed but not confirmed through analytical methods (Beitollahi et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kaur et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Madrakian et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In the current study, the product, V196a, was detected as higher voltage was applied than in our previous study. While all other products reached maximum signal intensity and hence their maximum concentration \u0026ndash; due to structural similarity comparable ionization energies were assumed \u0026ndash; at approximately 1.5 V, V196a was observed at 2 V. The product V276 was formed at pH 6 and 9, n-desmethylvenlafaxine only at pH 9. Acidic medium proved favorable for the formation of V196a. V196b and V194 were formed independent of the experimental conditions.\u003c/p\u003e \u003cp\u003eFor o-desmethylvenlafaxine, the electrochemical oxidation using BDD electrodes produced four new products O294, O278, O262 and O196, that could be structurally identified. O294 was only observed in the presence of formic acid. In neutral and alkaline medium, no oxidation products were observed, which was traced back to the low conductivity of the solution and thus the absence of electrochemical oxidation. The product O196 appeared to be identical to V196a as a result of the HPLC-HRMS and MS\u003csup\u003en\u003c/sup\u003e analysis. Both products had the same retention times (data not shown) and equal fragmentation pathway in MS\u003csup\u003en\u003c/sup\u003e experiments, cf. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eMost of the degradation products of venlafaxine and o-desmethylvenlafaxine were observed in an acidic environment. This can be exemplarily recognized from inspection of the mass voltammograms of venlafaxine and its product V196b at different pH values, cf. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eVenlafaxine was disintegrated most in neutral medium at 3.5 V, followed by alkaline medium, and most poorly in acidic medium, which could not be explained as a consequence of product formation. The product V196b reached its highest concentration at approximately 1.5 V. It is formed particularly strongly in the acidic medium, followed by the neutral medium and least in the basic medium. This finding deviated hence from the observation for venlafaxine. While the formation of the intermediate V196b culminated at 1.5 V due to the biphasic build-up and degradation reactions, its degradation became more important due to the increase in hydroxyl radicals at further voltage increase. For the initial compound venlafaxine, the biphasic behavior did not occur due to the absence of the build-up phase. Product formation in acidic medium was due to the cleavage of the cyclohexanol ring. Adjusting the pH to 9 by adding ammonium led to an inhibition of the degradation of venlafaxine and the formation of V196b. This effect was traced back to the preferred electrochemical oxidation of ammonium, which does not induce the formation of radicals or reactive species that would further attack venlafaxine. As a consequence, the degradation of venlafaxine and the formation of V196b were suppressed.\u003c/p\u003e \u003cp\u003eAt this stage, the optimal pH value for electrochemical degradation cannot be identified. For o-desmethylvenlafaxine, electrochemical oxidation could only be observed at pH 3; for venlafaxine itself all three pH values may work while acidic medium proved favorable for a strong product formation. For an efficient destruction of the initial substance, the neutral range was favorable for venlafaxine, which would correspond to the pH range of natural waters. When no product formation is desired, the alkaline range would be most suitable.\u003c/p\u003e \u003cp\u003eIn the following, the mass voltammograms recorded for each experiment were examined in more detail and correlations between voltages and product formation were analyzed. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows exemplary the mass voltammograms for venlafaxine and o-desmethylvenlafaxine and the possible reaction pathways as a function of the voltage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe mass voltammograms reflect the course of transformation product formation depending on voltage increased with time. Voltages higher than 1.23 V cause EOTR leading to hydroxyl radical formation, cf. Eq.\u0026nbsp;2 (Kapałka et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Since radical generation is intensified with voltage, increasing voltage led to increased product formation until a maximum for a given product was reached. After the maximum, the concentration of the product decreased again due to the formation of competition products and/or further transformation, as indicated in the scheme in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This can be seen in the course of V196b. At approximately 1.4 V, V196b reached a maximum, while V194 started to form. Due to overlapping curves, the sequences of n-desmethylvenlafaxine, V196a and V278 could not be assigned unequivocally. Analogously for the oxidation products of o-desmethylvenlafaxine, the signals of O278, O294 and O262 overlapped with their maxima almost at the same level, hence no clear distinction was made. Yet, the product O196 was formed at higher voltages, and may have resulted from all the products formed at lower voltages.