Beyond target lists: direct injection liquid chromatography-tandem mass spectrometry for comprehensive monitoring of legacy and emerging per- and polyfluoroalkyl substances in water systems.

Per- and polyfluoroalkyl substances (PFAS) are a large and structurally diverse group of persistent contaminants widely detected in aquatic environments, creating significant analytical and regulatory challenges. This study presents a direct-injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of 51 PFAS, including legacy compounds and emerging alternatives, in groundwater, surface water, and tap water. By eliminating solid-phase extraction (SPE), the approach simplifies sample preparation, reduces solvent consumption, and minimises contamination risks associated with conventional workflows. The method showed consistent analytical performance, with limits of quantification ranging from 0.65 to 10 ng/L and matrix effects were maintained within ±20%, effectively corrected using isotope-labelled internal standards. Procedural blanks showed negligible contributions to target analyte signals, confirming low background contamination, while a delay column improved data reliability by separating system-derived PFAS from analyte signals. The method was suitable for a broad range of PFAS, including short-chain and structurally diverse compounds that are often difficult to quantify using traditional SPE-based methods. Overall, the proposed direct-injection LC-MS/MS method provides a reliable, efficient, and high-throughput alternative for comprehensive PFAS monitoring in tap, surface, and groundwater. By expanding analytical coverage beyond conventional targeted methods, it enables more representative assessment of PFAS occurrence and environmental risk, supporting future monitoring programmes and regulatory strategies.