A DIRECT INJECT APPROACH FOR ANALYSIS OF LEGACY AND EMERGING PERFLUOROALKYL SUBSTANCES (PFAS) IN ENVIRONMENTAL WATER AND SOIL SAMPLES

Significance of the topic

Perfluoroalkyl substances (PFAS) represent a class of synthetic chemicals widely used in industrial and consumer products for their nonstick, surfactant, and water-resistant properties. Their persistence, bioaccumulative potential, and toxicity have led to global regulatory limits at parts-per-trillion (ppt) levels in environmental waters and soils. Reliable, high-throughput analytical methods are crucial for monitoring both legacy PFAS and emerging analogs to protect ecosystem and human health.

Objectives and study overview

This study evaluates a direct injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach for simultaneous analysis of over 30 legacy and emerging PFAS in diverse environmental matrices. The method aims to simplify sample preparation, increase throughput, minimize contamination, and achieve ppt-level detection in surface water, groundwater, influent/effluent streams, and soil types including sand, silt, and clay.

Methodology and instrumentation

Sample preparation relies on direct injection of minimally treated samples:

• Water samples: 5 mL aliquots in PFAS-compatible Eppendorf tubes; 30 µL injection.
• Soil samples: 2 g of spiked sand, silt, or clay in 15 mL tubes; aqueous extraction followed by injection.

Chromatography and detection details:

• LC system: ACQUITY UPLC I-Class Plus with PFAS kit.
• Column: CSH Phenyl Hexyl, 2.1 × 100 mm, 1.7 µm; column temperature 35 °C; sample temperature 10 °C.
• Mobile phases: A – 95:5 water:methanol + 2 mM NH4OAc; B – methanol + 2 mM NH4OAc; gradient from 100% A to 95% B over 17 min.
• MS system: Xevo TQ-XS, ESI negative mode, capillary 1.0 kV, desolvation 500 °C, cone gas 150 L/h, desolvation gas 1100 L/h.
• MRM transitions optimized via QuanOptimize; isotope-labeled surrogates for recovery correction.

Results and discussion

All target PFAS—including legacy carboxylates, sulfonates, telomer acids, and emerging compounds (e.g., GenX, ADONA)—were detected in both low- and high-level spikes:

• Water matrices: Recoveries for PFOS ranged 80–125%; PFOA and other analytes showed similar performance. Repeatability over 20 injections yielded <10% RSD.
• Soil matrices: PFOA recoveries varied between 70–130% across sand, silt, lean clay, and fat clay. Emerging PFAS mirrored legacy behavior.
• Sensitivity: Method detection limits in water were in the low ng/L range; in soils, ng/kg levels were achieved. GenX was quantified at 10 ng/L (vial) and 40 ng/kg (soil).

Benefits and practical applications

The direct injection workflow offers:

• Rapid turnaround due to minimal sample preparation.
• Reduced risk of PFAS background contamination from extraction sorbents or consumables.
• High sensitivity and robust quantitation across diverse environmental matrices.
• Compatibility with standardized methods such as ASTM D7979 and U.S. EPA guidelines.

Future trends and opportunities

Expanding the method to broader PFAS lists and complex matrices will support regulatory monitoring and research. Potential enhancements include:

• Integration of high-resolution MS for non-target screening and novel PFAS identification.
• Automated calibration strategies using matrix-matched and isotopic dilution approaches to mitigate matrix effects.
• Miniaturized, field-deployable LC-MS systems for on-site PFAS surveillance.

Conclusion

The large-volume direct injection LC-MS/MS method on the Xevo TQ-XS platform provides a sensitive, reliable, and efficient solution for determining both legacy and emerging PFAS in water and soil samples. It meets or exceeds method requirements and health advisory thresholds, offering a powerful tool for environmental monitoring and quality control.

Instrumentation used

• ACQUITY UPLC I-Class Plus with PFAS kit
• CSH Phenyl Hexyl column (2.1 × 100 mm, 1.7 µm)
• Xevo TQ-XS tandem quadrupole mass spectrometer