PhotoTOP: PFAS Precursor Characterization by UV/TiO₂ Photocatalysis

Area of Science:

• Environmental Chemistry
• Analytical Chemistry

Background:

• Per- and polyfluoroalkyl substances (PFAS) are complex and challenging to analyze comprehensively using target methods alone.
• Sum parameters are crucial for characterizing PFAS when reference standards are unavailable or compounds are not amenable to standard analytical techniques.

Purpose of the Study:

• To evaluate photocatalysis (UV/TiO2) as a Total Oxidizable Precursor (TOP) approach, termed PhotoTOP, for characterizing PFAS precursors.
• To convert PFAS precursors into perfluoroalkyl carboxylic acids (PFCAs) for improved analytical detection and characterization.

Main Methods:

• Photocatalysis using UV/TiO2 was employed to oxidize various PFAS precursors.
• Hydroxyl (OH) radicals were monitored to assess reactivity during the photocatalytic process.
• Liquid chromatography-mass spectrometry was used for direct injection analysis after photocatalysis, avoiding sample cleanup.

Main Results:

• Complete conversion of eight different PFAS precursors (diPAPs, FTSAs, FTCAs, N-EtFOSAA, PFOSA) to PFCAs was achieved within 4 hours, even in the presence of matrix components.
• The PhotoTOP method qualitatively predicted the precursor chain length of known and newly identified PFAS.
• Analysis of PFAS-coated paper and technical mixtures showed that the perfluorinated carbon chain length (n) was mostly conserved as PFCAs (n-1).

Conclusions:

• Photocatalysis offers a salt-free, direct injection method for PFAS precursor analysis, simplifying sample preparation.
• The PhotoTOP approach successfully identified and characterized PFAS precursors in complex samples, including indicating the presence of side-chain fluorinated polymers in an unknown fabric sample.