DETERMINATION OF LEGACY AND EMERGING PERFLUOROALKYL SUBSTANCES (PFAS) IN WATER SAMPLES USING LC-MS/MS

Importance of the Topic

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants used in coatings, surfactants and firefighting foams.
Their widespread use and stability lead to accumulation in water sources, raising concerns about human health and environmental safety.
Sensitive and reliable analytical methods are essential to detect both legacy PFAS (PFOS, PFOA) and emerging analogues at trace levels.

Objectives and Overview of the Study

This study presents an expanded LC-MS/MS workflow to determine 40 native and 28 isotope-labelled PFAS compounds in various water matrices.
The goal was to achieve sub-ppt detection limits and robust quantification in surface, groundwater, influent and effluent wastewater.
The method follows ISO 25101 guidelines for sample enrichment and applies a targeted MRM approach for comprehensive PFAS coverage.

Methodology and Instrumentation

• Sample Preparation: 250 mL water samples collected in HDPE bottles underwent solid phase extraction (SPE) using Oasis WAX cartridges (6 cc, 150 mg).
  The protocol included pH adjustment to <3, conditioning, loading, rinsing and elution steps adapted from ISO 25101, yielding a 250× enrichment.
• Liquid Chromatography: ACQUITY UPLC I-Class Plus system fitted with a PFC kit, using a BEH C18 column (2.1×100 mm, 1.7 µm) maintained at 35 °C and sample tray at 10 °C.
  Gradient elution employed water:methanol (95:5) + 2 mM ammonium acetate (A) and methanol + 2 mM ammonium acetate (B) at 0.3–0.4 mL/min.
• Mass Spectrometry: Xevo TQ-S micro triple quadrupole with electrospray ionization in negative mode.
  Key parameters: capillary voltage 0.5 kV, desolvation 350 °C/900 L/hr and cone gas 100 L/hr. MRM transitions optimized via QuanOptimize in MassLynx.

Main Results and Discussion

• Recovery and Repeatability: Corrected recoveries (using isotopically labelled standards) ranged from 75–130% for most PFAS; PFBA and 6:2 FTS showed elevated recoveries due to laboratory background.
  %RSD for six replicate groundwater extracts remained below 15%, with most compounds under 10%.
• Detection Limits and Linearity: In-sample LODs spanned <0.01 to 8 ng/L, meeting advisory limits (US EPA 70 ng/L for PFOS/PFOA and EU sub-ppt targets).
  Linearity (R2) exceeded 0.988 for all analytes.
• Instrument Robustness: Twenty consecutive injections of spiked surface water showed <10% RSD in peak area, stable retention times and consistent ion ratios, confirming system durability in complex matrices.
• Environmental Sample Analysis: Surface, ground, influent and effluent waters revealed distinct PFAS profiles and concentration ranges, highlighting the method’s applicability to diverse matrices.

Benefits and Practical Applications of the Method

This workflow delivers high sensitivity and broad PFAS coverage, aligning with regulatory requirements.
It is suitable for environmental monitoring, compliance testing and routine QA/QC in laboratories concerned with both legacy and emerging PFAS.

Future Trends and Potential Applications

As regulatory scrutiny expands to include novel PFAS, analytical methods will evolve to screen larger compound libraries at ultra-trace levels.
Advances may include high-resolution mass spectrometry, automated sample preparation and integration of suspect screening for unknown PFAS.

Conclusion

The described SPE-LC-MS/MS method using Oasis WAX and the Xevo TQ-S micro system provides a comprehensive, sensitive and reproducible approach for quantifying a wide array of PFAS in environmental waters.
Its performance meets current advisory guidelines and demonstrates robustness across various sample types.

Reference

• Kari Organtini, Ken Rosnack, Douglas Stevens, Euan Ross and Eimear McCall. Waters Application Note 720006471EN, Waters Corporation (2019).