Large Volume Direct Injection Method for the Analysis of Perfluorinated Alkyl Substances (PFAS) in Environmental Water Samples in Accordance with ASTM 7979-17

Importance of the topic

Perfluorinated alkyl substances (PFAS) are persistent, bioaccumulative and potentially toxic chemicals used in a wide range of industrial and consumer applications. Their ubiquity in firefighting foams, food‐contact coatings and other products leads to widespread environmental contamination. Low part‐per‐trillion detection in water is required for regulatory compliance under U.S. EPA rules and EU directives, making sensitive and high‐throughput analytical methods essential.

Study objectives and overview

This work implements the ASTM 7979-17 large‐volume direct injection method for 39 PFAS analytes in various environmental waters. The approach extends the standard list of 21 PFAS compounds by including emerging replacements (ADONA, 9Cl-PF3ONS, 11Cl-PF3OUdS), combining them into a single, robust LC-MS/MS protocol. The study evaluates method detection limits, linearity, recovery, precision and applicability across five water matrices.

Methodology and instrumentation

The method employs a Waters ACQUITY UPLC I-Class system fitted with the PFAS Analysis Kit, an ACQUITY UPLC CSH Phenyl Hexyl column (1.7 µm, 2.1 × 100 mm) and a PFC isolator. Detection uses a Xevo TQ-XS triple quadrupole MS in negative ESI mode. Mobile phases are water:methanol (95:5) + 2 mM ammonium acetate (A) and methanol + 2 mM ammonium acetate (B) with a gradient over 22 min. Sample preparation involves spiking 5 mL water with isotopic surrogates, methanol addition, dual‐stage filtration, acidification and direct injection. MRM transitions and collision parameters were optimized using QuanOptimize.

Main results and discussion

Method detection limits ranged from 0.8 to 2.6 ng/L for most compounds, well below the 10 ng/L reporting limit in ASTM 7979-17. Calibration curves were linear (R² > 0.99). Recoveries in reagent, ground, surface, influent and effluent waters generally fell between 82 % and 120 %, meeting the 70–130 % criterion; only long‐chain PFTriDA, PFTreDA and FDEA showed matrix‐induced enhancement. Intra‐method and instrument reproducibility yielded RSDs < 10 %. All target PFAS were detected at spike levels in five matrices, and control samples met ASTM quality requirements except for 6:2 FTS, affected by solvent background.

Benefits and practical applications

The direct injection protocol minimizes preparation time and consumables, improving throughput and reducing contamination risks. Low ng/L sensitivity supports regulatory monitoring of PFAS in non‐drinking environmental waters under U.S. EPA Safe Drinking Water and Clean Water Acts, as well as EU Water Framework Directive obligations. The method’s robustness and fidelity make it suitable for routine QA/QC, research monitoring and industrial compliance.

Future trends and opportunities

Future developments may include expansion of analyte panels to cover novel PFAS and transformation products, integration with high-resolution accurate mass screening for suspect or non‐target compounds, continued refinement of contamination control in sampling and analysis, and automation of sample handling. Further correlation of PFAS levels with toxicological endpoints and fate studies will inform risk assessments and guide regulatory standards.

Conclusion

The ASTM 7979-17 large‐volume direct injection LC-MS/MS method on the Xevo TQ-XS achieves low‐ng/L detection, high linearity and robust recoveries across diverse environmental matrices. It meets or exceeds regulatory requirements for PFAS monitoring, offering a reliable, streamlined workflow for laboratories engaged in environmental analysis and compliance.

Reference

1. Secretariat of the Stockholm Convention: Stockholm Convention on Persistent Organic Pollutants.
2. U.S. EPA: Third Unregulated Contaminant Monitoring Rule (UCMR3).
3. U.S. EPA: PFOA & PFOS Drinking Water Health Advisories.
4. Directive 2013/39/EU of the European Parliament and Council on priority substances in the water environment.
5. ASTM D7979-17: Standard Test Method for Determination of PFAS in Water by LC-MS/MS.
6. L. Mullin and J. Burgess: Ultra Low-Level Detection of PFASs Using the PFAS Analysis Kit, Waters Technology Brief 720005701EN (2016).