Comprehensive Mass Spectrometry Workflows to Systematically Elucidate Transformation Processes of Organic Micropollutants: A Case Study on the Photodegradation of Four Pharmaceuticals

Organic micropollutants (OMPs) in the aquatic environment challenge conventional water treatment processes. Advanced oxidation processes, such as UV photolysis, serve as effective strategies to remove OMPs. However, these often yield unknown transformation products (TPs). High-resolution mass spectrometry (HRMS)-based non-target analysis (NTA) is commonly used to screen large numbers of chemicals but faces specific challenges such as low concentrations of compounds of interest, lack of reference standards, and the need for sophisticated data analysis workflows when used for TP identification. This article describes comprehensive workflows to study UV photolysis-related processes and the resulting TPs, by combining an automated photodegradation setup and HRMS and advanced NTA approaches. Four pharmaceuticals were successfully degraded in a case study, and 38 NTA features were effectively prioritized from complex sample matrices and identified as TPs through complementary approaches developed in this work. The identified TPs were structurally diverse and mostly novel. Semi-quantitation suggested that the TPs explained a relevant part of the parent removal. The developed workflows are a step toward systematic comprehensive analysis of transformation processes in water and beyond. The openly available data-processing tools and data enhance transformation data repositories and algorithms and support NTA studies in general.