Stable Carbon Isotope Analysis of PFOA and PFOS Using Orbitrap Mass Spectrometry

High Resolution Image Download MS PowerPoint Slide Compound-specific isotope analysis (CSIA) is a powerful tool for pollutant source apportionment. However, conventional isotope ratio mass spectrometry (IRMS) is limited for nonvolatile compounds like perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Here, we demonstrated high-resolution Orbitrap mass spectrometry for δ 13 C analysis of these compounds. This technique enables direct isotopologue detection without combustion, providing nM-level sensitivity and molecular structure preservation. δ 13 C values for PFOA and PFOS reagents agreed well with those from elemental analyzer IRMS (EA-IRMS), with deviations within ±2.0‰ across resolution settings (17,500–140,000). Higher automatic gain control (AGC) targets improved precision; the optimal setting (5 × 10 6 ) yielded standard deviations below 1.2‰. Seven PFOA and two PFOS standards, each obtained from different commercial suppliers, were analyzed. The δ 13 C values measured by Orbitrap showed good agreement with EA-IRMS. In addition, spiked experiments using three different river water samples demonstrated that reliable δ 13 C measurements of PFOA and PFOS can be achieved in realistic aqueous environmental matrices. This approach expands the applicability of CSIA to nonvolatile PFAS and provides a new isotopic perspective for investigating their environmental sources and fate.