Rapid and Simple Evaporative Concentration Approach for the Analysis of Poly- & Perfluoroalkyl Substances (PFAS) in Potable Waters by Liquid Chromatography – High Resolution Orbitrap Mass Spectrometry

PFAS are a class of persistent organic pollutants with wide occurrence that have been linked to numerous negative health outcomes. Current maximum contaminant levels for 6 PFAS are 4-10 ng/L. To achieve the requisite sensitivity, almost all prescribed methods have relied upon selective preconcentration of PFAS from large volumes of water by solid phase extraction. In addition to being time consuming and laborious, care must be taken to minimize loss of PFAS to the various sampling surfaces and sample contamination due to their ubiquity in various lab supplies and solvents.
To overcome these limitations, PFAS were first concentrated directly in their sampling tubes (5-15 mL) by evaporation under nitrogen prior to detection by high resolution mass spectrometry (HRMS) on a quadrupole-orbitrap mass spectrometer. Loss by evaporation and precipitation of acidic PFAS was minimized by addition of Na4EDTA (pH 10.2). We also found that loss of PFAS occurred when <80% methanol was used for reconstitution prior to injection. Large volume injection was performed using an optimized sandwich injection with in-needle mixing without compromising separation efficiency for most PFAS. Detection in multiplexed single ion monitoring and full scan modes achieved instrumental limits of detection of <1 ng/L for most PFAS with no detectable interferents owing to the high resolving power of the mass spectrometer. In addition, full scan mode permits PFAS suspect screening and retroactive analysis simultaneously. 23 out of 24 target compounds had method detection limits that ranged from 0.02-0.62 ng/L, with spiked recoveries of 73.1 – 144.2%, 99.7% on average of 4 ng/L spike. We also discovered that heating Na4EDTA resulted in beneficial matrix effects for most PFAS (up to 276 %) with fluorotelomer sulfonates and sulfonadmidoacetic acids being the most affected. Sample preparation required <2 hrs per batch with 12 samples per batch greatly increasing throughput relative to conventional methods.