Screening of PFAS compounds in wastewater using adsorbable organic fluorine with combustion ion chromatography (CIC)

Importance of the topic

Per- and polyfluoroalkyl substances (PFAS) are widely used synthetic fluorinated chemicals known for their exceptional stability, persistence, and potential bioaccumulation. Their presence in wastewater and other environmental matrices poses significant health and ecological risks, calling for robust screening methods. Combustion ion chromatography (CIC) detecting adsorbable organic fluorine (AOF) offers a matrix-independent approach to estimate total PFAS contamination.

Objectives and overview of the study

This study reports results from the U.S. EPA draft Method 1621 collaborative exercise. Key aims were:

• Validate a screening workflow for AOF in wastewater via CIC.
• Establish method performance metrics: retention times, calibration linearity, detection limits.
• Verify accuracy and precision through method blanks, detection limit tests, and recovery experiments with representative PFAS standards.

Instrumentation used

The analytical setup comprised two major subsystems:

• Ion chromatography: Thermo Scientific Dionex ICS-6000 HPIC system with RFIC, eluent generator, CR-ATC trap, ADRS suppressor, and IonPac AS24 column.
• Combustion-absorption: Nittoseiko AQF-2100H pyrohydrolytic combustion unit with autosampler and offline adsorption for GAC carriers.

Methodology and instrumentation

Wastewater samples (100 mL) were passed through granular activated carbon (GAC) to capture organofluorine. Columns were rinsed with 10 mM NaNO₃ and DI water, dried, then combusted at 950–1 000 °C. Evolved HF was absorbed in DI water and injected (100 µL) onto the IC. A hydroxide gradient (8 mM → 75 mM → 8 mM KOH) at 0.30 mL/min separated fluoride, detected by suppressed conductivity. System blanks, calibration standards (0.5–50 µg/mL F⁻), and quality checks followed EPA Method 1621 protocols.

Main results and discussion

Fluoride eluted at 6.07 ± 0.014 min with a well-resolved peak separated by >3 min from the void. Calibration exhibited linearity over 0.5–50 µg/mL with RSE = 0.77% (1/A² weighting) and r² > 0.999. Initial capability tests yielded recovery of 98.5% ± 4.6% for PFHxS spikes (15 µg F/L). Method blanks averaged 0.69 ng/mL F (σ = 0.17), yielding MDL(b) = 1.23 ng/mL. Spiked MDL standards produced MDL(s) = 2.5 ng/mL. Nine wastewater samples contained 0.53–12.22 ng/mL total fluoride. Recovery tests for PFHxS, PFOS, PFBA, and a PFAS mix at 10 and 30 ng/mL showed 76–117% recovery.

Benefits and practical applications of the method

CIC for AOF screening:

• Eliminates complex matrices via complete combustion.
• Offers low background and high sensitivity (MDL ~2.5 ng/mL).
• Supports high-throughput screening and non-targeted PFAS surveys.
• Integrates seamlessly with automated RFIC for gradient control and reproducibility.

Future trends and opportunities for use

Advancements may include coupling CIC-AOF data with targeted LC-MS/MS profiling, expanding non-targeted PFAS screening in diverse matrices, and further lowering detection limits through improved suppressors and column chemistries. Standardization and broader regulatory adoption of AOF methods will strengthen global PFAS monitoring networks.

Conclusion

The collaborative evaluation of EPA draft Method 1621 demonstrates that combustion ion chromatography effectively quantifies adsorbable organic fluorine in wastewater as a proxy for PFAS contamination. The method delivers robust separation, excellent sensitivity, and accurate recoveries, supporting its use as a rapid screening tool prior to detailed speciation analyses.

References

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