Reliable Ultra Short Chain PFAS Analysis in Water and Landfill Groundwater

Significance of the topic

The increasing occurrence of ultrashort‑chain per‑ and polyfluoroalkyl substances (PFAS) such as trifluoroacetic acid (TFA) and difluoroacetic acid (DFA) in environmental waters creates an analytical challenge because these analytes have minimal retention on conventional reversed‑phase columns and are prone to background contamination. Reliable, high‑throughput methods capable of separating, detecting, and quantifying ultrashort PFAS in high‑ionic‑strength and complex groundwater matrices are therefore essential for monitoring, regulatory compliance, and risk assessment.

Objectives and study overview

This application study evaluated the analytical performance of the Agilent Altura Poroshell PFAS column in combination with an Agilent InfinityLab Poroshell 120 PFAS delay column and a 6495D triple‑quadrupole LC/MS (LC/TQ) platform. Goals were to: quantify method detection limits (MDLs) for multiple ultrashort PFAS; assess retention‑time stability in high‑salt synthetic water; measure spike recoveries and precision; and test the workflow on real landfill groundwater samples. Results were also compared for PFBA against an external laboratory using EPA Method 1633A (SPE + LC/MS/MS) to evaluate comparability.

Methodology and experimental design

Key experimental features:

• Analytes: a suite of ultrashort PFAS (including TFA, DFA, PFPrA, PFMeS, PFBA, PFPrS, PFOMAA, PFEtS and a bis(trifluoromethane)sulfonimide salt standard) with isotopically labeled analogs where available.
• Sample matrices: RO water calibration standards, a laboratory synthetic (LS) high‑ionic‑strength water formulated per EPA 557 (nitrate 20 mg/L, bicarbonate 150 mg/L, chloride 250 mg/L, sulfate 250 mg/L) to challenge ionic effects, and real groundwater samples from seven landfill monitoring wells.
• Sample prep: simple direct injection workflow — samples vortexed, centrifuged, supernatant transferred to vials and fortified with labeled internal standards (0.1 ng/mL).

Chromatographic and MS conditions (select highlights):

• Column: Agilent Altura Poroshell PFAS, 2.1 × 100 mm, 2.7 µm.
• Delay column: Agilent InfinityLab Poroshell 120 PFAS delay column, 4.6 × 30 mm.
• LC: Agilent 1290 Infinity III system (modified with PFC‑free conversion kit).
• Mobile phases: A = 0.1% acetic acid in water; B = 90:10 acetonitrile:water with 10 mM ammonium acetate. Flow 0.5 mL/min, 40 °C, 25 µL injection, run time ~12.5 min.
• MS: Agilent 6495D triple quadrupole with JetStream source; optimized source and MRM transitions to reduce TFA baseline interference.

Instrumentation used

Instrument list and key consumables used in the study:

• Agilent 1290 Infinity III LC system (high‑speed pump, multisampler, multicolumn thermostat) with PFC‑free HPLC conversion kit.
• Agilent Altura Poroshell PFAS column, 2.1 × 100 mm, 2.7 µm (p/n 227210‑007).
• Agilent InfinityLab Poroshell 120 PFAS delay column, 4.6 × 30 mm (p/n 027403‑007).
• Agilent 6495D triple‑quadrupole LC/MS with Agilent JetStream source.
• Chemicals: LC/MS‑grade acetonitrile and methanol, acetic acid, ammonium acetate, Milli‑Q and RO water; standards from Cambridge Isotopes, Wellington Labs, Sigma‑Aldrich, Accustandard.

Results and discussion

Detection limits and contamination control:

• Calculated method detection limits (MDLs) across the analyte list translated to the low‑ng/L range (approximately 4–54 ng/L). TFA and PFMeS were limited by background in method blanks rather than spike‑based estimates; environmental lab ambient TFA was persistent even when instrument blanks were clean.
• Because background TFA was ubiquitous in the mixed‑use laboratory, the authors used elevated TFA spike levels for MDL calculations and recommend preparing samples in TFA‑free spaces when possible.

Retention time stability under ionic strength:

• Comparison between RO water standards and high‑ionic synthetic water showed preserved peak shapes (Gaussian) and robust RT stability; the largest observed retention time shift was ~0.1 minute (PFPrA), demonstrating reliable chromatographic behavior in salt‑rich matrices.

