BOOK OF ABSTRACTS 57 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Analysis and Characterization SL22 Characterizing Organic Matter through FunctionalGroup-Based Approach: Quantification of Nitro Compounds Formed during Ozonation Valentin Rougé1,2, Nguyen Cong-Hau2, Pham Thi Thai Ha Nguyen2, Hyunjin Kim2, Taekeun Son2 and Yunho Lee2 1 Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dü bendorf, Switzerland, valentin.rouge@eawag.ch 2 Department of Environment and Energy Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea Water treatment with chemical oxidants is essential for disinfection and degradation of anthropogenic compounds. Yet, most of the oxidant reacts with the naturally occurring dissolved organic matter (DOM), forming potentially toxic products, typically addressed as disinfection by-products [1]. Despite decades of research on disinfection by-products, the oxidative transformation of DOM remains poorly understood due to analytical limitations. The fate of nitrogenous DOM is of particular concern, as known nitrogenous disinfection by-products are generally more toxic than other classes [2]. Monitoring specific disinfection byproducts provides a limited approach due to the complexity of the molecular structures that are responsible for the DOM-induced toxicity [3]. Instead, quantifying the bulk of specific functional groups within DOM offers a more comprehensive approach. Here, we present a functional-groupbased method to quantify oxidative modifications of nitrogenous DOM. We developed two photolysis-based approaches to quantify nitro compounds: (i) batch photolysis coupled with colorimetry for total nitro compounds, and (ii) liquid chromatography with post-column photolysis for individual compounds. Both methods use photolytic nitrite formation as a proxy for nitro compounds, with average molar nitrite yields of 68±17% for aliphatic compounds and 11±11% for aromatic compounds, enabling selective determination of aliphatic nitro compounds. Proof-of-concept ozonation experiment with model amines and amino acids demonstrated the applicability of the methods, providing new insights into γ-aminobutyric acid ozonation. When applying this method to DOM extracts and wastewaters, formation of nitro compounds during ozonation could be monitored. When combined with solid-phase extraction, aliphatic nitro compounds could be quantified down to a few nM in complex matrices. By combining the quantification of nitro and amine quantification, we could estimate for the first time that over 20% of amine-containing DOM moieties
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