Determination and Characterization of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS’s) in Environmental Samples Using UPLC Ion Mobility MS

Significance of PFAS Analysis

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are persistent synthetic compounds widely used in industrial and consumer applications. Their stability leads to environmental accumulation and human exposure, raising health concerns such as endocrine disruption and carcinogenic effects. Accurate detection and differentiation of PFAS isomers in complex environmental matrices are critical for risk assessment, regulatory compliance, and remediation strategies.

Objectives and Study Overview

This study evaluates the combination of ultra-high-performance liquid chromatography (UPLC) with ion mobility mass spectrometry (IMS-MS) as a streamlined workflow for unambiguous identification of PFOS isomers in environmental samples. The key aims are to:

• Resolve PFOS isomers from isobaric biological interferences.
• Capture retention time, accurate mass, fragmentation, and drift time in a single analysis.
• Demonstrate enhanced confidence in isomer assignment in mink liver extracts and other environmental matrices.

Methodology and Instrumentation

The analytical approach entailed:

• Sample Preparation: Homogenization of mink liver, acetonitrile extraction, Oasis WAX solid-phase extraction, ENVI-Carb cleanup, and final reconstitution in ammonium acetate.
• Chromatography: Waters ACQUITY UPLC I-Class with BEH C18 column (100 × 2.1 mm, 1.7 µm) at 50 °C; gradient elution using 2 mM ammonium acetate in water and methanol/acetonitrile (80/20).
• Mass Spectrometry: Waters SYNAPT G2-S HDMS operated in electrospray negative mode; ion mobility separation using CO2/N2 drift gas, wave velocity 400–550 m/s, wave height 40 V; acquisition of precursor and fragment ions (50–600 Da, 10 spectra/s).

Main Results and Discussion

Combining UPLC separation with IMS provided a fourth dimension of separation based on collision cross section. Key findings include:

• Distinct drift times for nine PFOS isomers, enabling separation from taurodeoxycholate (TDCA) and taurochenodeoxycholate (TCDCA) interferences that co-elute chromatographically.
• Generation of mobility-resolved accurate mass spectra and fragmentation patterns for each isomer without interference.
• Demonstration that more linear PFOS isomers exhibit longer drift times than branched analogs, offering structural insight.

Benefits and Practical Applications

This UPLC IMS-MS workflow offers several advantages for environmental PFAS analysis:

• Increased selectivity by orthogonal separation, reducing false positives from isobaric matrix components.
• Consolidation of retention time, drift time, accurate mass, and fragmentation data in a single injection.
• Streamlined sample preparation and MS method development compared with highly specific MRM approaches.
• Improved throughput for routine environmental monitoring and QA/QC laboratories.

Future Trends and Possibilities

Advancements likely to expand the utility of ion mobility in PFAS research include:

• Development of comprehensive drift time and collision cross section libraries for a broader range of PFAS.
• Integration of automated CCS calculation within data processing software.
• Exploration of alternative drift gases to enhance isomer resolution.
• Application to other challenging contaminant classes in complex matrices.

Conclusions

The integration of UPLC with ion mobility MS represents a powerful, orthogonal strategy for isomer-specific PFOS analysis. By resolving co-eluting interferences and capturing multiple identification criteria in a single run, this approach enhances confidence in PFAS characterization and supports more efficient environmental monitoring workflows.

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