Analysis of Adsorbable Organic Fluorine (AOF) by Combustion Ion Chromatography (CIC)

Significance of the Topic

The accurate assessment of adsorbable organic fluorine (AOF) in water is critical for screening per- and polyfluoroalkyl substances (PFAS) and other fluorinated compounds that pose environmental and health risks.

Objectives and Overview of the Study

This study demonstrates an analytical workflow based on the EPA Draft Method 1621 for AOF determination using combustion ion chromatography (CIC). It aims to:

• Validate the initial precision and recovery (IPR) of the method with perfluorohexane sulfonic acid (PFHxS) spike tests.
• Establish calibration performance for fluoride detection.
• Apply the method to real river water samples to confirm detection capability at trace levels.

Methodology and Instrumentation

Sample preparation and analysis follow these key steps:

1. Pass the water sample through a TXA-04 unit containing granular activated carbon (GAC) to adsorb organic fluorine.
2. Transfer the GAC to a ceramic combustion boat and combust at 1000 – 1100 °C in the AQF-2100H unit under controlled oxygen and argon flows.
3. Capture combustion gases in reagent water to convert bound fluorine into fluoride ions.
4. Analyze the absorption solution by ion chromatography using a Shim-pack IC-SA2 column and ICDSTM-40A suppressor for conductivity detection.
5. Generate a five-point calibration curve (0.01–0.5 mg/L fluoride) to ensure linearity (r ≥ 0.999).

Used Instrumentation

• Nittoseiko Analytech AQF-2100H combustion unit with ceramic boat and quartz/ceramic pyrolysis tube
• Shimadzu HIC-ESP ion chromatograph equipped with ICDSTM-40A suppressor
• TXA-04 adsorption unit for GAC sample preparation
• Shim-pack IC-SA2 anion-exchange column (4.0 mm×250 mm, 9 µm)

Main Results and Discussion

Calibration exhibited excellent linearity for all analytes. In the IPR test (19.5 µg/L spike of PFHxS):

• Average recovery: 93.0 % (acceptance 70–130 %)
• Relative standard deviation: 8.3 % (acceptance < 20 %)
• Method blank: 1.6 µg/L (acceptance < 3.0 µg/L)

Analysis of a 100 mL river water sample yielded an AOF concentration of 1.6 µg/L after blank correction, confirming the method’s capability to detect fluorine at parts-per-billion levels.

Benefits and Practical Applications

• Simplified, full‐automation workflow from sample combustion to ion chromatography analysis.
• Broad capture of both PFAS and non‐PFAS organofluorines without compound‐specific targets.
• High sensitivity and reproducibility suitable for routine environmental monitoring, QA/QC, and regulatory screening.

Future Trends and Potential Applications

Emerging opportunities include:

• Integration with high‐throughput autosamplers and online data processing.
• Extension of AOF analysis to complex matrices such as soils, sediments, and biota.
• Coupling CIC with mass spectrometry for compound identification and speciation.
• Standardization of AOF as a regulatory parameter in drinking and wastewater guidelines.

Conclusion

The CIC method following EPA Draft Method 1621 delivers robust, sensitive, and automated AOF screening. It meets stringent precision and recovery criteria and effectively quantifies total adsorbable fluorine in environmental water samples at trace levels.

References

• EPA Draft Method 1621: Screening Method for the Determination of Adsorbable Organic Fluorine in Aqueous Matrices by Combustion Ion Chromatography