(C) PLOS One
This story was originally published by PLOS One and is unaltered.
 . . . . . . . . . .



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 [1]

['Deepak Timalsina', 'Department Of Chemistry', 'College Of Liberal Arts', 'Sciences', 'The University Of Kansas', 'Lawrence', 'Kansas', 'United States Of America', 'Bhargavi Srija Ramisetty', 'Department Of Pharmaceutical Chemistry']

Date: 2026-05 

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.

Funding: This study was supported in part by a pilot project award from the University of Kansas General Research Fund (2504120 to MZW), the Center for Targeted PFAS Analysis (PFAS Lab) at the University of Kansas, and a research grant (G25AP00168 to MZW) from the United States Geological Survey. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. DT and MZW received salary from the University of Kansas and the grant from the United States Geological Survey.

Introduction

Per- and poly-fluoroalkylated substances (PFAS) consist of at least one perfluoro (-CF 3 ) or polyfluoro (-CF 2 ) alkyl group in their chemical structures [1, 2] and common PFAS contain a perfluoroalkyl chain (C n F 2n+1 ) with a polar terminal functional group, such as -COOH, -SO 3 H, -SO 2 NH 2 . PFAS are called “forever chemicals” due to their resistance to degradation in the environment. This higher thermodynamic, metabolic, and environmental stability is partly due to the high C-F bond strength (488 kJ/mol vs 413 kJ/mol for the C-H bond) in the alkyl chain [3]. The C-F chain lengths also influence the surfactant properties, making it a good repellent to oils and greases. This makes PFAS suitable for use in protective coatings [4–7], textiles [8], paints [9], adhesives [10], food wrappers, cookware, and cosmetics [11–14]. PFAS are widely used in firefighting foam [15,16], semiconductors, insecticides, and space materials [17]. PubChem, one of the largest chemical database collections, recorded over 7 million PFAS as of September 2022 [18]. Due to their extensive usage and persistence, these compounds are distributed widely in the environment. Once released, these compounds can travel through the water system and atmospheric pathways, leading to contamination in places far away from the sources, such as Arctic and Antarctic glaciers [19]. Recent studies report the prevalence of PFAS in soil [20], water [21,22], food, and consumer products from parts per trillion (ppt) to higher parts per billion (ppb) levels [23] and the United States Geological Survey (USGS) reported that individual PFAS concentrations ranged from 0.025 to 319 ppt (ng/L) in >600 point-of-use tapwater samples and estimated that at least one PFAS could be detected in about 45% of US drinking-water samples [24].

PFAS are of increasing concern due to their toxicity and potential for bioaccumulation. Studies have shown that these PFAS, such as PFOA and PFOS, are linked to several health issues, such as fetal development, suppression of vaccine response, thyroid disease [25,26], kidney cancer, and testicular cancer [27]. A study done in mice showed that PFOA affects metabolic pathways, accumulates in the brain, and alters the neurotransmitter level and synaptic formation [28]. Even low concentrations of PFAS are of concern due to their accumulation inside the human body. For example, PFOA has been found to accumulate in the body due to renal tubular reabsorption and enterohepatic recirculation [29–32]. The half-life of PFOA in humans has been estimated to range from 1.2 to 14.9 years [33–35].

