ULTIMATE SENSITIVITY FOR THE DETECTION OF PER- AND POLYFLUORINATED ALKYL SUBSTANCES IN ENVIRONMENTAL WATER SAMPLES

Importance of the Topic

Per- and polyfluorinated alkyl substances (PFAS) are persistent environmental contaminants found in water sources worldwide. Regulatory agencies are tightening limits for PFAS in drinking and surface waters, driving the need for highly sensitive analytical methods. Direct injection techniques, combined with advanced mass spectrometry, offer rapid, low-contamination testing and higher throughput compared to traditional solid phase extraction approaches.

Study Objectives and Overview

This study evaluated the capability of the Xevo TQ Absolute Tandem Quadrupole Mass Spectrometer to detect 33 targeted PFAS in various water matrices using a 10 µL direct injection. Objectives included determining method detection limits (MDLs), demonstrating calibration linearity, assessing method precision, and measuring PFAS concentrations in real samples (drinking water, groundwater, surface water, and wastewater influent).

Applied Methodology and Instrumentation

Sample Preparation:

• Water samples (5 mL) spiked with isotopically labeled standards.
• Dilution with 5 mL methanol and addition of 10 µL acetic acid.
• Syringe filtration through a 1.0 µm glass fiber filter.

Chromatography and Detection Conditions:

• LC System: ACQUITY UPLC I-Class Plus with PFAS kit.
• Column: ACQUITY BEH C18, 2.1×100 mm, 1.7 µm, maintained at 45 °C; sample tray at 10 °C.
• Mobile phases: water + 2 mM ammonium acetate (A), methanol + 2 mM ammonium acetate (B); 10 µL injection.
• MS System: Xevo TQ Absolute MS; ESI− mode, capillary 0.5 kV, desolvation 350 °C (900 L/h), source 100 °C, cone gas 150 L/h.

Main Results and Discussion

MDLs for 33 PFAS ranged from 0.8 to 2.0 ng/L, with some compounds elevated due to background contamination. Calibration curves (0.5–250 ng/L) showed excellent linearity and deviation within acceptable limits. In wastewater spiking experiments, PFOS isomers were resolved and quantified at sub-ng/L levels. Precision across seven continuing calibration verifications (10 ng/L) yielded ≤10% RSD for all analytes. Real sample analysis detected multiple PFAS below 5 ng/L, demonstrating method robustness across matrices.

Benefits and Practical Applications

The combination of enhanced negative ion sensitivity and direct injection:

• Eliminates large-volume SPE steps, reducing solvent use and contamination risk.
• Requires only 10 µL injection, preserving chromatographic performance and column life.
• Enables high throughput analysis of environmental and drinking water samples.

Future Trends and Potential Uses

Advancements in sensitivity and source design will further lower detection limits for emerging PFAS. Integration with automated sampling and data processing platforms can streamline monitoring programs. Expanded compound coverage, including novel PFAS precursors and degradation products, will enhance environmental risk assessments and compliance efforts.

Conclusion

Direct injection on the Xevo TQ Absolute MS provides a fast, accurate, and sensitive approach for multi-PFAS analysis in varied water matrices. Achieving MDLs below 2 ng/L with minimal sample preparation, this method supports regulatory monitoring and research applications with improved throughput and reduced maintenance demands.

Reference

1. Organtini K et al. Waters Application Note 720006329, 2018.
2. Willmer H et al. Waters Application Note 720007413, 2021.
3. ASTM D7979-17, Standard Test Method, ASTM International, 2017.