Development of Screening Method for Targeted and Undiscovered Perand polyfluoroalkyl Substances (PFAS) in Surface Water on Q-TOF Mass Spectrometer

Significance of the Topic

The persistence and widespread occurrence of per- and polyfluoroalkyl substances (PFAS) in water bodies pose growing environmental and human health concerns. Traditional targeted analyses cover only a limited number of known PFAS, potentially overlooking novel or emerging analogues. A robust screening strategy that combines sensitive detection of both established and unknown PFAS is critical for comprehensive risk assessment and regulatory monitoring.

Study Objectives and Overview

This work aimed to develop and validate an integrated high-resolution screening method on a Q-TOF mass spectrometer for simultaneous targeted detection of known PFAS and discovery of novel PFAS in surface and groundwater. The approach combines a custom high-resolution mass spectrometry (HRMS) library for 34 PFAS, data-dependent acquisition (DDA), and a workflow leveraging characteristic mass defects and diagnostic fragment ions to flag unknown PFAS candidates.

Methodology

A mixed standard of 34 PFAS was prepared to build an HRMS library containing retention times, accurate masses and MS/MS spectra. Water samples were collected from rivers and groundwater, filtered and enriched 50-fold prior to analysis. Samples were analyzed in negative electrospray ionization mode using full-scan MS and DDA. Data processing involved targeted library matching and an untargeted screening workflow incorporating:

• Mass defect filtering (–10 to –80 mDa) to isolate PFAS-like ions based on characteristic negative mass defects resulting from extensive fluorination.
• Extraction of diagnostic fluorinated fragment ions (e.g. C2F5–, C3F7–) and functional group fragments (e.g. SO3–, FSO3–) from DDA spectra.
• Formula prediction and structural elucidation tools to assign plausible PFAS formulas and confirm structures.

Instrumental Setup

The analyses were carried out on a Shimadzu LCMS-9030 Q-TOF equipped with a heated ESI interface. Key parameters included:

• Column: Shim-pack GIST C18, 100×2.1 mm, 2 µm.
• Gradient: 10–95% acetonitrile over 35 minutes, total run time 45 minutes.
• Flow rate: 0.4 mL/min; column temperature 40 °C; injection volume 10 µL.
• Mass range: full scan with DDA in negative mode; collision gas argon (270 kPa).
• Mass accuracy: all 34 PFAS standards measured within ±3 ppm.

Main Results and Discussion

Targeted screening successfully detected several PFAS, including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), with spectral matching scores above 90% and mass errors below 0.2 ppm. In untargeted analysis, a candidate ion at m/z 382.9418 exhibited a mass defect of −58.2 mDa. Coincident peaks of C2F5– and C3F7– in DDA spectra and formula prediction suggested a formula C6F13SO2H. Structural analysis confirmed the presence of perfluorohexyl sulfinic acid or an isomeric analogue in the same water sample.

Benefits and Practical Applications

This integrated approach enables:

• Comprehensive surveillance of both regulated PFAS and previously uncharacterized compounds in environmental waters.
• Efficient prioritization of suspect features for further confirmation without exhaustive manual review.
• Improved confidence in PFAS identification through combined high mass accuracy, diagnostic fragments and retention time matching.

Future Trends and Potential Uses

Ongoing advances in HRMS hardware and data processing algorithms will further enhance sensitivity and throughput of PFAS screening. Expanded in-house or public HRMS libraries, machine-learning–based prediction of fragmentation patterns, and improved open-source workflows will facilitate large-scale monitoring. The described workflow can be adapted to other complex environmental matrices and extended to emerging halogenated contaminants.

Conclusion

A dual targeted and untargeted PFAS screening method on Q-TOF LC-MS has been demonstrated to effectively detect known PFAS and reveal novel fluorinated substances in surface waters. The combination of an HRMS library, mass defect filtering and diagnostic fragment extraction offers a powerful framework for comprehensive PFAS monitoring.

References

1. Shoemaker J., Tettenhorst D. Method 537.1: Determination of Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by SPE and LC-MS/MS. US EPA, 2018.
2. EPA Researchers Use Innovative Approach to Find PFAS in the Environment. US EPA Science Matters, 2019.
3. Liu Y. et al. High-resolution MS methods for non-target discovery of PFAS in environmental and human samples. Trends Anal. Chem., 2019.