\u003c/p\u003e \u003cp\u003eFrom transformation product structures and signal intensities, indices with respect to the formation mechanism could be derived. In the case of venlafaxine, the products V196b and V196a and in the case of o-desmethylvenlafaxine, the products O278, O294 and O196 were formed by hydroxyl radical reaction, which represents the indirect mechanism. As venlafaxine and o-desmethylvenlafaxine both possess a cyclohexanol moiety, its elimination occurred induced by hydroxyl substitution, albeit at different voltages for both compounds. Occasionally, a methyl group was also eliminated as in the case of the product of n-desmethylvenlafaxine, which itself was derived from venlafaxine. As a second major transformation, hydrogen elimination occurred, as can be seen exemplarily in the products V276 and O262. These products stemmed from electron transfer and thus from the direct electrochemical oxidation mechanism (Kapałka et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn general, products became smaller, recognized by lower m/z ratios, with increasing voltage., cf. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The products V196a, V194 and O196 were still intensely present above 2.5 V. In conclusion, the higher the voltage, the stronger the destruction of venlafaxine and its metabolites.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eInfluence of sulfuric acid and tert-butanol\u003c/h3\u003e\n\u003cp\u003eThe addition of sulfuric acid and \u003cem\u003etert\u003c/em\u003e-butanol was expected to affect the oxidation of venlafaxine and o-venlafaxine via sulfate radicals and the trapping of hydroxyl radicals, such that the indirect pathway may be disrupted. The influence of sulfuric acid is demonstrated in the mass voltammograms of o-desmethylvenlafaxine and venlafaxine as compared to formic acid for pH adjustment, cf. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe comparison between the two mass voltammograms showed that the decomposition of venlafaxine and o-desmethylvenlafaxine were more efficient when sulfuric acid was used. The venlafaxine residue levels amounted to 33% in case of formic acid and 27% in case of sulfuric acid. The product concentrations were also diminished. For o-desmethylvenlafaxine, degradation proceeded similarly in the presence of both acids up to 2.5 V. At higher voltages, further degradation took place with sulfuric acid and did not reach a plateau above 3.5 V. At 3.5 V, 31% and 22% of o-desmethylvenlafaxine were still present with formic and sulfuric acid, respectively. The product formation yielded lower concentrations with sulfuric acid than with formic acid analogously to venlafaxine. The findings could be explained in terms of the sulfuric acid mechanisms, cf. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Sulfate radicals were formed, which contributed to the more effective degradation of venlafaxine. Yet, no sulfate containing transformation products could be observed, thus lacking the direct proof. Furthermore, no distinction could be made between the primary sulfate radical mechanism by direct electron transfer and the sulfate as secondary radical. The product O294 was no longer observed in the presence of sulfuric acid in comparison to formic acid, which might suggest a reduction of hydroxyl radicals in favor of sulfate radicals. Subsequently, the influence of \u003cem\u003etert\u003c/em\u003e-butanol was analyzed. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the mass voltammograms of venlafaxine, o-desmethylvenlafaxine, V196b and O278.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe transformation products of both venlafaxine and o-desmethylvenlafaxine showed noticeable changes in the mass voltammograms when \u003cem\u003etert\u003c/em\u003e-butanol was added. The higher the concentration of \u003cem\u003etert\u003c/em\u003e-butanol, the less the signal intensity of venlafaxine and o-desmethylvenlafaxine appeared in the mass spectrum, showing a plateau at higher voltages. A similar behavior was observed for venlafaxine at pH 6 and 9. In other words, electrochemical oxidation was less efficient in the presence of the radical scavenger. This observation was taken indicative for the predominance of the hydroxyl radical, thus the indirect mechanism. The finding was also evident in the product formation. The more \u003cem\u003etert\u003c/em\u003e-butanol was used, the lower the transformation product formation. This was true for all products of venlafaxine and o-desmethylvenlafaxine. By using radical scavengers, the hydroxyl radicals formed from water could diminished, which hampered or suppressed the indirect mechanism. In summary, the addition of sulfuric acid and tert-butanol did not give rise to transformation products that would suggest the intermediate occurrence of tert-butyl adducts or sulfate radicals according to equations 5 to 8. Yet, it increased or decreased the degradation efficiency of drug and oxidation products. From the finding, the hydroxyl or indirect mechanism according to equations 3 and 4 could be identified as the major pathway.\u003c/p\u003e\n\u003ch3\u003eIn silico QSAR-Analysis\u003c/h3\u003e\n\u003cp\u003eFor ecotoxicity assessment a QSAR analysis was performed. All results of QSAR analysis are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The ranking was based on the predicted acute (LC\u003csub\u003e50\u003c/sub\u003e and EC\u003csub\u003e50\u003c/sub\u003e) and chronic ecotoxicity (ChV) values of branchiopoda, actinopterygii and green algae. For n-desmethylvenlafaxine, a prediction could not be obtained due to the lack of sufficient data.