Routine Determination of Trifluoroacetic Acid (TFA) and Difluoroacetic Acid (DFA) in Surface and Drinking Water by Direct Injection Using UPLC-MS/MS

Importance of the Topic

The ubiquitous presence of ultra-short-chain PFAS such as trifluoroacetic acid (TFA) and difluoroacetic acid (DFA) in surface and drinking water poses environmental and health concerns. Regulatory bodies have established guidance values, necessitating sensitive and high-throughput methods for routine monitoring.

Objectives and Study Overview

This study aimed to develop and validate a direct injection UPLC-MS/MS protocol for quantifying TFA and DFA in various water matrices. Performance was assessed by spiking drinking and surface waters at multiple levels and comparing quantitation against standard addition.

Methodology and Instrumentation

Samples were prepared by adding isotopically labelled internal standards (TFA-13C2 and DFA-13C2) directly to water in polypropylene vials. No cleanup or concentration steps were required. Instrumentation

• UPLC: ACQUITY UPLC I-Class PLUS with Flow Through Needle and PFAS-free PEEK lines
• MS: Xevo TQ-XS triple quadrupole in negative ESI mode
• Column: Atlantis Premier BEH C18 AX (1.7 μm, 2.1×100 mm) at 60 °C
• Mobile phase: 2 mM ammonium acetate with 0.001% formic acid, isocratic at 0.5 mL/min
• Injection: 20 μL; run time: 7 min; sample temperature: 15 °C

Calibration standards ranged from 10 to 25 000 ng/L and recovery spikes were performed at 300, 500, and 1000 ng/L with three replicates per matrix.

Results and Discussion

Calibration curves exhibited excellent linearity (R2 > 0.9995, 1/X weighting) with residuals within ±20%. A limit of quantification of 10 ng/L was achieved without SPE. Recoveries ranged from 80% to 110% with RSDs ≤ 9% (except 19% RSD for TFA at low-level hard water). Retention time stability was confirmed with RSDs ≤ 3% across matrices and ≤ 0.9% over 200 consecutive injections. Sample pH variations impacted retention shifts, effectively mitigated by matching standard matrix conditions.

Benefits and Practical Applications

• Minimal sample preparation accelerates throughput and reduces contamination risk
• High sensitivity for low-level detection and quantification
• Rapid analysis (7 min) suitable for routine screening
• Applicable to diverse drinking and environmental water types

Future Trends and Opportunities

Integration of automated sample handling and field-deployable UPLC-MS/MS systems for on-site monitoring. Expansion to a broader PFAS panel including emerging ultra-short analogues. Implementation of nano-LC and advanced ionization techniques to further lower detection limits. Adoption of green analytical chemistry practices to minimize solvent and consumable use.

Conclusion

The direct injection UPLC-MS/MS method using an Atlantis Premier BEH C18 AX column and a Xevo TQ-XS detector provides a robust, sensitive, and efficient solution for routine determination of TFA and DFA in surface and drinking water. Validation results support its use for regulatory compliance and environmental surveillance.

References

1. Scheurer M, Nödler K, Freeling F, et al. Small, mobile, persistent: Trifluoroacetate in the water cycle – Overlooked sources, pathways, and consequences for drinking water supply. Water Research. 2017;126:460–471.
2. Björnsdotter MK, Yeung LWY, Kärrman A, et al. Challenges in the analytical determination of ultra-short-chain perfluoroalkyl acids and implications for environmental and human health. Analytical and Bioanalytical Chemistry. 2020;412:4785–4796.
3. European Fluorocarbons Technical Committee. TFA as an atmospheric breakdown product. EFCTC website. Accessed May 2022.
4. Waters Corporation. Atlantis Premier BEH C18 AX Column Care and Use Manual. 2021.