Significance of the topic
Volatile per- and polyfluoroalkyl substances (PFAS) are a subset of persistent “forever chemicals” that may volatilize from treated consumer materials and contribute to indoor air contamination and human exposure. Because many volatile PFAS and their transformation products are not included in routine targeted methods, untargeted, high-confidence screening approaches are needed to detect known, emerging, and previously uncharacterized species. Combining thermal desorption (TD) preconcentration with high-resolution accurate-mass (HRAM) gas chromatography–mass spectrometry (GC–MS) and advanced data workflows enables comprehensive monitoring of volatile PFAS in complex indoor air matrices, improving exposure assessment and source identification.
Objectives and study overview
This study demonstrates an end-to-end untargeted workflow based on thermal desorption coupled to an Orbitrap GC high-resolution mass spectrometer (Orbitrap Exploris GC) for screening volatile PFAS in indoor air. The goals were to (1) establish a TD-GC-HRAM method with sensitive detection and separation of a broad PFAS range, (2) apply software-driven untargeted data processing for confident identification, and (3) evaluate indoor air from different environments (carpeted, non-carpeted, cleaning-storage areas) to illustrate method performance and relative PFAS occurrence.
Methods and methodology
Sampling and sample preparation:
- Indoor air sampled onto TD-compatible sorbent tubes using pumped sampling; typical sample volume reported was 35 L per sample.
- PFAS multi-component standard prepared in methanol and spiked onto sorbent tubes to support method development, chromatographic separation checks, and identification confidence.
Analytical workflow:
- Thermal desorption (TD) used to thermally release and preconcentrate volatiles directly to the GC inlet, minimizing solvent use and extensive sample prep.
- GC separation performed on a TraceGOLD TG-200MS column (as used for presented EIC examples).
- High-resolution mass spectrometry acquisition on an Orbitrap Exploris GC with full-scan HRAM acquisition using electron ionization (EI) and chemical ionization (CI). Variable electron voltage (VeV) was referenced as an approach to enhance sensitivity for volatile PFAS.
- Data-dependent MS/MS (PCI ddMS2) acquisition implemented to confirm molecular ions and obtain diagnostic fragments with high mass accuracy (example: 6:2 FTOH confirmation by PCI ddMS2, accurate m/z 364.0369, and FISh coverage).
Data processing and identification strategy:
- Automated peak detection, deconvolution, and library matching performed with Thermo Scientific Compound Discoverer software, supported by Chromeleon CDS and FreeStyle for data handling.
- Identification filters included HRAM mass accuracy, isotopic and fluorine-based filtering, spectral library matches, fragmentation matching, FISh scoring, and in silico fragmentation tools for tentative IDs of compounds absent from libraries.
Used instrumentation
- Thermal desorption system with TD-compatible sorbent tubes.
- Gas chromatograph with TraceGOLD TG-200MS column.
- Thermo Scientific Orbitrap Exploris GC high-resolution mass spectrometer (EI and CI modes; PCI ddMS2).
- Software: Thermo Scientific Compound Discoverer, Chromeleon CDS, FreeStyle.
Main results and discussion
The TD-GC-HRAM workflow successfully detected a range of volatile PFAS in indoor air samples and standard mixtures. Key findings include:
- Sensitive separation and detection: Extracted ion chromatograms of the PFAS standard mix (5 ng on column) demonstrated effective chromatographic separation and high-resolution spectral quality (example shown for 9ME-8:2 FTOH HRAM spectrum).
- Robust identification in complex matrices: High-resolution full-scan data combined with deconvolution and fluorine-based filtering enabled confident identification even for low-intensity peaks and co-eluting components.
- MS/MS confirmation: PCI ddMS2 provided diagnostic fragment ions and high mass accuracy (e.g., 6:2 FTOH confirmed at m/z 364.0369 with supporting FISh coverage), increasing assignment confidence beyond EI spectra alone.
- Environmental distribution: Relative PFAS levels were highest in carpeted and cleaning-storage areas, indicating indoor sources associated with flooring and cleaning product storage/use.
- Data mining and differential analysis: Automated workflows allowed group comparisons (boxplot/differential analysis), library matching, and exploratory searches against online resources (e.g., ChemSpider) for unknowns.
Collectively, the results show that TD coupled to Orbitrap GC-HRAM, together with modern data-processing workflows, extends detection capability to volatile and semi-volatile PFAS classes that are challenging for targeted assays and supports discovery of emerging or previously uncharacterized fluorinated compounds.
Benefits and practical applications of the method
- Comprehensive untargeted surveillance: Detects known and novel volatile PFAS without prior selection of target analytes, useful for screening, source apportionment, and hypothesis generation.
- High confidence identifications: HRAM acquisition and MS/MS confirmation reduce false positives from co-elution and matrix interferences.
- Minimal sample preparation: TD preconcentration of sorbent tube samples reduces handling, sample loss, and solvent use versus solvent-based extraction workflows.
- Applicable to indoor air quality assessment: Enables laboratories and environmental practitioners to detect PFAS hotspots (e.g., carpets, cleaning storage) and to prioritize follow-up monitoring or mitigation.
- Extensible to unknowns: In silico fragmentation and database searching broaden the ability to tentatively identify PFAS absent from spectral libraries.
Future trends and opportunities
- Expansion of HRAM spectral libraries and fluorine-specific filters will improve the rate of confident identifications for emerging PFAS species.
- Integration of in silico prediction, machine learning and automated scoring will accelerate annotation of unknowns and reduce analyst time.
- Quantitative extensions: Combining TD-GC-HRAM screening with targeted quantitative workflows (including approaches such as SPME Arrow referenced in existing application notes) will support exposure and risk assessment with concentration data.
- Sampling innovation: Optimization of sorbent materials, larger-volume or passive sampling strategies, and standardized protocols will increase comparability across studies.
- Regulatory and monitoring uptake: As untargeted HRAM workflows mature, they can inform regulatory monitoring, product stewardship, and indoor air quality guidelines for PFAS.
Conclusions
The presented TD-GC-HRAM workflow on an Orbitrap Exploris GC platform provides a sensitive and flexible approach for untargeted screening of volatile PFAS in indoor air. Thermal desorption simplifies sample handling while HRAM full-scan and data-dependent MS/MS acquisition deliver high-confidence identifications in complex matrices. Advanced software workflows enable deconvolution, fluorine-based filtering, library matching, and in silico support for unknowns. The method effectively discriminated PFAS occurrence across indoor environments, with elevated signals linked to carpeted and cleaning-storage areas, and offers a practical route for laboratories to implement discovery-oriented PFAS surveillance.
References
- Vaitheesvaran P., Warner N., Roberts D., Jeffers T., Zheng X., Cole J., Kutscher D., Driscoll M. Untargeted analysis of volatile PFAS in indoor air by thermal desorption GC high resolution Orbitrap Mass Spectrometer. Thermo Fisher Scientific application/technical report, 2026.
- Thermo Fisher Scientific. Enhance sensitivity using variable electron voltage (VeV) on Orbitrap Exploris GC Mass Spectrometers. Technical Note 000769.
- Thermo Fisher Scientific. Quantitation of volatile PFAS in environmental samples using SPME Arrow and Orbitrap Exploris GC. Application Note 003507.
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