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong the initial compounds and the proposed transformation products, venlafaxine was assigned with the highest ecotoxicity and V276 with slightly less toxicity. The product was formed at pH 6 and 9, which in consequence give preference to electrochemical degradation at pH 3 for venlafaxine from the ecotoxicological perspective. Smaller transformation products tended to be assigned with lower ecotoxicological risks. In the row of o-desmethylvenlafaxine, the oxidation product O262 was classified as more ecotoxic, while all other oxidation products were predicted less ecotoxic.\u003c/p\u003e \u003cp\u003eIn general, it can be observed that the predicted ecotoxicity decreased with decreasing molecular weight and with increasing number of hydroxyl groups. As a consequence, the indirect degradation mechanism produced less ecotoxic products than the direct electrochemical oxidation.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, the electrochemical oxidation of venlafaxine and its metabolite o-desmethylvenlafaxine was investigated in a flow cell at different conditions, pH variation, addition of \u003cem\u003etert\u003c/em\u003e-butanol as a radical scavenger, and sulfuric acid as oxidant. Venlafaxine was oxidized at pH 3, 6 and 9 whereas o-desmethylvenlafaxine only at pH 3. In the case of venlafaxine, a total of five oxidation products was observed and structurally confirmed. In the case of o-desmethylvenlafaxine, four transformation products were newly elucidated. Through mass voltammograms, conditions and voltages for effective elimination of both initial compounds were studied. The addition of formic acid or ammonia had a negative impact on the destruction of venlafaxine. Sulfuric acid and pH adjustment to 3 improved degradation. Mechanistic studies using the radical scavenger \u003cem\u003etert\u003c/em\u003e-butanol suggested that hydroxyl radicals were the dominant oxidative pathway. With respect to a potential application of electrochemical oxidation as an advanced purification stage in WWTPs against venlafaxine and its metabolites, an ecotoxicological assessment based on the identified transformation product structures was conducted using \u003cem\u003ein silico\u003c/em\u003e QSAR analysis. In general, the ecotoxicity was found to decrease when using electrochemical oxidation. Yet, this evaluation still needs to be confirmed by \u003cem\u003ein vivo\u003c/em\u003e and/or \u003cem\u003ein vitro\u003c/em\u003e ecotoxicity studies.\u003c/p\u003e"},{"header":"List of abbreviations","content":"\u003cp\u003eAOPs\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;advanced oxidation processes\u003c/p\u003e\n\u003cp\u003eBDD\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;boron doped diamond\u003c/p\u003e\n\u003cp\u003eChV\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;chronic toxicity\u003c/p\u003e\n\u003cp\u003eEAOPs\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;electrochemical advanced oxidation processes\u003c/p\u003e\n\u003cp\u003eEC\u003csub\u003e50\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;half maximal effective concentration\u003c/p\u003e\n\u003cp\u003eEU\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;European union\u003c/p\u003e\n\u003cp\u003eHCD\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;higher-energy collision-induced dissociation\u003c/p\u003e\n\u003cp\u003eHPLC\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;high-performance liquid chromatography\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHRMS\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;high-resolution hybrid-orbitrap mass spectrometry\u003c/p\u003e\n\u003cp\u003eLC\u003csub\u003e50\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;median lethal concentration\u003c/p\u003e\n\u003cp\u003eQSAR\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;quantitative structure-activity relationships\u003c/p\u003e\n\u003cp\u003eUSA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;United States of America\u003c/p\u003e\n\u003cp\u003eUV\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;ultra violet\u003c/p\u003e\n\u003cp\u003eWWTPs \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; wastewater treatment plants\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData can be obtained upon request from the corresponding author.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOpen Access funding enabled and organized by Project DEAL. We acknowledge support for the publication costs by the Open Access Publication Fund of Niederrhein University of Applied Sciences.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMV:\u0026nbsp;\u003c/strong\u003econceptualization\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003evalidation\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003edata curation, experiments\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003ewriting\u003cstrong\u003e\u0026nbsp;-\u0026nbsp;\u003c/strong\u003eoriginal draft\u003cstrong\u003e\u0026nbsp;J-MD, NW, VL:\u0026nbsp;\u003c/strong\u003edata curation\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003epreparation, experiments\u003cstrong\u003e\u0026nbsp;MJ:\u0026nbsp;\u003c/strong\u003eformal analysis\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003ewriting\u003cstrong\u003e\u0026nbsp;-\u0026nbsp;\u003c/strong\u003ereview and editing, supervision\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBeitollahi, H., Jahani, S., Tajik, S., Ganjali, M.R., Faridbod, F., Alizadeh, T., 2019. 