Premium ultra-trace analytical method for part per quadrillion (ppq) PFAS quantification in drinking water
Wejdan Alghamdi1, Jordan M Partington2, Ivanhoe K H Leung3
1Australian Laboratory for Emerging Contaminants, School of Chemistry, University of Melbourne, Victoria, 3010, Australia; Department of Chemistry, College of Science, University of Bisha, Bisha, P.O. Box 551, 61922, Saudi Arabia.
Background:
Recent improvements in analytical methods have made it possible to detect very low levels of contaminants in drinking water, allowing for more accurate tracking of per-and polyfluoroalkyl substances (PFAS). This study optimized a sensitive sub ng/L method for the quantification of 75 PFAS (from 80 that were evaluated) in drinking water using solid phase extraction (SPE) and liquid chromatography triple quadrupole mass spectrometry (LCTQ). Based on USEPA 533/537 analytical methods for drinking water, the optimisation process included vial materials, evaporation parameters, and the selection of SPE sorbents and eluents. These conditions were then utilized to achieve ppq-level quantification for PFOS, PFOA, Gen-X, PFBS, PFNA, and PFHxS.
Results:
Addition of 20 % water as a keeper solvent following SPE and through evaporation increased analyte recovery, especially for semi-volatile PFAS. Sequential elution solvents of 4 mL 0.1 % NH4OH in MeOH/ACN (50:50 v/v) followed by 4 mL ACN, resulted in acceptable recoveries (70-130 %) of 75 legacy and emerging PFAS. The optimized method achieved limits of detection lower than previous similar studies, enabling quantification of PFAS at premium ultra trace pg/L levels ranging from 0.0038 to 0.0155 ng/L with recoveries ranging from 87 to 119 %. This optimized procedure was used on 27 drinking water samples from Victoria's Gippsland region in Australia, detecting 50 of the 75 targeted PFAS. Notably, 12 PFAS were detec in drinking water (tap and bottled) for the first time globally ( L-PFTrDS, 8Cl-PFOS, 10:2 FTUCA, MeFBSA, EtFOSA, EtFOSE, AP-FHxSA, TAMP-FHxSA, 8:2 Cl-PFESA, NFDHA, 8:8 PFPi and diSAmPAP). While most of the samples examined in the investigation did not pose a threat to human health based on the present standards, half of the collected samples had PFOS and PFOA concentrations higher than the advisory contaminant levels set by the US EPA in 2022 (4 pg/L).
Significance:
This work improves the efficiency of targeted PFAS analysis, enhancing the capabilities of monitoring a wide range of PFAS including legacy and emerging compounds, and contributing to public health safety. By optimizing the premium ultra trace pq/L levels, this methodology presents a valuable tool for PFAS assessment to meet regulation requirements in the future.
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