DIRECT INJECTION SCREENING METHOD FOR PER-AND-POLYFLUOROALKYL SUBSTANCES IN DRINKING WATER USING A PROTOTYPE BENCHTOP MULTI- REFLECTING TIME-OF-FLIGHT

Significance of the Topic

Per- and polyfluoroalkyl substances (PFAS) have seen extensive use in industrial and consumer applications, leading to persistent environmental contamination and potential human health risks. Traditional targeted analyses often fail to detect emerging or non-regulated PFAS, making high-resolution, non-targeted screening methods essential for comprehensive monitoring of drinking water.

Study Objectives and Overview

This study presents a direct injection screening workflow for both regulated and novel PFAS in drinking water. Utilizing a prototype benchtop multi-reflecting time-of-flight (MRT) mass spectrometer combined with UPLC, the work evaluates instrument performance (accuracy, resolution, sensitivity, dynamic range) and demonstrates a software-driven non-targeted screening process alongside quantitative capability.

Methodology

• Sample Preparation: 10 µL direct injection of spiked drinking water into polypropylene autosampler vials.
• Chromatography: Waters ACQUITY Premier UPLC with PFAS solution installation kit; BEH C18 column (2.1 × 100 mm, 1.7 µm); gradient from 95:5 to 5:95 water/methanol (2 mM ammonium acetate); 0.3 mL/min flow; column at 35 °C; sample tray at 6 °C.
• Mass Spectrometry: Negative ion MSE acquisition across m/z 50–1200 Da at 10 Hz; optimized source settings (capillary 0.5 kV, cone 10 V, source 120 °C, desolvation 250 °C); low/high collision energies for structural information.
• Data Processing: waters_connect platform with UNIFI application for peak picking, isotope and adduct clustering, retention time alignment, mass defect filtering and library searching.

Instrumental Setup

Waters ACQUITY Premier UPLC system with PFAS kit
Waters Xevo MRT benchtop multi-reflecting time-of-flight mass spectrometer
waters_connect software platform with UNIFI application

Main Results and Discussion

The Xevo MRT achieved mass accuracy better than ±300 ppb and resolution exceeding 75 000 at m/z 556.2765. Perfluorooctanesulfonic acid (PFOS) was detected at 30 ng/L with ±100 ppb accuracy and signal-to-noise above 17. Quantification was linear from 20 ng/L to 5000 ng/L (R² = 0.9933). The non-targeted workflow effectively filtered components by retention time and mass defect, enabling discovery of both known and novel PFAS. A dynamic range spanning over three orders of magnitude supported both screening and quantitative analyses.

Benefits and Practical Applications

• Bypasses time-consuming SPE and reduces reliance on specific standards through direct injection and non-targeted approaches.
• Allows retrospective data mining for emerging PFAS without prior compound knowledge.
• Supports high-throughput routine monitoring in environmental and drinking water laboratories.
• Integrates non-target screening, discovery, and quantification in a single software platform.

Future Trends and Applications

• Increasing injection volumes or on-line preconcentration to enhance trace-level sensitivity.
• Expansion of mass spectral libraries and incorporation of machine learning for automated PFAS identification.
• Application of workflows to complex matrices such as wastewater, soils, and biota.
• Advancements in source and transmission optimization to further improve sensitivity and resolution.

Conclusion

The direct injection screening method using a benchtop Xevo MRT TOF mass spectrometer and ACQUITY Premier UPLC provides a robust, accurate, and high-resolution solution for both targeted and non-targeted PFAS analysis in drinking water. Its streamlined sample preparation, wide dynamic range, and integrated software tools make it ideal for environmental monitoring and regulatory compliance.

Reference

1. U.S. Environmental Protection Agency. CompTox Chemicals Dashboard. https://comptox.epa.gov/dashboard/chemical-lists/pfasmaster (accessed November 2023).
2. Khoury-Hollins H., Riba I., Kirk J. Optimization of Source and Transmission Parameters for a Mix of Labile and Stable Per–Or Polyfluoroalkyl Substances (PFAS) Using the Xevo G3 QTof Mass Spectrometer. Waters Application Note 720008118-en, 2024.
3. Khoury-Hollins H., Reid L., Adams S. Direct Injection Screening Method for Per and Polyfluoroalkyl Substances (PFAS) in Drinking Water Using the High Resolution Time of Flight Mass Spectrometer, the Xevo G3 QTof. Waters Application Note 720008198-en, 2024.
4. Twohig M., Fujimoto G., Mohan A., Organtini K.L., Rosnack K.J., Hird S. Approaches to Non-targeted Analyses of Per- and Polyfluoroalkyl Substances (PFAS) in Environmental Samples. Waters Application Note 720007184, 2021.
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