Stable carbon isotope analysis of fluorinated organic compounds using infrared spectrometer coupled to gas chromatography

Abstract

Compound-specific isotope analysis (CSIA) is a powerful tool for tracing the sources and transformation processes of organic pollutants. With the rising concern on fluorinated organic compounds, there is a pressing need to develop reliable CSIA methods for determining their carbon isotopic compositions. This study developed a gas chromatography–isotope ratio infrared spectrometer (GC-IRIS) method for carbon CSIA of perfluorinated carboxylic acids and ethers. The δ¹³C signatures determined by GC-IRIS were −26.1 ± 0.3‰ for heptafluorobutyric acid, −30.1 ± 0.3‰ for perfluoro-2-butyltetrahydrofuran, −30.2 ± 0.3‰ for trifluoroacetic acid, −41.0 ± 0.2‰ for perfluoropentanoic acid, −45.3 ± 0.2‰ for perfluorobutyl methyl ether, and −55.9 ± 0.4‰ for perfluoropropyl vinyl ether, respectively. Cross-validation using elemental analysis–isotope ratio mass spectrometry (EA-IRMS) confirmed consistency between the two methods, showing good agreement in the δ¹³C values, supporting the reliability of the GC-IRIS method. The method was further applied to resolve carbon isotope fractionation during volatilization of perfluorobutyl methyl ether and perfluoro-2-butyltetrahydrofuran, both exhibiting inverse carbon isotope effects. This work reports a novel and robust GC-IRIS method for carbon CSIA of fluorinated compounds, highlighting the potential for characterizing isotopic signatures and environmental behaviors of different fluorinated organic compounds.