Compound-specific carbon isotope analysis of perfluorocarboxylic acids (PFCAs) by gas chromatography-isotope ratio mass spectrometry

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals widely used for their thermal and chemical resistance but are now of major environmental concern due to their persistence, bioaccumulation, and adverse health effects. Regulatory actions have been implemented globally, yet efforts to identify sources and degradation processes remain hindered by analytical limitations. Compound-Specific Isotope Analysis (CSIA) offers a promising approach for tracing PFAS sources and assessing their environmental transformation, but its application has been limited by the lack of suitable methods. This study presents the development and validation of a CSIA method for selected perfluorocarboxylic acids (PFCAs) and heptadecafluorooctane sulfonic acid (PFOS) using gas chromatography-Isotope Ratio Mass Spectrometry (GC-C-IRMS). An isobutyl-derivatization procedure was optimized to enhance compatibility with GC analysis, enabling successful isotope ratio measurements for perfluoroheptanoic acid (PFHpA), pentadecafluorooctanoic acid (PFOA), and nonadecafluorodecanoic acid (PFDA), with precision below ±0.5 ‰. In contrast, heptadecafluorooctane sulfonic acid (PFOS) could not be analyzed. Preliminary Elemental Analysis-IRMS (EA-IRMS) of standards from multiple suppliers revealed significant isotopic variability (up to 10 ‰), supporting the feasibility of isotopic fingerprinting for source attribution. Solid-phase microextraction (SPME) was employed for sample preparation, minimizing chromatographic interference. The method was successfully tested on real water samples spiked with PFCAs, demonstrating its potential for tracing PFCAs contamination in real-world contexts. This work lays the foundation for broader application of CSIA to PFCAs, providing a novel tool for environmental forensics and improved risk assessment.