Extending PFAS Analytical Workflows with APGC-MS/MS Analysis: A Method for 35 GC-Amenable PFAS Compounds

Importance of the topic

Comprehensive measurement of per- and polyfluoroalkyl substances (PFAS) increasingly requires inclusion of volatile and semi-volatile precursors that are poorly retained by liquid chromatography. These GC-amenable PFAS—including fluorotelomer alcohols, acrylates, methacrylates, acetates, sulfonamides and sulfonamidoethanols—contribute to environmental PFAS burden through direct use, emissions and atmospheric transport and can transform to persistent end-products of toxicological concern. A robust, sensitive GC‑MS/MS approach that integrates with existing LC workflows enables laboratories to characterize a broader suite of PFAS without substantially increasing sample-preparation workload.

Objectives and overview of the study

This application note describes development and optimization of an atmospheric pressure gas chromatography tandem mass spectrometry (APGC‑MS/MS) method for 35 GC‑amenable PFAS. Goals were to achieve sensitive, selective quantitation across multiple PFAS classes; to enable direct injection of extracts prepared for LC‑MS/MS (avoiding solvent exchange); and to define practical instrument and consumable choices that ensure robustness in routine analysis.

Used instrumentation

• Gas chromatograph: Agilent 8890 with 7693A autosampler.
• Column: Rtx‑200 GC capillary, 30 m × 0.25 mm ID, 0.50 µm film.
• Inlet liner: Siltek deactivated straight liner with wool (4.0 × 6.5 × 78.5 mm).
• Mass spectrometer: Waters Xevo TQ Absolute (APGC source) operating in positive ionization with proton transfer.
• Data software: waters_connect for Quantitation.

Methodology and analytical conditions

Standards and calibration

• Native standards from commercial suppliers; isotopically labeled internal standards included.
• Calibration ranges: generally 0.01–50 ng/mL; sulfonamides: 0.10–500 ng/mL due to lower sensitivity.

Sample matrix and injection strategy

• Method designed for extracts following EPA 1633 sample preparation: ~94% methanol, 4% water, 1% ammonium hydroxide, 0.6% acetic acid.
• Injection: pulsed split injection (40 psi until 0.6 min), split ratio 10:1, injection volume 1 µL, injection port 240 °C.
• Autosampler wash: isopropyl alcohol (IPA) and methanol used; IPA shown to reduce sulfonamide carryover.

GC parameters

• Carrier gas: nitrogen at 2 mL/min; makeup gas nitrogen at 300 mL/min.
• Transfer line temperature: 310 °C.
• Column selection determined empirically: thicker film (0.50 µm) and longer column improved peak shape for water-containing extracts and avoided overload/peak splitting.

APGC‑MS/MS source and acquisition

• Ionization: atmospheric pressure proton transfer (water) in positive mode; source temperature 150 °C.
• Standard corona current 1.0 µA, cone gas 250 L/hr, auxiliary gas 150 L/hr.
• Alternative source conditions (corona 3.0 µA, cone 650 L/hr, auxiliary 250 L/hr) optimized specifically for x:1 fluorotelomer alcohols (FTOHs), delivering ~10× improved response for those analytes but not recommended for all analytes simultaneously.
• MRM transitions and detailed method parameters provided in the appendix of the original note.

Main results and discussion

APGC advantages and molecular‑ion preservation

• APGC is a soft ionization technique compared with electron ionization (EI). For example, 8:2 FTOH shows a strong [M+H]+ signal using APGC (m/z 365), whereas EI yields extensive fragmentation and poor molecular‑ion signal; this enables more selective and sensitive MRM transitions and more confident identifications in complex matrices.

Inlet liner and stability

• Reactive sulfonamide analytes degraded rapidly with a Restek topaz liner; switching to a Siltek deactivated liner preserved peak shape and signal stability over >150 injections, making it the recommended liner for routine use.

Peak shape and injection of LC extracts

• Direct injection of LC‑type extracts (methanol/water/acid/base) was possible when using a split injection and a thicker‑film 30 m column. Thinner columns or splitless injections gave broad or split peaks, indicating column overload or inefficient transfer.

Sensitivity, linearity and LLOQs

• Calibration linearity across tested ranges was excellent (R2 > 0.993 for all compounds).
• Lower limits of quantification (LLOQ) across the 35 analytes ranged from 0.005 to 5.0 ng/mL; most compounds exhibited LLOQs below 0.10 ng/mL.
• Comparison with LC‑MS/MS for five overlapping compounds showed APGC provided 20–200× better fg‑on‑column sensitivity for N‑MeFOSA, N‑EtFOSA, N‑MeFOSE and N‑EtFOSE; for FOSA APGC was ~5× less sensitive than LC‑MS/MS, indicating selectivity of technique depends on compound class.

Source condition trade‑offs

• One set of source conditions (standard) provided the best compromise for the majority of analytes. The alternative high‑current / high‑gas set increased sensitivity for x:1 FTOHs but reduced performance for others; laboratories should choose based on target analyte priorities.

Benefits and practical applications

• Integrates with existing LC‑MS/MS PFAS workflows: allows injection of EPA 1633‑style extracts without solvent exchange, reducing sample‑prep time and limiting loss of volatile analytes.
• Sensitive and selective detection of volatile/semi‑volatile PFAS classes that are poorly captured by LC alone, improving comprehensiveness of environmental and product surveillance.
• Robust operational recommendations (Siltek liner, thicker film column, split injection, autosampler wash protocol) reduce degradation and carryover in routine analysis.

Future trends and potential applications

• Broader implementation of APGC‑MS/MS as a complementary platform alongside LC‑MS/MS will enable more complete PFAS mass‑balance and precursor profiling in environmental, food packaging and textile matrices.
• Method adaptation and automation could expand throughput for monitoring programs; additional work may focus on standardization and interlaboratory validation for regulatory use.
• Further optimization of ionization conditions or source design may reduce the need for divergent source settings when analyte classes have conflicting optimal conditions.
• Application to real samples (ongoing in companion notes) will inform transformation pathways and human exposure assessments by revealing volatile precursor distributions that are not apparent from LC‑only analyses.

Conclusion

The presented APGC‑MS/MS method provides a practical, sensitive and robust approach to quantify 35 GC‑amenable PFAS classes and complements LC‑MS/MS workflows. Key operational choices—Siltek deactivated inlet liner, Rtx‑200 30 m × 0.25 mm × 0.50 µm column, split injection and carefully selected APGC source conditions—enable direct injection of LC extracts with LLOQs suitable for trace‑level environmental and product testing. APGC‑MS/MS extends analytical coverage to volatile and semi‑volatile PFAS precursors, improving the ability of laboratories to generate comprehensive PFAS exposure and contamination profiles.

References

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