Per- and Polyfluoroalkyl Substances in Aqueous Samples: Performance Demonstration of EPA Method 1633 Using High Sensitivity Mass Spectrometry

Significance of the Topic

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that pose analytical challenges due to their low concentrations and diverse chemistries. Recent U.S. EPA regulation (April 2024) of PFAS in drinking water calls for reliable methods to quantify trace levels in various matrices. Implementing EPA Method 1633 in aqueous samples ensures compliance and protects public health.

Objectives and Study Overview

This study evaluates the performance of EPA Method 1633 for PFAS analysis in water, using high-sensitivity LC-MS/MS. Key aims include demonstrating method linearity, determining method detection limits (MDLs), and comparing results to EPA-reported values.

Methodology and Workflow

Sample Preparation and Cleanup:

• Reagent water (500 mL) spiked with isotope-labeled internal standards (EIS) and native PFAS.
• SPE using Biotage EVOLUTE® EXPRESS WAX cartridges (150 mg/6 mL) following a wash, elution, and concentration protocol.
• Filtration through 0.2 µm nylon and transfer to silanized amber vials.

Calibration and QC:

• Calibration curves prepared by serial dilution of PFAS standards in methanol/water mixtures.
• Quality control steps include instrument blanks, method blanks, calibration verifications, and spiked samples over three days.

Instrumentation

LC-MS/MS Analysis:

• Shimadzu LCMS-8060NX triple quadrupole mass spectrometer coupled to Nexera HPLC.
• Analytical column: Shim-pack Scepter C18-120 (3 µm, 2.1 × 50 mm); delay column: Shim-pack Scepter C18-120 (3 µm, 2.1 × 100 mm).
• Mobile phase A: 2 mM ammonium acetate in water; B: LC-MS grade acetonitrile; flow rate 0.4 mL/min; run time 14 min; injection 10 µL; column oven 40 °C.

Main Results and Discussion

Instrument Linearity and Precision:

• Relative standard error (RSE) for target PFAS ranged from 9.8 % to 18.3 %, meeting EPA 1633 criteria (≤ 20 %).

Method Detection Limits:

• Calculated MDLs ranged from 0.10 ng/L (PFEESA) to 1.48 ng/L (5:3 FTCA).
• MDLs achieved with Shimadzu LCMS-8060NX were up to 13.4× lower than EPA-reported values for some compounds.

Matrix and Blank Considerations:

• Method blanks (MDLb) were evaluated; for 21 compounds MDLb values influenced final MDL selection.

Benefits and Practical Applications

The optimized workflow delivers high sensitivity and robust quantification of a broad range of PFAS in water. Laboratories can achieve regulatory compliance and implement routine monitoring for environmental and drinking water safety.

Future Trends and Opportunities

Advancements may include integration of high-resolution MS for non-target PFAS screening, automated sample preparation, miniaturized field-deployable systems, and data analytics driven by AI for faster risk assessment and decision making.

Conclusion

The demonstrated method fulfills EPA 1633 QC requirements, offering superior detection limits and reproducible performance. Its adoption supports accurate PFAS monitoring in environmental and compliance laboratories.

Reference

1. U.S. Environmental Protection Agency. Method 1633: Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS; EPA 1633; January 2024.
2. U.S. Environmental Protection Agency. Appendix B to Part 136: Definition and Procedure for the Determination of the Method Detection Limit—Revision 2; Title 40 CFR; 2024.