A Rapid Screening Method for PFAS Analysis (EPA 1633a) Using DART-MS

Significance of the topic

The occurrence of per- and polyfluoroalkyl substances (PFAS) at elevated concentrations in environmental and waste matrices poses analytical challenges, notably carryover in LC-MS/MS workflows that can generate false positives and contaminate subsequent low-level samples. Rapid, high-throughput screening methods are therefore valuable as a triage step to identify samples with high PFAS loads prior to full quantitative confirmation, reducing instrument downtime and improving data quality.

Objectives and study overview

This study evaluated Direct Analysis in Real Time mass spectrometry (DART-MS) as a rapid screening tool for detecting high PFAS concentrations that could cause carryover in standard LC-MS/MS analyses (EPA Method 1633A). The goals were to (1) establish a fast screening workflow (~15 seconds per sample), (2) test reproducibility across selected calibration levels, and (3) characterize matrix effects using environmental water extracts.

Methods and methodology

- Standards and calibration: Analytical standard mixtures (Wellington Laboratories) were combined and diluted in basic methanol to generate calibration solutions mapped to a subset of EPA 1633A concentration ranges. New calibration points (L1–L4) were chosen to target the concentration region where LC-MS/MS carryover typically appears; each point was analyzed in quintuplicate to assess reproducibility.
- Sample preparation: Field samples from the Charles River (MA) were processed by solid-phase extraction (SPE) of 25 mL aliquots using a vacuum manifold. Extracts (100 µL) were spiked with analytes and internal standards (EIS), and 5 µL aliquots were applied to a DART mesh for analysis.
- DART-MS operation: Analyses used an EVOQ DART-TQ+ triple quadrupole mass spectrometer (Bruker) in negative ion mode. DART source temperatures evaluated included 450°C (and 250°C), cone gas pressure was 20 psi, cone temperature 300°C, and grid voltage 50 V. Scan/run time per spot was approximately 15 seconds.

Used instrumentation

- EVOQ DART-TQ+ triple quadrupole mass spectrometer with DART ion source (Bruker Scientific LLC, Billerica, MA).
- Solid-phase extraction vacuum manifold for sample cleanup.
- Analytical standards from Wellington Laboratories (ON, Canada).

Main results and discussion

- Throughput and purpose: The DART-MS protocol provided a rapid screen (~15 s/sample) suitable for identifying samples with PFAS concentrations likely to induce LC-MS/MS carryover, serving as a triage step rather than a full quantitative replacement.
- Reproducibility and linearity: For the 31 PFAS covered by EPA 1633a, quality control metrics and relative standard deviations (RSDs) at the tested calibration points were within the predefined acceptance threshold (<30%) for the majority of analytes, indicating acceptable short-term reproducibility in the targeted concentration window. Some calibration points fell outside acceptable ranges and were highlighted in the study.
- Matrix effects: Measured matrix effects (n=3) for selected PFAS spiked into Charles River extracts showed variable suppression/enhancement: 11Cl-PF3OUdS ~99%, HFPO-DA ~70%, PFBS ~77%, PFDS ~105%, PFNS ~70%, PFHxS ~80%, PFOSA ~88%. These values indicate generally moderate matrix-related signal changes, with PFDS showing slight enhancement and others showing varying degrees of suppression.
- Practical implications: The DART-MS screen detects high-level PFAS that could compromise LC-MS/MS sequences, enabling labs to remove or rerun problematic samples and thereby reduce carryover risk. The method’s speed and minimal sample preparation are major operational advantages.

Benefits and practical applications of the method

- Rapid triage: Short analysis time allows screening of many extracts prior to LC-MS/MS, prioritizing samples for full confirmatory analysis.
- Reduced instrument contamination: Early detection of high PFAS concentrations minimizes carryover into subsequent runs, protecting sensitive analyses at low ng/mL levels.
- Simplified workflow: Minimal aliquot volumes (5 µL) applied to DART mesh reduce sample handling and consumable use compared with longer LC-MS/MS sequences.

Limitations and considerations

• Semi-quantitative nature: DART-MS provides rapid screening but lacks the robustness and sensitivity of full LC-MS/MS quantitation for trace-level PFAS.
• Matrix dependence: Observed matrix effects vary by compound and matrix, requiring case-by-case evaluation and potential matrix-matched controls or correction strategies.
• Calibration scope: The approach focused on a limited calibration window (L1–L4) relevant to carryover detection; samples below that range still require confirmatory LC-MS/MS analysis.
• Method optimization pending: The study notes further optimization (expanded sample types, temperature and ionization parameters) is ongoing to improve performance and applicability.

Future trends and applications

- Method optimization: Systematic evaluation of DART temperatures, mesh substrates, solvent composition, and ion-source conditions to improve sensitivity and reduce matrix effects.
- Automation and integration: Development of automated spotting and plate-handling to increase throughput and reproducibility for routine screening labs.
- Hybrid workflows: Combining DART screening with targeted LC-MS/MS confirmation and selective SPE cleanup strategies to balance speed and quantitative accuracy.
- Broader matrix validation: Extending validation to other environmental and industrial matrices (wastewater, soils, biosolids, food matrices) to define limitations and required adjustments.
- Expanded compound panels: Inclusion of emerging PFAS chemistries and chlorinated or oligomeric PFAS variants to broaden screening coverage.

Conclusion

DART-MS on an EVOQ DART-TQ+ instrument offers a rapid, practical screening tool to identify extracts with elevated PFAS concentrations that pose a risk for LC-MS/MS carryover. The approach demonstrated acceptable reproducibility for many EPA 1633a analytes within the targeted concentration window and moderate, compound-dependent matrix effects in river water extracts. While not a replacement for quantitative LC-MS/MS confirmation, DART screening can improve laboratory throughput, reduce false positives from carryover, and focus confirmatory resources on relevant samples. Continued optimization and broader validation will strengthen its utility in routine PFAS monitoring workflows.

References

1. US EPA Method 1633A for the analysis of PFAS (method framework referenced in the study).
2. Wellington Laboratories, analytical standard mixtures for PFAS (supplier information as cited).
3. Bruker Scientific LLC, EVOQ DART-TQ+ instrument and DART ion source (instrumentation cited in study).
4. Khatami S., Waller S., Covey J., Anthony T., Moskowitz M., Putnam S., Chalom M., Zonderman J., Espourteille F.A., Filipenko A., A Rapid Screening Method for PFAS Analysis (EPA 1633a) Using DART-MS (Bruker application note/technical summary).