Trace-level determination of perfluorinated compounds in water by suppressed ion chromatography with inline matrix elimination

Significance of the Topic

This study addresses the need for rapid, sensitive and cost-effective analysis of perfluorinated alkyl substances (PFAS) in water, focusing on perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). These persistent environmental contaminants pose health risks and require reliable monitoring at trace levels. The presented ion chromatography (IC) method with suppressed conductivity detection and inline matrix elimination offers an accessible alternative to more expensive LC-MS/MS approaches.

Objectives and Study Overview

The primary goal was to develop and validate a direct-injection IC method for quantifying PFOA and PFOS in drinking water. Key aims included establishing linear calibration ranges, assessing precision, and evaluating matrix effects from common anions and alkaline-earth cations. For samples with elevated divalent cation content, an inline cation removal step was integrated to ensure accurate PFAS recovery.

Instrumental Setup

• 850 Professional IC Anion with suppressed conductivity detector and MCS – Prep 3.
• 858 Professional Sample Processor equipped with Metrohm Inline Cation Removal module.
• ProntoSil 120-5-C18 AQ reversed-phase column, thermostated at 35 °C.

Methodology

The separation employed isocratic elution using a mobile phase of 20 mmol/L boric acid, 4.0 mmol/L NaOH (pH 8) and 38% acetonitrile at a flow rate of 1.0 mL/min. Samples (1000 µL loop) were directly injected for low-salt matrices. For high Ca2+ or Mg2+ levels (>10 mg/L), the Metrohm Inline Cation Removal exchanged divalent cations for sodium in-line prior to column transfer.

Main Results and Discussion

• Calibration: PFOA (2–50 µg/L) and PFOS (10–250 µg/L) yielded R² values of 0.99990 and 0.99910, respectively.
• Precision: Relative standard deviations were below 1.8% for PFOA and 5.7% for PFOS.
• Anion matrix effects: Chloride and sulfate up to 200 mg/L did not significantly affect PFAS quantification.
• Cation interference: Mg2+/Ca2+ above 10 mg/L reduced PFOS recovery; inline cation removal improved PFAS recoveries from 90–115% to 93–107% in samples containing up to 350 mg/L divalent cations.

Benefits and Practical Applications of the Method

This IC approach offers:

• Direct injection without extensive sample preparation for low-salt waters.
• Effective inline removal of divalent cations for complex matrices (tap, lake, river, sludge water).
• High sensitivity and reproducibility at low µg/L levels.
• Lower operating and capital costs compared to LC-MS/MS workflows.

Future Trends and Possibilities

Potential developments include expanding the method to additional PFAS homologues, coupling suppressed IC with mass spectrometry for confirmatory analysis, and integrating automated inline cleanup modules for fully unattended PFAS monitoring. Adoption in routine regulatory and industrial water quality testing can be expected.

Conclusion

The described suppressed ion chromatography method with inline cation removal provides a robust, accurate and economical tool for trace-level determination of PFOA and PFOS in diverse water matrices, supporting environmental surveillance and compliance.

References

Gandhi J., Subramanian N.H., "Trace-level determination of perfluorinated compounds in water by suppressed ion chromatography with inline matrix elimination", Metrohm poster.