Analysis of Perfluorooctanesulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) in Tap Water Using a Triple Quadrupole LC/MS/MS

Significance of PFOS/PFOA Analysis in Tap Water

Persistent organic fluorinated compounds such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) accumulate in the environment and pose health risks. Regulatory agencies have set a combined target limit of 50 ng/L in drinking water, necessitating sensitive and reliable analytical methods for routine monitoring.

Objectives and Study Overview

The study aims to validate a quantitative LC-MS/MS method using a triple quadrupole mass spectrometer (LCMS-8050) for simultaneous determination of PFOS and PFOA in tap water. Key goals include achieving detection limits well below the regulatory target, ensuring method accuracy, precision, and demonstrating applicability to real water samples.

Methodology and Instrumentation

Sample Preparation:

• Volume: 500 mL tap water
• Internal standards: 13C8-PFOS and 13C8-PFOA spiked at 10 ng/L
• SPE: Anion-exchange cartridge, conditioned and eluted with ammonia/methanol mixtures
• Concentration: Nitrogen blow-down to 0.5 mL and reconstitution in methanol (1000× concentration)

Chromatography and Detection:

• Instrument: Shimadzu LCMS-8050 triple quadrupole LC-MS/MS
• Column: Shim-pack GIST C18-AQ HP (150 × 2.1 mm, 3 µm)
• Mobile phases: 10 mmol/L ammonium acetate (A) and acetonitrile (B)
• Gradient: 25 % B to 100 % B over 30 min, then re-equilibration
• Flow rate: 0.2 mL/min; column temperature: 40 °C; injection: 5 µL
• Ionization: ESI negative mode, MRM transitions m/z 498.95 > 79.95 for PFOS and m/z 413.05 > 168.95 for PFOA

Main Results and Discussion

Calibration and Sensitivity:

• Linear range: 1–20 µg/L, R2 > 0.999 for both analytes
• Detection achievable at 1 ng/L after 1000× concentration, ensuring compliance margin well below the 50 ng/L limit

Recovery and Precision:

• Spike-and-recovery in tap water (5 ng/L): PFOS recovery 104 % (RSD 1.2 %), PFOA recovery 79 % (RSD 3.4 %)
• Accuracy of control samples (5 µg/L): PFOS 101 %, PFOA 99 %

Benefits and Practical Application

The validated method offers:

• High sensitivity to detect PFOS/PFOA at sub-ng/L levels
• Robust quantitation with excellent linearity and reproducibility
• Streamlined workflow compatible with routine water quality monitoring in research and QA/QC laboratories

Future Trends and Potential Applications

Emerging analytical needs include broadening the target list to other per‐ and polyfluoroalkyl substances (PFAS), automation of SPE steps, and coupling high-resolution mass spectrometry for non-target screening. Integration with online SPE-LC systems and miniaturized extraction platforms could further enhance throughput and minimize solvent usage.

Conclusion

The LCMS-8050 triple quadrupole LC-MS/MS method meets regulatory requirements for PFOS and PFOA in tap water, delivering reliable quantification down to 1 ng/L. The approach is suitable for routine water quality surveillance and supports public health protection efforts.

References

• Shimadzu Corporation. Application Note No. C224. First Edition: Aug. 2020.