Analysis of AOF (Adsorbable Organic Fluorine) According EPA Method 1621

Importance of the Topic

This application addresses the growing need for reliable screening of adsorbable organic fluorine (AOF) in water. Per- and polyfluoroalkyl substances (PFAS) and other fluorinated organic compounds pose environmental and health risks due to their persistence and bioaccumulation. AOF analysis based on EPA Method 1621 provides a comprehensive measure of total organic fluorine load, supporting water quality monitoring, regulatory compliance, and risk assessment.

Aims and Overview of the Study

The study demonstrates the integration of combustion ion chromatography (CIC) for AOF determination by applying EPA Method 1621. It evaluates initial precision and recovery (IPR) and method detection limits (MDL) using perfluorohexane sulfonic acid (PFHxS) as the spiking compound. The goal is to confirm method performance against regulatory criteria and to showcase automated sample processing.

Methodology and Instrumentation

The procedure involves five main steps:

1. Sample loading onto a granular activated carbon (GAC) column via TXA-04 absorption unit to capture organic fluorine.
2. Rinsing the GAC column to remove inorganic fluoride.
3. Transfer of the GAC to a ceramic combustion boat.
4. High-temperature combustion (1000–1100 °C) of the sample to convert organic fluorine to hydrogen fluoride.
5. Collection of combustion gases in an absorption solution, followed by fluoride analysis by ion chromatography.

Instrumentation Used

• AQF-5000H combustion unit (Nittoseiko Analytech) with ceramic sample boat and quartz-ceramic pyrolysis tube.
• HIC-ESP ion chromatograph (Shimadzu) equipped with an electrodialytic suppressor (ICDS-40A).
• Shim-pack IC-SA2 anion exchange column (250 mm × 4.0 mm, 9 µm).
• Gas flows: oxygen 400 mL/min, argon 200 mL/min, humidified argon 100 mL/min.
• Absorption solution: ultrapure water, final volume 11.3 mL.

Main Results and Discussion

A six-point combustion calibration curve (1.8–442.5 µg/L fluoride) was fitted with a quadratic equation, with measured concentrations within 80–120% of nominal values. Method blanks yielded less than 0.60 µg/L fluoride (criteria < 4.0 µg/L). IPR tests at 25 µg/L PFHxS showed an average recovery of 95.5% and RSD of 2.4% (criteria: recovery 80–120%, RSD < 20%). MDL calculations gave MDLb = 0.97 µg/L and MDLs = 1.27 µg/L, establishing an MDL of 1.27 µg/L in compliance with EPA Method 1621.

Benefits and Practical Applications of the Method

The CIC approach provides:

• Comprehensive screening for all adsorbable organic fluorine, including non-targeted PFAS and fluorinated compounds.
• Automation of sample combustion and ion chromatography for high throughput and reduced operator intervention.
• Simplicity and robustness suitable for routine monitoring in environmental and industrial laboratories.

Future Trends and Applications

Advances may include coupling AOF screening with mass spectrometry for compound identification, miniaturized CIC modules for on-site monitoring, expanded application to complex matrices (soil, biota), and integration into green analytical workflows to minimize reagent use and waste.

Conclusion

The combination of the AQF-5000H combustion unit and the HIC-ESP ion chromatograph delivers a validated, automated solution for AOF screening under EPA Method 1621. The method meets precision, recovery, and detection limit requirements, offering a powerful tool for comprehensive fluorine analysis in water.

Reference

• USEPA Method 1621: Screening Method for the Determination of Adsorbable Organic Fluorine in Aqueous Matrices by Combustion Ion Chromatography.
• 40 CFR Part 136, Appendix B: Definition and Procedure for the Determination of the Method Detection Limit—Revision 2.