Analysis and Quantitation of Polyfluorinated Alkyl Substances (PFAS) in EPA Method 537.1 Using High Resolution Accurate Mass Spectrometry

Significance of the Topic

The presence of per- and polyfluoroalkyl substances (PFAS) in drinking water is a major environmental and public health concern. High-resolution accurate mass spectrometry enables both reliable quantitation of regulated PFAS and the identification of emerging or unknown PFAS compounds that may pose additional risks.

Objectives and Study Overview

This study demonstrates the application of EPA Method 537.1 on a quadrupole time-of-flight (QTOF) mass spectrometer coupled with UHPLC. The goals include comparing quantitation limits with a triple quadrupole instrument, validating analytical performance at low parts-per-trillion levels, and establishing a workflow for tentatively identifying unknown PFAS in environmental samples.

Methodology and Instrumentation

The method follows the chromatographic conditions of EPA 537.1 with a delay column and an analytical column to separate PFAS. Electrospray ionization in negative mode was optimized on a triple quadrupole and transferred to the QTOF. Data acquisition included multiple reaction monitoring (MRM) on the QQQ and high-resolution MRM on the QTOF, while mass accuracy and isotopic patterns were used for non-target screening.

Used Instrumentation

• Shimadzu Nexera-X2 UHPLC system with Shim-pack XR-ODS delay column (50 mm × 2 mm × 2.2 µm) and Shim-pack TM Velox analytical column (150 mm × 2.1 mm × 2.7 µm)
• Shimadzu LCMS-8045 triple quadrupole mass spectrometer for method development and quantitation
• Shimadzu LCMS-9030 quadrupole time-of-flight (QTOF) mass spectrometer for high-resolution accurate mass analysis
• Electrospray ionization (ESI) source in negative mode with optimized source and interface temperatures

Main Results and Discussion

Quantitative performance of the QTOF at 25 ppt showed recoveries within acceptable ranges (80–129 %) and precision (RSD < 15 %) comparable to the triple quadrupole, with limits of quantitation below 3 ng/L for most PFAS. High-resolution data enabled a streamlined four-step workflow for unknown PFAS identification: feature detection, blank subtraction, formula prediction, and confirmation against DSSTox database entries using accurate mass and MS/MS spectra. Chromatograms demonstrated clear separation and detection of both regulated PFAS (e.g., PFOA, PFOS, GenX) and novel compounds like ADONA and chlorinated PFAS.

Benefits and Practical Applications

• Comparable quantitative results to conventional triple quadrupole methods with r² > 0.99 across calibration curves
• Expanded capability to screen for and tentatively identify non-target PFAS without additional runs
• Streamlined workflow integrating quantitative and qualitative analyses in a single sequence
• Enhanced laboratory efficiency for regulatory compliance, environmental monitoring, and QA/QC programs

Future Trends and Potential Applications

Advances in high-resolution mass spectrometry, software for formula prediction, and spectral libraries will accelerate non-target PFAS screening. The integration of machine learning and comprehensive suspect lists promises faster identification of emerging contaminants. Expanded environmental databases will support more robust risk assessments and inform regulatory policies.

Conclusion

This work confirms that a UHPLC-QTOF platform can meet the stringent requirements of EPA Method 537.1 for targeted PFAS quantitation while offering significant added value through high-resolution screening of unknown PFAS. Laboratories can leverage this dual capability to enhance water quality assessments and support ongoing environmental protection efforts.

References

1. EPA Method 537 rev 1.1, Determination of Selected Perfluorinated Alkyl Acids in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS), U.S. Environmental Protection Agency, 2009.
2. EPA Method 537.1, Determination of Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS), U.S. Environmental Protection Agency, 2018.