EVALUATION OF DESI MOUNTED ON Q-TOF AND TQ MASS SPECTROMETERS TO IMAGE PFAS COMPOUNDS IN DIFFERENT MATRICES

Importance of the topic

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent environmental contaminants that bioaccumulate in animals, humans and ecosystems. Their detection and localization within solid matrices such as tissues or plants remains challenging with conventional LC-MS/MS workflows that require extensive sample preparation and lack spatial information. Mass spectrometry imaging (MSI) via desorption electrospray ionization (DESI) offers a direct, label-free approach to map PFAS distributions at high spatial resolution, supporting environmental monitoring, toxicological studies and quality control.

Objectives and Study Overview

This study aimed to evaluate the performance of a DESI source coupled to three mass spectrometry platforms—a high-sensitivity tandem quadrupole (Xevo TQ Absolute MS in multiple reaction monitoring, MRM), a high-resolution multi-reflecting Q-Tof (SELECT SERIES MRT) and a cyclic IMS Q-Tof (SELECT SERIES Cyclic IMS)—for achieving low limits of detection and spatial mapping of PFAS in different matrices. Spotted dilution series on porcine liver sections and PFAS-contaminated lentil roots and seeds served as model systems.

Methodology and Instrumentation

Sample Preparation and Analysis Conditions

• PFAS mixture containing commonly studied analytes (PFHxS, PFOS, PFOA, PFNA, PFDA, FBSA, FOSA, etc.) was diluted to 1–500 ng/mL in 50:50 MeOH/H₂O.
• One microliter spots were applied to 10-µm porcine liver cryosections; lentils were germinated in PFAS solution and cryosectioned at 100 µm.
• DESI-XS source parameters: 2 µL/min solvent flow (95:5 MeOH:H₂O with Leu-enkephalin), 10 psi N₂, capillary voltage 0.55–0.75 kV, pixel size 50–100 µm, acquisition speed 1–5 Hz.

Instrumentation Used

• Xevo TQ Absolute MS (tandem quadrupole, MRM mode)
• SELECT SERIES MRT (multi-reflecting Q-Tof, full-scan TOF-MS)
• SELECT SERIES Cyclic IMS (cyclic IMS Q-Tof, TOF-MS and IMS mode)
• High-performance sprayer (HPS) for enhanced DESI sensitivity and robustness

Main Results and Discussion

• LOD Assessment: The Xevo TQ MRM workflow detected 77% of PFAS at ≤10 ng/mL on tissue; full-scan TOF setups achieved 61% (MRT) and 54% (Cyclic IMS) at the same level.
• Ion Mobility Separation: IMS dimension separated PFAS from background ions, improving signal-to-noise ratios and resolving multiple gas-phase conformers of compounds such as N-EtFOSAA.
• Spatial Imaging of Plants: Targeted MSI of lentil root and seed revealed distinct accumulation patterns for PFHxS and FHxSA, demonstrating the method’s capacity to localize PFAS in biological samples.

Benefits and Practical Applications

• Eliminates laborious extraction and cleanup steps, preserving spatial context of PFAS distribution.
• Enables rapid screening and mapping of multiple PFAS in tissues, food matrices and environmental samples.
• High specificity and sensitivity via MRM on TQ systems facilitate quantitation at low nanogram levels.
• IMS separation adds selectivity against complex chemical backgrounds.

Future Trends and Potential Applications

• Integration of advanced ion mobility techniques for isomer differentiation and structural elucidation.
• Expansion to other classes of emerging contaminants (e.g., microplastics, pesticides).
• Automation and high-throughput workflows for routine environmental and food safety analyses.
• Coupling with quantitative imaging software for absolute concentration mapping.

Conclusion

A DESI-MSI approach mounted on both Q-Tof and tandem quadrupole platforms enables sensitive detection and precise spatial mapping of PFAS in complex matrices. The Xevo TQ in MRM mode offers the lowest detection limits, while ion mobility on the Cyclic IMS Q-Tof further enhances selectivity and conformational insights. This workflow holds significant promise for environmental monitoring, toxicological research and industrial quality control.