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Innov. 25, 102189. https://doi.org/10.1016/j.eti.2021.102189\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-sciences-europe","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"eseu","sideBox":"Learn more about [Environmental Sciences Europe](http://enveurope.springeropen.com)","snPcode":"12302","submissionUrl":"https://submission.nature.com/new-submission/12302/3","title":"Environmental Sciences Europe","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Electrochemical advanced oxidation processes (EAOPs), HPLC-HRMS, electrochemical oxidation, electrolysis flow cell, boron-doped diamond electrode, EU watchlist","lastPublishedDoi":"10.21203/rs.3.rs-6079652/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6079652/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe antidepressant venlafaxine and its metabolite o-desmethylvenlafaxine are frequently found in water bodies around the world reaching several micrograms per liter. As a remedy, electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation with a boron doped diamond (BDD) electrode have proven to be a suitable means to prevent entrance in the aquatic environment. For potential application, optimization of the EAOPs can be readily achieved by variation of the conditions using a flow cell as compared to a batch-mode cell. Monitoring and characterization of the reactants provide inside into the oxidation mechanism.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHigh performance liquid chromatography and high-resolution mass spectrometry led to the observation of five transformation products of venlafaxine and to four of o-desmethylvenlafaxine. Mass voltammograms were recorded from which the impact of the oxidation conditions on the degradation and the quantity and nature of transformation products were derived. The transformation pathways were identified as well. Detailed analysis revealed that hydroxyl radicals played the major role in the electrochemical oxidation of venlafaxine and o-desmethylvenlafaxine. The prevalence of the hydroxyl radical induced degradation was further corroborated by the radical scavenger \u003cem\u003etert\u003c/em\u003e-butanol, causing a decrease in elimination efficiency. Both drugs were best eliminated at pH 3 and a voltage of 1.5 V, with the least ecotoxicological concern as indicated by QSAR analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study shall contribute to the advancement of EAOPs for advanced stages in wastewater purification treatment. An \u003cem\u003ein silico\u003c/em\u003e ecotoxicity assessment using QSAR analysis showed that electrochemical oxidation is beneficial from an ecotoxicological point of view. Especially products formed via the indirect hydroxyl radical-induced mechanism showed a lower ecotoxicity than the initial compound.\u003c/p\u003e","manuscriptTitle":"Monitoring of the electrochemical oxidation of venlafaxine and its metabolite o- desmethylvenlafaxine using a flow cell and high-resolution mass spectrometry","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-30 07:05:51","doi":"10.21203/rs.3.rs-6079652/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-19T20:59:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-12T19:33:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-06T09:17:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"72489194978179563891713318435131932178","date":"2025-04-29T14:04:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-28T12:10:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"147101129891071066905949002136906691116","date":"2025-04-28T11:29:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"288103769387751264443898079241752966498","date":"2025-04-28T08:20:35+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-27T08:34:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-17T10:23:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Sciences Europe","date":"2025-04-16T08:38:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-sciences-europe","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"eseu","sideBox":"Learn more about [Environmental Sciences Europe](http://enveurope.springeropen.com)","snPcode":"12302","submissionUrl":"https://submission.nature.com/new-submission/12302/3","title":"Environmental Sciences Europe","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"efa983a2-428b-4f8a-8a01-5a8b8ff9d194","owner":[],"postedDate":"April 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T16:04:08+00:00","versionOfRecord":{"articleIdentity":"rs-6079652","link":"https://doi.org/10.1186/s12302-025-01169-8","journal":{"identity":"environmental-sciences-europe","isVorOnly":false,"title":"Environmental Sciences Europe"},"publishedOn":"2025-07-10 15:57:54","publishedOnDateReadable":"July 10th, 2025"},"versionCreatedAt":"2025-04-30 07:05:51","video":"","vorDoi":"10.1186/s12302-025-01169-8","vorDoiUrl":"https://doi.org/10.1186/s12302-025-01169-8","workflowStages":[]},"version":"v1","identity":"rs-6079652","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6079652","identity":"rs-6079652","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}