Feasibility study of superoxide chemical ionization mass spectrometry (O2− CIMS) for real-time gas-phase measurements of per- and polyfluoroalkyl substances (PFAS)

Abstract

Per- and polyfluoroalkyl substances (PFAS) are highly persistent pollutants with known adverse impacts on environmental and public health. Traditional gas-phase PFAS detection approaches often involve labor-intensive sample collection and preparation, while offering low temporal resolution. Alternatively, chemical ionization mass spectrometry (CIMS) allows for real-time airborne PFAS detection at sub-pptv sensitivity. While reagent ion generation often requires hazardous chemicals (e.g., nitric acid, methyl iodide (I⁻), and acetic anhydride), superoxide (O₂⁻) CIMS provides a safer alternative and is better suited for mobile platforms where ventilation, space, and weight are constrained. O₂⁻ CIMS has five main reagent ions (i.e., O₂⁻, (H₂O)O₂⁻, CO₃⁻, (CO₂)O₂⁻, and CO₂(H₂O)O₂⁻) and low-background mass spectra above m/z 200. Thus, it is well suited to the relatively high molecular weights of airborne PFAS. Mass calibration was performed with a 5 : 1 fluorotelomer alcohol (FTOH) permeation tube. Ionization was found to occur mainly through deprotonation or adduct formation. Calibrations for fourteen environmentally- and industrially-relevant PFAS compounds are presented, including FTOHs, fluorotelomer diols, fluorinated sulfonamides, epoxides, and glycol ethers. While perfluoroalkyl carboxylic acids (PFCAs) were not detected, O₂⁻ CIMS offered higher sensitivity and lower detection/quantification limits than I⁻ CIMS for FTOHs; however, it remains a complementary PFAS measurement technique to I⁻ CIMS. Moreover, it yielded distinct fingerprint signals for FTOHs, confirming compound identification. This study demonstrates the utility of O₂⁻ CIMS for real-time airborne PFAS analysis in commonly encountered environments by capturing 6 : 2 FTOH gaseous emissions from fast-food packaging at room temperature, underscoring its strong promise for future development and applications.