Adsorbable organic fluorine (AOF) – a sum parameter for non-targeted screening of per- and polyfluorinated alkyl substances (PFASs) in waters

Importance of the topic

The growing environmental and health risks posed by per- and polyfluorinated alkyl substances PFAS have made their detection and monitoring in water critical. These stable forever chemicals persist and bioaccumulate, yet traditional targeted analyses cover only a handful of known compounds and require expensive instrumentation and expert operation. A rapid, comprehensive screening parameter is needed to assess total fluorinated burden in waters.

Objectives and overview of the study

This white paper presents adsorbable organic fluorine AOF as a robust sum parameter for non-targeted screening of PFAS and related organofluorine compounds in water. The aim is to compare AOF measurement by combustion ion chromatography CIC with established targeted methods LC-MS/MS, GC-MS/MS and non-targeted precursor assay TOP, demonstrating how AOF can serve as an initial screening step to guide further analysis.

Methodology and applied instrumentation

Sample preparation and analysis workflows include:

• Adsorption of unacidified water samples on activated carbon cartridges to concentrate organofluorine compounds.
• Rinsing cartridges with sodium nitrate solution to remove inorganic fluoride and matrix components.
• Pyrohydrolytic combustion of enriched carbon at 1050 °C in oxygen/argon stream.
• Collection of combustion gases in an absorption solution and determination of fluoride by ion chromatography using an anion exchange column and sequential suppression.

For comparison, targeted analysis methods employ liquid chromatography–tandem mass spectrometry LC-MS/MS or gas chromatography–tandem mass spectrometry GC-MS/MS, while the TOP assay oxidizes precursors into measurable PFAS.

Applied instrumentation

The core instrumentation comprises a combustion ion chromatograph CIC system equipped with a Metrosep A Supp 5-250/4.0 column, high-temperature combustion module, and sequential suppressor. Complementary targeted analyses utilize LC-MS/MS and GC-MS/MS platforms, and high-resolution mass spectrometry HRMS for the TOP assay.

Main results and discussion

AOF determination by CIC achieved a limit of detection of 0.5 µg/L fluoride, reliably measuring total adsorbable fluorine including known and unknown PFAS, precursors, isomers, and other fluorinated contaminants. Compared with TOF (total organic fluorine) via CIC, AOF provides higher sensitivity through preconcentration on activated carbon. Elevated AOF values effectively trigger follow-up targeted analysis when individual PFAS levels require confirmation. The method is faster and more robust than extensive LC-MS/MS panels and avoids the complexity of TOP assays.

Benefits and practical applications

Using AOF as a screening parameter offers:

• Broad coverage of known and emerging PFAS and other fluorinated compounds.
• Simple sample preparation and reduced analysis time.
• Lower requirements for specialized reference standards and blank materials.
• Enhanced sensitivity compared to TF and TOF measurements.
• Cost-effective preliminary assessment before targeted assays.

This approach supports routine monitoring at water treatment plants, wastewater facilities, and environmental laboratories to track organofluorine contamination.

Future trends and opportunities

Ongoing developments include integration of AOF with advanced non-targeted HRMS workflows for compound identification, standardized interlaboratory protocols for sum parameters, lower detection limits through optimized adsorption materials, and expansion of AOF application to solid matrices and sediments. Combined use of AOF, EOF (extractable organic fluorine), and TOP assays will enhance understanding of PFAS fate and transformation.

Conclusion

Adsorbable organic fluorine measured by combustion ion chromatography provides an efficient, sensitive, and comprehensive screening tool for the total burden of organofluorine compounds in water. As a sum parameter, AOF complements targeted and precursor assays, guiding detailed PFAS analyses and supporting regulatory compliance and environmental protection efforts.

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