DETERMINATION OF LEGACY AND EMERGING PERFLUOROALKYL SUBSTANCES IN GROUND AND SURFACE WATERS USING LC-MS/MS WITH DIRECT INJECTION

Significance of the Topic

Perfluoroalkyl substances (PFAS) are persistent environmental pollutants found in water, soil, and biota worldwide. Their unique chemical stability and bioaccumulative nature pose risks to human health and ecosystems. Regulatory agencies mandate detection at parts-per-trillion levels, driving the need for rapid, sensitive analytical methods that minimize contamination and maximize throughput.

Objectives and Overview

This study aimed to adapt the ASTM 7979-17 protocol for direct injection LC-MS/MS analysis of both legacy and emerging PFAS in ground and surface waters. By eliminating extensive sample cleanup, the method seeks to accelerate analysis while maintaining the sensitivity required for regulatory compliance and environmental monitoring.

Methodology and Instrumentation

Sample Pretreatment:

• Add 5 mL of water sample and 5 mL methanol into a 15 mL polypropylene vial.
• Filter the mixture through a PFAS-free syringe filter.
• Acidify and transfer to analysis vial without evaporation.

LC-MS/MS Conditions:

• LC system: ACQUITY UPLC I-Class Plus with PFC kit, ACQUITY CSH Phenyl Hexyl column (2.1×100 mm, 1.7 µm) at 35 °C.
• Mobile phases: A = 95:5 water:methanol + 2 mM ammonium acetate; B = methanol + 2 mM ammonium acetate; gradient from 100% A to 95% B over 17 min.
• MS system: Xevo TQ-XS, ESI mode (capillary voltage 1.0 kV, desolvation 500 °C, gas flows 1100 L/h and 150 L/h).
• MRM transitions optimized via QuanOptimize in MassLynx.

Results and Discussion

Method Detection Limits (MDLs) for most PFAS were in the low ng/L range, surpassing ASTM 7979-17 reporting thresholds; 6:2 FTS could not be quantified due to background contamination. Trueness, assessed with isotope-labelled surrogates, ranged from 80% to 125%. Repeatability across 20 injections showed <10% RSD for all detected analytes. Quality control samples met all criteria except for 6:2 FTS.

Practical Benefits and Applications

This streamlined approach significantly reduces sample handling and risk of PFAS introduction from laboratory consumables. The high throughput and sensitivity enable routine compliance testing for environmental monitoring and support fast decision-making in water quality assessment.

Future Trends and Applications

Further enhancements may include large-volume injection to lower detection limits, expansion to a broader spectrum of novel PFAS, integration of high-resolution MS for non-target screening, and portable LC-MS platforms for on-site analysis. Automated workflow and data processing tools will further improve efficiency.

Conclusion

The direct injection LC-MS/MS method based on ASTM 7979-17 provides rapid, sensitive, and reliable quantification of a wide array of PFAS in ground and surface waters. Its minimal sample preparation enhances throughput and reduces contamination risk, making it suitable for regulatory and research applications.

References

• Waters Application Note 720006329EN