Due to these potential health risks, the United States Environmental Protection Agency (US EPA) announced the National Primary Drinking Water Regulation (NPDWR) on April 10, 2024 for six PFAS and established legally enforceable levels, known as Maximum Contaminant Levels (MCLs) in drinking water [36]. The MCLs are 4 ppt (or ng/L) for PFOA and PFOS, and 10 ppt for PFHxS, PFNA, and HFPO-DA (commonly known as GenX chemical), and a Hazard Index of 1 for the combined and co-occurring levels of PFHxS, PFNA, HFPO-DA, and PFBS. Importantly, EPA also finalized health-based, non-enforceable Maximum Contaminant Level Goals (MCLGs) to be zero for PFOA and PFOS, 10 ppt for PFHxS, PFNA, and HFPO-DA, and a Hazard Index MCLG of 1 for the mixtures. As of January 12, 2026, the European Union (EU) has implemented a new EU-wide rule on the systematic monitoring of PFAS in drinking water to ensure compliance with the new EU limit values under the recast Drinking Water Directive [37]. The new rule established clear limit values to ensure drinking water contains no more than 500 ppt of total PFAS and 100 ppt of the sum of 20 individual PFAS [38]. Stricter limits are expected to follow in the coming years as individual EU member states like Germany and Denmark have opted for lower limit values to better protect against PFAS [39]. Similarly, the World Health Organization (WHO) issued provisional guidance values of 100 ppt individually for PFOA and PFOS in drinking water and a combined 500 ppt for total PFAS based on the 29 PFAS compounds [40]. Although exact details of these regulations are subject to change, it is generally expected that public water systems must monitor and mitigate PFAS contamination and provide the public with information on the PFAS levels in their drinking water. To meet these demands (especially the MCLG of zero for PFOA and PFOS), a sensitive, reliable, and cost-effective analytical method to detect and quantify sub-ppt trace-level PFAS in the drinking water is urgently needed.

EPA has released two analytical methods based on solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) that are suitable for PFAS monitoring in the drinking water. The EPA Method 537.1 (Version 2.0; released in March 2020) was designed specifically for drinking water, targeting 18 PFAS. It utilizes SPE at the flow rate of 10–15 mL/min to preconcentrate the PFAS from a 250 mL starting sample volume, followed by N 2 drying of the eluate (<65°C) before LC-MS/MS analysis. In contrast, the EPA Method 1633A (released in December 2024) is a more comprehensive method covering diverse matrices (aqueous, solid, biosolids, and tissues), targeting 40 PFAS [41]. This method uses 500 mL starting sample volume with a reduced SPE flow rate of 5 mL/min without the use of N 2 drying before LC-MS/MS analysis. It utilizes the isotope-dilution or extracted internal standard quantification technique, which is recognized as the gold standard technique for achieving accurate quantifications.

Previous studies have reported the detection limit as low as 3.2 ppt for some of the PFAS using nano-electrospray ionization and high-resolution mass spectrometry (Nano-ESI-HRMS) following Method 537.1 [42]. The best detection limits recorded in other studies using either Method 1633A or 537.1 were about 1.04 - 20.98 ppt for some of the PFAS [43,44]. Although these reported detection limits are generally sufficient for monitoring MCLs for individual PFAS in drinking water, they are inadequate for MCLGs or monitoring mixtures which require sub-ppt detection limits. Furthermore, both EPA methods are quite time-consuming and laborious, requiring long SPE sample loading time (e.g., 17–25 min for a 250-mL sample using Method 537.1 and 100 min for a 500-mL sample using Method 1633A), substantially reducing the analytical throughput. To advance and expedite the PFAS analysis, several alternatives have been investigated, such as the total oxidizable precursor assay (TOP), analysis of adsorbable organofluorine and extractable organofluorine (AOF/EOF) [45]. These assays are non-specific, cannot speciate or quantify individual PFAS, and are associated with interference from other fluorinated compounds such as pesticides and pharmaceuticals. Paper spray mass spectrometry (PS-MS) also offered rapid analysis with higher sensitivity without the need for extensive sample preparation and chromatographic separation [46]. However, a lack of separation before the MS analysis can lead to analytical challenges when compounds with similar molecular weights are present in the sample. For instance, PFOS and taurodexycholic acid (TDCA) exhibit overlapping MRM transitions, resulting in a potential interference if not resolved properly before analysis [47].

[END]
---
[1] Url: https://journals.plos.org/water/article?id=10.1371/journal.pwat.0000501

Published and (C) by PLOS One
Content appears here under this condition or license: Creative Commons - Attribution BY 4.0.

via Magical.Fish Gopher News Feeds:
gopher://magical.fish/1/feeds/news/plosone/