Evaluation of Iodide Chemical Ionization Mass Spectrometry for Gas and Aerosol-Phase per- and polyfluoroalkyl Substances (PFAS) Analysis
Bowers et al.
Environmental Science: Processes Impacts
DOI: 10.1039/D2EM00275B
Together with our partner Aerodyne Research, we continuously support the operation of our mass spectrometers for innovative research. This publication showcases the abilities of the Vocus 2R equipped with the Vocus Aim Reactor to produce precise, real-time molecular data without offline method biases to assess volatile per- and polyfluoroalkyl substances (PFAS).
PFAS are persistent anthropogenic contaminants found in various environments, including water, soil, ice, and human blood. Their presence in atmospheric systems is less understood due to limited measurement techniques for gas and aerosol phases. PFAS emissions occur from manufacturing, use, and disposal of PFAS-containing products, but are often indirectly measured through downstream deposition. Offline measurement methods for PFAS are laborious, prone to contamination, and lack temporal resolution.
Time-of-flight chemical ionization mass spectrometry (TOF-CIMS) offers a promising solution for real-time PFAS monitoring. It enables high-resolution measurements with minimal fragmentation, preserving molecular identities for nontarget analysis. This method is advantageous for identifying new PFAS introduced without disclosure by manufacturers. This study evaluated three sample introduction methods: heated tube for generating gas-phase PFAS from aqueous aerosols, diffusion tube for neutral, volatile PFAS, and Filter Inlet for Gases and Aerosols (FIG-AERO) for sampling aerosol particles and gas-phase PFAS. Successful measurements were obtained for gas-phase fluorotelomer alcohols (FTOHs), gas and aerosol-phase perfluoroalkyl carboxylic acids (PFCAs), and aerosol-phase perfluoroalkyl sulfonic acids and polyfluoroalkyl phosphoric acid diesters (PFSAs and diPAPs). Response factors for these compounds, determined using a FIG-AERO, ranged from 400 to 60,000 ions per nanogram, indicating low detection limits.
Furthermore, understanding PFAS is crucial due to their unique properties stemming from numerous carbon-fluorine bonds. Measuring the binding energy of PFAS-iodide adducts using Vocus technology helps elucidate PFAS properties and improve computational predictions, advancing both analytical chemistry and fundamental physical chemistry knowledge. Detection with iodide-TOF-CIMS depends on the analyte either undergoing proton transfer or forming an adduct with iodide. Voltage scanning experiments and DFT calculations revealed that PFCAs and FTOHs readily form iodide adducts, while PFSAs and diPAPs prefer proton transfer to iodide. Binding energy generally increased with chain length, with PFCAs showing stronger binding than FTOHs. The study suggests that iodide-TOF-CIMS can effectively measure even nonvolatile PFAS, such as PFSAs and diPAPs, in aerosol phases in a semi-continuous online manner.
This study showcases how online measurements using TOFWERK Vocus technology offers precise, real-time molecular data without offline method biases. Previous iodide TOF-CIMS studies measured PFCAs and FTOHs but struggled with PFSAs and diPAPs due to insufficient volatility or lack of iodide-adduct formation. This work suggests PFSAs and diPAPs form ions through proton transfer. Learn more about Vocus capabilities for PFAS detection in the whitepaper, Revolutionizing PFAS Detection in Air: High Sensitivity and Versatility with the Vocus Aim Reactor.
