AOF by combustion IC – non-targeted complemental determination of PFAS in aqueous samples

Importance of the topic

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants widely used in consumer products and industrial applications. Their resistance to degradation and potential health effects have raised regulatory concerns. Conventional targeted methods cover only a subset of PFAS, leaving many fluorinated precursors undetected. A sum parameter approach for adsorbable organically bound fluorine (AOF) via combustion ion chromatography (CIC) offers a complementary tool to assess total fluorinated organic load in water.

Objectives and study overview

This work aimed to develop and validate an automated CIC method for non-targeted determination of PFAS and related fluorinated organics in aqueous samples. Researchers optimized sample adsorption on activated carbon, automated combustion of sorbent and analytes, and IC detection of released fluoride. Comparative data with established LC-MS/MS techniques were obtained to demonstrate the method’s broad coverage and practicality.

Methodology and used instrumentation

The protocol combines automated solid-phase extraction and CIC.

• Sample adsorption: AutoAD SPE module with AOXpack Premium activated carbon cartridges.
• Combustion system: Mitsubishi AQF-2100H furnace (950–1000 °C) with argon/oxygen carrier gases and water quench (hydropyrolysis) to minimize matrix interactions.
• Detection: Thermo Scientific Dionex ICS-2100 RFIC system with continuous KOH gradient elution, AERS 500 suppressor in constant current mode, and suppressed conductivity detection.
• Software: Chromeleon CDS v7.2.9 and Mitsubishi NSX-2100 v2.1.6.0.

Main results and discussion

• Calibration: Fluoride response linear from 2 to 500 µg/L (r2 > 0.9999), LOD = 1.3 µg/L, LOQ = 2 µg/L.
• Interference: Inorganic fluoride below 0.2 mg/L had no effect on AOF; routine rinsing removed matrix fluoride.
• Recoveries: Model PFAS and commercial products showed recoveries from 16% (small fluorosulfonyl fluorides) to 121% (firefighting foam concentrates), with C4–C8 acids achieving >80%.
• Environmental samples: PFBS spike recoveries were 92–109% in surface water and 85–102% in wastewater. 4-fluorobenzoic acid recoveries ranged 82–127%.
• Occurrence data: Surface water AOF 4.5–10.2 µg/L (max 24.5 µg/L); groundwater mostly 500 µg/L, far exceeding targeted PFAS levels (<5% of AOF), indicating significant non-target organofluorine.

Benefits and practical applications

• Broad screening tool: Captures known and unknown PFAS precursors and other fluorinated organics in one workflow.
• Cost efficiency: Reduces need for extensive LC-MS/MS analysis by flagging high-AOF samples for targeted follow-up.
• Regulatory support: Aligns with emerging standard methods for adsorbable organofluorine monitoring.

Future trends and possibilities

• Standardization: Finalization of DIN protocols for AOF/CIC analysis.
• Advanced sorbents: Improved carbon materials for broader analyte retention.
• Hyphenation: Combining CIC with high-resolution mass spectrometry for event-driven non-target profiling.
• Extension to other halogenated organics, such as brominated and chlorinated compounds.

Conclusion

Automated AOF determination by CIC is a robust, sensitive, and non-targeted approach for assessing fluorinated organic contaminants in environmental waters. It complements targeted LC-MS/MS methods by revealing the total organofluorine burden, guiding regulatory monitoring and source identification.

Reference

1. von Abercron E et al. Sci Total Environ. 2019;673:381–391.
2. DIN 38407-42. German standard methods for PFAS by HPLC-MS/MS; Beuth Verlag, 2011.
3. ISO 9562:2004. Water quality – AOX determination; Beuth Verlag, 2004.
4. ISO 10304-1:2007. Dissolved anions by ion chromatography; Beuth Verlag, 2007.
5. Wagner A et al. J Chromatogr A. 2013;1295:82–89.