Perfluoroalkyl substances (PFAS) are a growing concern with an EPA Drinking Water Health Advisory level of 70 ng/L for PFOS plus PFOA, and proposed guidelines as much as 10 times lower in other jurisdictions.  The USGS National Water Quality Laboratory has developed LC/MS/MS methods for the determination of 34 of PFAS in surface water, groundwater, wastewater effluent, and other matrices. Target compounds include PFOS and PFOA, other sulfonates and carboxylates of varying chain length, and select precursors and synthetic substitutes (e.g., GenX, ADONA).<br/>Sample preparation was streamlined with no filtration and minimal sample handling; field samples (1 mL) collected directly into centrifuge tubes were amended with isotopically-labeled standards and methanol (~50% by volume), centrifuged, and supernatant transferred to polypropylene vials for analysis. Compounds were separated on a porous shell reversed-phase column with a methanol-water gradient and analyzed by multiple-reaction monitoring in negative electrospray mode with isotope-dilution quantitation.<br/>Method validation studies were conducted in groundwater, surface water, and wastewater effluent with replicates (n=7) spiked at multiple concentrations between 2 and 2000 ng/L. Recovery at intermediate concentration (145 ng/L) for 30 of 34 compounds ranged from 78.9 to 114.0% with RSDs less than 20.4%.  Each matrix was spiked (413 ng/L), refrigerated, and recoveries estimated after t=0, 7, 28, and 90 days. Maximum holding time (28 days) was set as the longest time with all compound recoveries above 70%. Method detection levels (MDLs) determined in reagent water using a multi-concentration statistical approach (ASTM’s DQCALC, 8 concentrations) ranged from 1.5 to 21.3 ng/L.

Determination of perfluoralkyl substances in water by direct injection of matrix-modified centrifuge supernatant and LC/MS/MS

ACS Spring 2022

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