Spike recovery and precision in synthetic water:

• Synthetic water was spiked at three levels (lowest: 0.01 ng/mL for most analytes; 0.1 ng/mL for TFA). Most analytes achieved recoveries within 70–130% and relative standard deviations (RSDs) <15% across replicates (n = 4).
• DFA showed poor recovery and poorer precision, attributed to matrix suppression from the high salt load and the absence of an isotopically labeled DFA standard. DFA quantitation was surrogate‑corrected using 13C2‑TFA, which degraded accuracy and reproducibility.
• Isotopically labeled internal standards improved quantitation for several analytes, emphasizing their importance for ultrashort PFAS analysis.

Field sample results and comparison to EPA 1633A:

• Groundwater from seven landfill sites consistently contained TFA in all samples; other frequently detected analytes included PFPrA, PFMeS, DFA and PFBA.
• Retention times in field samples matched calibration standards closely, and internal standard behavior (recoveries 66–99%) was consistent.
• PFBA results from the direct‑injection Altura/Poroshell workflow correlated well with results from an external laboratory using EPA Method 1633A (SPE + LC/MS/MS) — correlation coefficient r ≈ 0.84 (p < 0.001). The SPE‑based 1633A method achieved lower LODs due to concentration by extraction, while the direct‑injection approach provided a faster, simpler workflow with good comparability across the concentration range tested.

Benefits and practical applications of the method

Practical advantages observed and inferred:

• Robust retention and separation of ultrashort PFAS: Altura Poroshell PFAS plus Poroshell PFAS delay column provide stable, reproducible chromatographic performance even in high‑salt matrices.
• Streamlined sample preparation: direct injection minimizes preparation time, reduces extraction bias and lowers consumable use compared with SPE workflows.
• Fit for monitoring: MDLs in the low‑ng/L range and consistent field performance make this workflow suitable for routine landfill groundwater monitoring and screening for ultrashort PFAS presence and trends.
• Compatibility with regulatory methods: good agreement with EPA 1633A PFBA results supports use as a complementary or screening approach where SPE is not feasible or where throughput is prioritized.

Future trends and potential uses

Key developments and recommended directions:

• Broader availability of isotopically labeled standards for ultrashort PFAS (e.g., DFA) will be critical to improve quantitation accuracy and precision in complex matrices.
• Continued refinement of contamination control (laboratory design, PFC‑free consumables, dedicated TFA‑free spaces) will reduce blank limitations for TFA and similar compounds.
• Advances in instrument sensitivity and source design will lower detection limits for direct‑injection workflows, narrowing the gap with SPE‑based methods.
• Method harmonization and interlaboratory comparisons (including wider adoption and adaptation of EPA 1633A) will support regulatory monitoring programs for ultrashort PFAS and improve data comparability.
• Application expansion: the described workflow is suitable for rapid screening in environmental monitoring, preliminary site assessments, and as a companion method to SPE‑concentrated analyses for confirmation and lower‑level quantitation.

Conclusion

The combination of the Agilent Altura Poroshell PFAS analytical column, a Poroshell PFAS delay column, and a 6495D triple‑quadrupole LC/MS provides a reliable, reproducible workflow for analysis of ultrashort‑chain PFAS in both low‑salt and high‑ionic‑strength matrices. The method delivers low‑ng/L MDLs for most targets, robust retention‑time stability (≤0.1 min shift in ionic matrices), and acceptable recoveries and precision for the majority of analytes tested. Limitations include blank‑limited TFA and PFMeS, and analytes lacking isotopically labeled surrogates (notably DFA) that suffer matrix suppression and reduced quantitative performance. Overall, this direct‑injection approach offers environmental laboratories a fast, fit‑for‑purpose option for routine ultrashort PFAS screening and monitoring, complementary to SPE‑based regulatory methods for lower detection limits.

References

1. Arp, H. P. H.; Gredelj, A.; Glüge, J.; Scheringer, M.; Cousins, I. T. The Global Threat from the Irreversible Accumulation of Trifluoroacetic Acid (TFA). Environmental Science & Technology 2024, 58(45), 19925–19935.
2. U.S. Environmental Protection Agency. Method 1633A: Analysis of Per‑ and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC‑MS/MS (EPA 820‑R‑24‑007), 2024.
3. U.S. Environmental Protection Agency. Method 557: Determination of Haloacetic Acids, Bromate, and Dalapon in Drinking Water by IC‑ESI‑MS/MS (EPA Document No. 815B09012), 2009.
4. U.S. Environmental Protection Agency. Definition and Procedure for the Determination of the Method Detection Limit (MDL), Revision 2 (EPA 821‑R‑16‑006), 2016.