Environmental screening via timsTOF MS: A new dimension for discrimination and improved sensitivity in the detection of PFOS pollutants

Importance of the topic

Environmental water analysis is confronted by complex sample matrices containing numerous chemical and biological substances. Among these, PFOS compounds are high-priority pollutants due to their environmental persistence and known adverse health impacts. Accurate detection and isomeric discrimination are essential for reliable monitoring, source attribution and regulatory compliance.

Objectives and Overview of the Study

This work evaluates the use of Bruker’s TargetScreener liquid chromatography method combined with trapped ion mobility spectrometry on the timsTOF Pro platform. The aim is to achieve rapid separation and improved sensitivity in detecting four PFOS isomers at trace levels in environmental water samples.

Methodology and Instrumentation

The analytical workflow integrates high-performance LC, trapped ion mobility separation and high-resolution QTOF mass spectrometry. Key aspects include:

• Liquid chromatography using the TargetScreener LC protocol for PFOS analysis
• Trapped ion mobility spectrometry (TIMS) on the timsTOF Pro system to separate isomeric species based on collisional cross section (CCS)
• High-resolution QTOF mass analysis with external calibration (sodium clusters and Agilent tune mix) for accurate mass and mobility measurements
• Alternating MS and bbCID acquisition to collect precursor and fragment ion data

Main Results and Discussion

The combined LC-TIMS-QTOF approach provided:

• Resolution of co-eluting PFOS isomers that could not be fully separated by LC alone, as evidenced by mobility-filtered extracted ion chromatograms.
• Reproducible CCS measurements matching literature values with high accuracy, enabling an additional dimension for compound identification.
• Mass accuracy between 0.1–2 ppm and isotopic pattern fits (mSigma < 12), ensuring confident assignment of target analytes.
• Enhanced sensitivity in MS mode with ion mobility filtering, lowering detection limits and increasing signal-to-noise ratios by over tenfold.
• Improved visualization of diagnostic fragment ions in bbCID mode when filtered by mobility, facilitating both targeted screening and retrospective discovery workflows.

Benefits and Practical Applications of the Method

• Reliable discrimination of PFOS isomers supports detailed environmental forensics and risk assessment.
• Lower quantitation limits and high selectivity meet stringent regulatory requirements for water quality monitoring.
• Applicability to complex environmental samples in both routine targeted analyses and non-targeted screening.
• Comprehensive data archiving enables future reevaluation of samples for emerging contaminants.

Future Trends and Potential Applications

Emerging directions include expanding the approach to other PFAS classes, developing extensive CCS libraries for rapid compound identification, integrating real-time data processing and artificial intelligence algorithms, and adapting portable TIMS systems for on-site environmental surveillance.

Conclusion

The integration of liquid chromatography with trapped ion mobility on the timsTOF Pro platform introduces a powerful separatory dimension, markedly improving isomeric discrimination, mass accuracy, and sensitivity in PFOS pollutant screening. This methodology offers robust and adaptable solutions to meet current and future demands in environmental monitoring.

References

1. United States Environmental Protection Agency. EPA 822-R-16-002 (2016).
2. Lau C. Perfluorinated Compounds: An Overview. In Toxicological Effects of Perfluoroalkyl and Polyfluoroalkyl Substances, Humana Press, Cham, 2015, pp.1-21.
3. European Union. Regulation (EU) 2019/1021 on persistent organic pollutants, OJ L (2019).
4. European Commission. Proposal for Directive on water quality for human consumption, COD No 0332 (2017).
5. US EPA. PFAS Action Plan (EPA 823-R-18-004, 2019).
6. Dodds J.N. et al. Rapid Characterization of PFAS by IMS-MS, Anal Chem 92:4427-4435 (2020).