Comprehensive and Robust Analysis of Ultrashort- to Long-Chain PFAS, PAE, OPE, and PAH

Significance of the topic

Comprehensive, sensitive and selective analysis of ultrashort- to long-chain per- and polyfluoroalkyl substances (PFAS), together with co-occurring classes such as phthalate esters (PAE), organophosphate esters (OPE) and polycyclic aromatic hydrocarbons (PAH), is essential for accurate atmospheric exposure assessment and regulatory monitoring. These compound classes are persistent, bioaccumulative, and toxic; ultrashort-chain PFAS (e.g., trifluoroacetic acid, TFA) are increasingly recognized as widespread and underestimated atmospheric contaminants. A unified analytical workflow that reduces solvent use, minimizes in-source fragmentation and covers wide volatility/polarity ranges streamlines routine environmental monitoring and improves data quality for risk assessment.

Objectives and overview of the study

This application note evaluates a solvent-free, SPME-based sampling and dielectric barrier discharge ionization (DBDI) soft-ionization workflow using Plasmion SICRIT directly coupled to an Agilent Revident LC/Q-TOF. The goals were to:

• Enable simultaneous detection of C2–C8 PFAS alongside PAEs, OPEs and PAHs in PM2.5 samples;
• Reduce in-source fragmentation (ISF) compared with conventional LC‑ESI‑MS;
• Deliver high mass accuracy, low limits of detection (LOD), and robust quantification using PRM on the Revident Q‑TOF;
• Demonstrate the workflow on seasonal real PM2.5 samples from Zhengzhou (Dec 2023–Aug 2024).

Methodology

The analytical workflow combined solvent-free solid-phase microextraction (SPME) sampling with a SICRIT dielectric barrier discharge-based soft ionization source interfaced to an Agilent Revident LC/Q-TOF operating in both positive and negative polarities. Key method features included:

• SPME sampling/desorption: automated desorption from fibers in a GC/SPME module; optimized extraction time 40 min and desorption ~230–240 °C depending on analyte class; different fiber chemistries used for PFAS (85 µm polyacrylate) versus PAEs/OPEs/PAHs (65 µm DVB/PDMS) to maximize uptake across polarity ranges.
• SICRIT DBDI soft ionization: operated at 1.6 kV and 15 kHz under ambient pressure to ionize both highly polar ultrashort PFAS and less polar longer-chain PFAS with reduced ISF.
• High-resolution detection and targeted MS/MS: Agilent Revident LC/Q-TOF with PRM acquisition (narrow isolation width ~1.3 m/z) to isolate precursors and acquire high‑resolution fragments, improving selectivity in complex aerosol matrices.
• Data processing: in-house PRM library using MassHunter Qualitative Analysis and Personal Compound Database; quantitative extraction used a 5 ppm mass window and matrix-matched calibration with isotopically labeled internal standards.

Used instrumentation

• SPME system: custom-built SPME holder integrated with GC/SPME module and glass inlet liner (Plasmion GmbH).
• Ion source: Plasmion SICRIT dielectric barrier discharge ion source (Plasmion GmbH, Augsburg, Germany).
• Mass spectrometer: Agilent Revident LC/Q-TOF with temperature-controlled flight tube and PRM capability.
• Data/software: Agilent MassHunter Qualitative Analysis 12.0, MassHunter Personal Compound Database and Library Manager, MassHunter Molecular Structure Correlator; public databases (MassBank, PubChem) used for confirmation.

