Analysis of Legacy and Emerging Perfluorinated Alkyl Substances (PFAS) in Environmental Water Samples Using Solid Phase Extraction (SPE) and LC-MS/MS

Significance of the Topic

Perfluorinated alkyl substances (PFAS) are persistent, bioaccumulative anthropogenic chemicals widely used in non-stick coatings, firefighting foams and industrial processes. Their stability and mobility in aquatic environments have raised global health and regulatory concerns. Low reporting limits down to sub-ng/L levels are required to track both legacy PFAS (e.g. PFOS, PFOA) and emerging replacements (e.g. GenX) in drinking and surface waters.

Objectives and Study Overview

This work evaluates a workflow combining solid phase extraction (SPE) following ISO 25101 guidelines and sensitive LC-MS/MS analysis on a Waters Xevo™ TQ-S micro instrument. It aims to enrich and detect over 40 legacy and emerging PFAS in various environmental water matrices, and to demonstrate method performance in terms of sensitivity, recovery, linearity and robustness.

Used Instrumentation

• Waters ACQUITY™ UPLC™ I-Class PLUS with PFAS Analysis Kit (PFAS-free plumbing, isolator column)
• ACQUITY UPLC BEH C18 column (2.1 × 100 mm, 1.7 µm)
• Oasis™ WAX SPE cartridges (6 cc, 150 mg)
• Waters Xevo™ TQ-S micro triple quadrupole MS with ESI source
• MassLynx™ software with QuanOptimize™ and TrendPlot™ tools

Methodology and Instrumentation

Sample Preparation:
Water samples (250 mL) were acidified to pH < 3, filtered if needed, then loaded onto Oasis WAX cartridges. A wash step and elution with methanolic ammonium solution delivered a 250× enrichment. Eluates were dried under N₂, reconstituted in aqueous methanol and spiked with isotopically labeled standards.

LC Conditions:
Gradient elution using 95:5 water:methanol with 2 mM ammonium acetate (A) and methanol with 2 mM ammonium acetate (B). Flow ramped from 0.3 to 0.4 mL/min over a 22-minute run at 35 °C.

MS/MS Conditions:
Electrospray negative mode; capillary 0.5 kV; desolvation 350 °C (900 L/h N₂); cone gas 100 L/h; source 100 °C. MRM transitions and collision energies were optimized for each PFAS.

Main Results and Discussion

• Detection Limits: In-sample limits ranged from <0.01 to 2 ng/L, with many compounds at sub-ng/L (ppt) or even pg/L (ppq) levels, supporting regulatory targets (e.g. EU annual average 0.65 ng/L PFOS).
• Linearity: Calibration curves were linear over several orders of magnitude (R² ≥ 0.993).
• Recovery and Precision: Most PFAS showed 75–130 % average recovery. Method reproducibility in spiked ground water yielded RSDs <15 % for all analytes, often <10 %.
• Robustness: Twenty replicate injections of surface water extract produced <10 % RSD in peak area and stable retention times and ion ratios, ensuring reliable identification and quantitation in complex matrices.
• Environmental Samples: Four water types (surface, groundwater, influent and effluent wastewater) were analyzed. Up to 27 PFAS congeners were detected, with wastewaters showing the highest levels and diversity, and emerging PFAS identified alongside legacy compounds.

Benefits and Practical Applications

This SPE-LC-MS/MS workflow delivers:

• High sensitivity to meet or exceed global PFAS advisory limits
• Robust and reproducible quantitation across diverse water matrices
• Ability to monitor both regulated and emerging PFAS in routine environmental testing

Future Trends and Opportunities

Advancements may include automated on-line SPE, expanding target lists to novel PFAS derivatives, and adoption of high-resolution mass spectrometry for non-target screening. Improved sample enrichment strategies and standardized kits will further streamline low-level PFAS analysis.

Conclusion

Combining ISO 25101 SPE enrichment with the Xevo TQ-S micro LC-MS/MS platform provides a sensitive, reliable and flexible approach for comprehensive PFAS screening in environmental waters, addressing evolving regulatory and research needs.

Reference

1. EPA PFOA and PFOS Drinking Water Health Advisories. U.S. Environmental Protection Agency.
2. Directive 2013/39/EU of the European Parliament on Environmental Quality Standards for PFOS. European Commission.
3. Organtini K., Cleland G., Rosnack K. Large Volume Direct Injection Method for PFAS Analysis per ASTM 7979-17. Waters Application Note 720006329en, June 2018.
4. ISO 25101:2009 Water Quality – Determination of PFOS and PFOA via SPE and LC-MS. International Organization for Standardization.