Infrared Matrix-Assisted Laser Desorption Electrospray Ionization (IR-MALDESI) Mass Spectrometry Imaging of Per- and Polyfluoroalkyl Substances (PFAS) in Stabilized Soil Cores.

Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) was coupled with high-resolution accurate-mass-mass spectrometry (HRAM-MS) to image perfluoroalkyl and polyfluoroalkyl substances (PFAS) in stabilized soil cores. Previous field-scale research demonstrated a substantial decrease in the leachability of PFAS following the application of in situ stabilization and solidification (S/S) in an aqueous film-forming foam (AFFF) source zone. While this previous study empirically confirmed the effectiveness of S/S, there was no definitive identification of the operative retention mechanisms. Therefore, the objective of this follow-on study was to (1) develop a high-resolution mass spectrometry-based imaging technique for PFAS on stabilized and background control soil cores and (2) determine if chemical characteristics of the amendments were associated spatially with the PFAS distribution within the soil cores at a micrometer scale. Intact frozen soil cores were imaged in negative ion mode, targeted and suspect screening analyses were conducted, features were identified using suspect lists, and analytes were presented as raw abundances matched against several databases. IR-MALDESI imaging results confirmed the colocation of PFOS and PFHxS with non-PFAS chemical features (e.g., mono- and diglycerides) associated with treatments including amendments, which suggests chemical fixation as a mechanism of stabilization for PFAS in stabilized soil cores.