Data-Driven Discovery of Unknown Precursors of N-Nitrosodimethylamine in Nontargeted Liquid Chromatography-High...

N-Nitrosodimethylamine (NDMA) is a carcinogenic byproduct formed from nitrogen-containing organics during water disinfection. Identifying its precursors in source water is necessary for reducing or eliminating NDMA formation. Previous studies focused on model precursors with a dimethylamine group (DMA: -N(CH₃)₂), missing precursors without DMA that can form NDMA during chloramination. Here, we aimed to develop a new approach enhancing the discovery of various NDMA precursors. By analyzing MS/MS spectra of 39 model NDMA precursors, we identified three diagnostic fragment ions: [C₂H₆N]⁺, [C₂H₇N]^•+, and [C₂H₈N]⁺. Using these fragments to query the NIST23 MS/MS library revealed 763 candidate compounds. Among 21 commercially available candidates, seven were experimentally confirmed as NDMA precursors through chloramination─four with DMA moieties and three without. Additionally, five drugs lacking DMA were newly identified as NDMA precursors. To facilitate large-scale screening, we developed NitrosAmine Precursor eXplorer (NitraPreX) for nontargeted LC-HRMS analysis. When applied to analyze Suwannee River Humic Acid reference material and real local water samples, NitraPreX tentatively identified over 200 potential NDMA precursors and confirmed two non-DMA-containing compounds, hydroxychloroquine and N,N-bis(2-hydroxyethyl)dodecanamide, as NDMA precursors. This approach provides a robust framework for uncovering a wider range of NDMA precursors.