Achieving sub-part per trillion trace level PFAS quantification in drinking water using an optimized fast flow solid-phase extraction and UPLC-MS/MS method

Per- and poly-fluoroalkyl substances (PFAS) are not efficiently degraded and hence cycle through the environment, persist for a very long time, accumulate in living organisms, and cause potential health and ecological risks. PFAS monitoring in the drinking water relies on solid phase extraction (SPE) for sample concentration and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for sensitive and specific detection, but conventional methods suffer from long processing time, inadequate sensitivity for sub-part per trillion (ppt) trace level detection, and high cost. In this study, we aimed to develop and validate an optimized fast flow SPE method to achieve sub-ppt trace level quantification of 40 PFAS compounds that are of environmental concern to the US Environmental Protection Agency. The impact of several key sample preparation parameters, including N 2 drying, syringe filtration, SPE elution volume, and SPE flow rate, on the PFAS recovery was determined. These results helped inform the development of the final optimized fast flow SPE method, which was demonstrated using blank water samples spiked with trace levels of PFAS and tap water samples. The new fast flow SPE method substantially reduced the sample loading time (6 min for a 500-mL sample vs. 100 min required for normal flow SPE; 60–70 min for a 4-liter sample vs. 800 min required for normal flow SPE) without compromising the PFAS recovery for 38 out of 40 PFAS compounds and achieved sub-ppt (as low as 0.01 ppt for method detection limit) trace level quantification of PFAS in the drinking water. As a result, the optimized fast flow SPE is a viable strategy to enhance method sensitivity, increase throughput, and reduce cost for PFAS analysis and will positively impact future PFAS monitoring in the drinking water.