Solving Analytical Challenges in PFAS Testing: Robust Calibration Data, Low Mass Confirmation and Isomer Quantification

Significance of the topic

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants under growing regulatory scrutiny. Accurate, reliable PFAS measurement is essential for environmental monitoring, compliance, and risk management. Key analytical challenges include: maintaining calibration stability under high-throughput workloads, confirming short-chain PFAS that yield weak or atypical product ions, and reporting branched versus linear isomers alongside total PFAS concentrations. Methods that extend calibration longevity and provide robust single-run confirmation and isomer quantification can substantially lower costs and increase laboratory throughput.

Objectives and study overview

• Evaluate the analytical robustness and long-term calibration stability of the Xevo TQ Absolute XR triple quadrupole mass spectrometer operated with waters_connect for Quantitation Software for routine PFAS testing.
• Test method performance across challenging matrices (surface water, landfill leachate, biosolids) during extended high-throughput sequences.
• Assess strategies for low-mass fragment confirmation of short-chain PFAS (e.g., PFBA, PFPeA) and procedures for separate quantitation/reporting of branched and linear isomers (PFHxS, PFOS).

Methodology and Instrumentation

• Analytes: a 42-analyte PFAS method with calibration curves generated using linear, 1/x weighted fits.
• Initial calibration quality: all calibrations produced relative standard error (%RSE) < 20%.
• Robustness testing: extended analytical sequences with continuous injections of environmental extracts (surface water, biosolids, landfill leachate); QC standards injected every ten matrix samples; QC acceptance set at ±30% versus initial calibration.
• Performance endpoints: calibration longevity, trueness and precision over time, isomer-specific quantitation, and confirmation capability for short-chain PFAS using low-mass fragments.

Instrumentation used

• Mass spectrometer: Waters Xevo TQ Absolute XR triple quadrupole MS.
• Software: waters_connect for Quantitation (enables enhanced transmission and detection of fragments below 50 amu and automated isomer reporting).
• Acquisition mode: multiple reaction monitoring (MRM) transitions including conventional quantifier/qualifier pairs and a low-mass confirmation ion (m/z 19, fluoride) for short-chain PFAS such as PFPeA; example PFPeA transitions reported: 262.90 > 219.00 (quantitation) and 262.90 > 19.00 (confirmation).

Main results and discussion

• Calibration robustness: Initial calibrations for 42 PFAS met quality criteria (%RSE < 20%). During extended sequences with continuous injections of complex matrices, the method maintained calibration integrity for up to five weeks when evaluated with QC injections every ten samples and a ±30% acceptance window.
• Trueness and precision: Trueness plots for the analytes remained within the ±30% tolerance over the extended period; precision (%RSD) reported for selected isomers was low (examples from the study indicate %RSD values in the low single-digit percent range), indicating stable quantitative performance.
• Isomer quantification: Separate calibration curves and reporting were successfully applied to branched and linear isomers of PFHxS and PFOS. waters_connect automated calculation and reporting of branched, linear, and total concentrations, with total analyte levels remaining consistent across the study period.
• Low-mass confirmation: Short-chain PFAS such as PFBA and PFPeA, historically considered difficult to confirm via low-mass product ions, produced a fluoride fragment at m/z 19. The software’s enhancement of fragment transmission below 50 amu enabled reliable detection of this ion across the calibration range, permitting single-run confirmation without requiring HRMS. Example chromatograms presented for PFPeA in landfill leachate show clear, integrable signals for both the quantifier and the m/z 19 confirmation transitions.
• Operational implications: The platform sustained analytical performance after very large numbers of injections, reducing the need for frequent recalibration, secondary confirmation runs, and unscheduled maintenance while preserving data quality in difficult matrices.

Benefits and practical applications

1. Regulatory and compliance testing: improved confidence in long-term quantitative results and isomer-resolved reporting supports regulatory requirements.
2. Laboratory efficiency: reduced frequency of calibration and confirmatory HRMS runs lowers analyst time, consumable use, and overall cost per sample.
3. Single-run confirmation: detection of low-mass fluoride fragments enables confirmation of certain short-chain PFAS within the same LC‑MS/MS run, streamlining workflows.
4. Applicability to complex matrices: validated performance across surface water, biosolids, and landfill leachate demonstrates practical utility for environmental monitoring programs.

Future trends and potential uses

• Broader adoption of optimized low-mass fragment detection for short-chain PFAS could reduce reliance on HRMS confirmation, but will require inter-laboratory validation and interference studies in diverse matrices.
• Integration with laboratory information management systems and automated QC trending will further increase throughput and traceability for long-term monitoring.
• Continued development of isomer-specific standards and reporting conventions will enhance comparability of branched/linear PFAS data across studies and regulatory frameworks.
• Extending robustness testing to additional PFAS classes and emerging compounds will help labs anticipate method limitations and expand target panels.

Conclusion

The study demonstrates that the Xevo TQ Absolute XR coupled with waters_connect for Quantitation can provide robust, long-lived calibration, reliable isomer-specific quantitation, and single-run confirmation of challenging short-chain PFAS using a low-mass fluoride fragment. These capabilities were maintained across demanding, high-throughput sequences and complex matrices for up to five weeks, offering operational advantages for routine environmental PFAS testing by reducing recalibration frequency, supplementary confirmation needs, and consumable costs while maintaining regulatory-quality data.

References

Shah D, Meruva N, Gould D. Solving Analytical Challenges in PFAS Testing: Robust Calibration Data, Low Mass Confirmation and Isomer Quantification. Waters Corporation; 2026. 720009405EN. ©2026 Waters Corporation