Quadrupole-Resolved All Ions (Q-RAI) Analysis of Select PFAS Chemicals on an Agilent 6546 LC/Q-TOF

Significance of the Topic

Poly- and perfluoroalkyl substances (PFAS) are persistent environmental contaminants with adverse health effects. Their widespread use and stability require sensitive, accurate analytical methods to monitor water quality and comply with regulatory limits such as US EPA Method 533.

Objectives and Overview of the Study

This work evaluates the new Quadrupole-Resolved All Ions (Q-RAI) acquisition mode on the Agilent 6546 LC/Q-TOF for quantitative PFAS analysis according to US EPA Method 533. The study aims to assess sensitivity, reproducibility, linearity, and minimum reporting levels, and to demonstrate retrospective and untargeted analysis capabilities.

Methodology and Instrumentation

Detailed LC and MS conditions were optimized to achieve baseline separation and accurate mass detection of 25 PFAS.

• Liquid chromatography: Agilent 1290 Infinity II with ZORBAX RRHD Eclipse Plus C18 column (3.0 × 50 mm, 1.8 µm) and delay column for background removal. Gradient elution used ammonium acetate in water (20 mM) and methanol at 0.4 mL/min, column temperature 50 °C, 10 µL injection.
• Mass spectrometry: Agilent 6546 LC/Q-TOF in negative electrospray with Q-RAI mode. Isolation windows ranged from 10 to 100 amu with collision energies between 5 and 40 V. Acquisition included low-energy precursor scans (100–1100 m/z at 2 spectra/s) and high-energy fragment scans (25–800 m/z at 11 spectra/s).

Main Results and Discussion

Chromatograms for PFAS acids, sulfonates, and fluorotelomer sulfonates at 1.6 ng/mL showed clear separation and detection of branched isomers.
Quantitation used accurate-mass precursor ions and diagnostic fragment ions with a quadratic 1/x weighted calibration. All compounds achieved calibration R2 > 0.997 and sub-3 ppm mass accuracy.

Reproducibility was demonstrated with RSD values below 11% (n=6) at 6.3 ng/L, outperforming 20% EPA requirements. Reported lowest calibrated minimum reporting levels (LCMRLs) for 24 of 25 compounds were below 5 ng/L, significantly lower than EPA thresholds.

Benefits and Practical Applications of the Method

• High sensitivity and low detection limits for regulatory compliance and environmental monitoring.
• Reliable quantitation with excellent reproducibility and linearity across a wide concentration range.
• Data-independent acquisition enables fragment confirmation and retrospective analysis for emerging PFAS.
• Quadrupole isolation reduces interferences, improving signal-to-noise and confidence in identification.

Future Trends and Applications

The integration of Q-RAI with high-resolution MS is expected to advance untargeted screening of PFAS, facilitating the discovery of novel or previously unregulated compounds. Ongoing improvements in data processing and automation may further enhance throughput and robustness for routine laboratory and field analyses.

Conclusion

The Agilent 6546 LC/Q-TOF with Q-RAI acquisition delivers the sensitivity, reproducibility, and linearity required for US EPA Method 533 PFAS analysis. This approach meets or exceeds regulatory criteria and supports retrospective, untargeted investigations of environmental samples.

References

• Hunt K., Anumol T., Klein C., Pyke J., Hindle R. Quantification of Per- and Polyfluoroalkyl Substances in Drinking Water. Agilent Technologies application note 5994-3648EN, 2021.