Main results and discussion

• Mass accuracy and stability: Interday mass errors for representative targets across PFAS, PAEs, OPEs and PAHs were consistently below 0.2 ppm over three days, demonstrating excellent mass stability of the SICRIT–Revident platform.
• Linearity and reproducibility: Calibration exhibited excellent linearity with R2 values >0.995 for all targets and reproducible responses (n=5).
• Sensitivity: LODs were very low across classes. Representative values include FBSA at 0.06 pg/m3 and several PAEs (e.g., DEP at ~0.03 pg/m3). Many PFAS were detected in the sub-pg/m3 to low-pg/m3 range, though a few analytes (e.g., PFOA) showed higher LODs (~6.97 pg/m3), reflecting differing ionization/response efficiencies by compound.
• In-source fragmentation (ISF): The SICRIT DBDI approach substantially reduced ISF for PFAS relative to reported LC‑ESI results. Most PFAS exhibited ISF ratios below 20% (calculated as area of ISF ions divided by total ion area), whereas literature reports LC‑ESI ISF often >60%. An exception in this dataset was GenX, which showed a higher ISF ratio (~68%), indicating compound-specific fragmentation behavior still needs attention.
• PRM selectivity: Quadrupole isolation prior to fragmentation improved the specificity of fragment assignment in complex PM2.5 matrices and reduced interference from coeluting ions, enhancing unambiguous identification.
• Real sample findings: Application to seasonal PM2.5 from Zhengzhou detected ubiquitous occurrence of the studied classes and revealed distinct phase partitioning and seasonal concentration trends (e.g., variability in TFA, PFCAs, PAHs, PAEs, OPEs and FASA-type compounds across seasons).

Benefits and practical applications of the method

• Unified, solvent-free workflow: SPME combined with SICRIT eliminates solvents and reduces consumable contamination, beneficial for trace-level PFAS work where blanks are a concern.
• Broad compound coverage: Soft DBDI ionization enables sensitive detection from ultrashort volatile PFAS (C2–C4) to less polar long-chain PFAS and multiple co-occurring organic pollutants in a single workflow.
• Improved spectral interpretability: Lower ISF and high-resolution PRM data enhance confidence in molecular ion detection and structural confirmation.
• Suitability for routine monitoring: The platform demonstrated robustness, high throughput potential and quantification performance suitable for environmental surveillance and regulatory laboratories analyzing PM2.5 and related aerosols.

Future trends and potential applications

• Expansion of target lists and non-target screening: The combination of soft ambient ionization and high-resolution PRM/data-dependent acquisition supports both targeted monitoring and exploratory screening for novel PFAS and transformation products.
• Method transfer and standardization: Wider adoption will require inter-laboratory validation, evaluation of matrix effects across environments, and development of standardized SPME and PRM protocols for regulatory comparability.
• Addressing compound-specific limitations: For analytes showing elevated ISF (e.g., GenX) or lower response, optimized ion-source and PRM collision energy tuning or complementary ionization strategies may further improve quantification.
• Integration with atmospheric chemistry studies: High-sensitivity detection of ultrashort PFAS (e.g., TFA) enables improved source apportionment and transformation studies, informing emission control and remediation strategies.

Conclusion

The solvent-free SPME–SICRIT DBDI platform directly coupled to an Agilent Revident LC/Q-TOF provides a practical, high-performance solution for simultaneous analysis of ultrashort- to long-chain PFAS alongside PAEs, OPEs and PAHs in PM2.5. Key strengths include excellent mass accuracy (<0.2 ppm), strong linearity (R2 > 0.995), low LODs in the sub-pg/m3 to low-pg/m3 range for many targets, and substantially reduced in-source fragmentation for most PFAS compared with conventional LC‑ESI approaches. The workflow reduces solvent consumption, simplifies sample preparation and improves spectral clarity, making it suitable for routine environmental monitoring and research into atmospheric PFAS behavior.

References

• Guo W.; Zhang Y.; Wang Y.; Zhu L.; Cai Z. A Comprehensive, Simple, Robust, and Solvent-Free Method Covering Ultrashort- to Long Chain PFAS in Atmospheric Samples. Analytical Chemistry 2025, 97(27), 14838–14846. DOI: 10.1021/acs.analchem.5c03123
• Arp H. P. H.; Gredelj A.; Glüge J.; Scheringer M.; Cousins I. T. The Global Threat from the Irreversible Accumulation of Trifluoroacetic Acid (TFA). Environmental Science & Technology 2024, 58(45), 19925–19935. DOI: 10.1021/acs.est.4c06189
• Wang K.; Wang R.; Shan W.; Yang Z.; Chen Y.; Wang L.; Zhang Y. Unravel the In-Source Fragmentation Patterns of Per- and Polyfluoroalkyl Substances During Analysis by LC-ESI-HRMS. Environmental Science & Technology 2024, 58(51), 22766–22776. DOI: 10.1021/acs.est.4c08442