Coupling a Gas Chromatograph to a Chemical Ionization Mass Spectrometer for Isomer-resolved Measurements of Airborne PFAS

CHENYANG BI, Yufan Hu, Michael Davern, Joji Sherman, Mitchell Alton, Anita Avery, Nathan Kreisberg, Barbara Turpin, Jason Surratt, John Jayne, Manjula Canagaratna, Aerodyne Research Inc.

     Abstract Number: 561
     Working Group: Chemicals of Emerging Concern in Indoor and Outdoor Aerosol: Sources, Vectors, Reactivity, and Impacts

Abstract
Per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals,” are widely used as water-resistant coatings and surfactants in a range of consumer and industrial products. PFAS represent a broad class of compounds with diverse functional groups and heavily fluorinated carbon chains. Their industrial synthesis often results in mixtures of structural isomers (e.g., linear and branched forms) due to similarities in chain-based structures and the lack of stereochemical constraints during production. These structural isomers can exhibit significant differences in their fate, transport, and toxicity, making isomer-specific analysis essential. While chemical ionization time-of-flight mass spectrometry (CI-TOF-MS) has been used for real-time detection of PFAS in air, it is unable to resolve isomers and is typically calibrated only for the linear-chain isomer of each PFAS class. Consequently, techniques that enable isomer-resolved molecular characterization are essential for understanding the atmospheric fate and transport of individual PFAS isomers. In this study, we couple a thermal desorption aerosol gas chromatograph (TAG), which enables sample preconcentration and isomer separation, with a CI-TOF-MS using iodide as the reagent ion. The TAG-CI-TOF-MS enables the switch between real-time CI-TOF-MS analysis and isomer-resolved gas chromatograph analysis. We demonstrate the instrument performance on separating and preconcentrating analytes by injecting PFAS liquid standards and by measuring oxidation products formed from the reaction of fluorotelomer alcohols (FTOHs) with hydroxyl (OH) radicals in an oxidation flow reactor.