An Alternative Ionization Technique for Perfluorinated Alkyl Substance (PFAS) Analysis: Evaluating UniSpray for Water and Soil Samples

Importance of the Topic

Perfluorinated alkyl substances (PFAS) are persistent organic pollutants widely detected in water and soils. Regulatory requirements demand ultra-trace analysis, often at ng/L levels, necessitating highly sensitive ionization techniques.

Objectives and Study Overview

The aim was to evaluate UniSpray as an alternative ionization source to negative electrospray ionization (ESI) for routine PFAS analysis in water and soil. Comparative studies focused on signal intensity, signal-to-noise, quantitative accuracy, and robustness across a suite of legacy and emerging PFAS compounds.

Methodology and Used Instrumentation

A range of samples including reagent, surface, ground, influent, and effluent water, plus sand, silt, and clay soils were prepared following ASTM 7979 and ASTM 7968. Samples were spiked with isotopically labeled standards, acidified, and filtered prior to direct injection.

Used Instrumentation

• ACQUITY UPLC H-Class PLUS system with PFAS Analysis Kit (Waters)
• ACQUITY UPLC BEH C18 column (2.1×100 mm, 1.7 µm)
• Xevo TQ-S micro triple quadrupole mass spectrometer
• MassLynx software and UniSpray ion source

Main Results and Discussion

UniSpray demonstrated increased peak area and signal-to-noise for the majority of PFAS tested, with up to fourfold lower detection limits (e.g., GenX). Quantitative accuracy in complex matrices remained consistent with ESI (mean deviation ~6%). Both techniques delivered robust repeatability (%RSD < 15%), with UniSpray showing slightly lower variability due to higher signal intensity.

Benefits and Practical Applications

Enhanced sensitivity reduces limits of quantitation, facilitates automated integration at low concentrations, and may simplify sample preparation. UniSpray’s multimode ionization expands applicability to diverse PFAS, supporting routine environmental monitoring and regulatory compliance.

Future Trends and Potential Applications

UniSpray technology could be adapted for emerging PFAS classes and high-throughput screening. Integration with solid-phase extraction workflows and expanding to non-polar contaminant analysis may broaden environmental and biomedical applications.

Conclusion

UniSpray offers a viable, robust alternative to conventional ESI for LC-MS/MS PFAS analysis, delivering enhanced sensitivity and reliable quantitation in water and soil matrices.

References

1. Lubin A, Bajic S, Cabooter D, Augustijns P, Cuyckens F. Atmospheric Pressure Ionization Using a High Voltage Target Compared to Electrospray Ionization. J Am Soc Mass Spectrom. 2016;28.
2. Lubin A, De Vries R, Cabooter D, Augustijns P, Cuyckens F. An Atmospheric Pressure Ionization Source Using a High Voltage Target Compared to Electrospray Ionization for the LC/MS Analysis of Pharmaceutical Compounds. J Pharm Biomed Anal. 2017;142.
3. Galani JHY, Houbraken M, Van Hulle M, Spanoghe P. Comparison of Electrospray and UniSpray for LC-MS/MS Analysis of 81 Pesticide Residues. Anal Bioanal Chem. 2019;411.
4. Oehrle S. Expanding the Horizon! Analysis of Cyanobacterial Toxins by UPLC/MS/MS Using a UniSpray Ion Source. Presented at 10th US HAB Conference; 2019.
5. Riches E, Bajic S, Langley GJ, Herniman JM. Evaluating the Novel UniSpray Ionization Source for the Analysis of Petroleum Samples. Poster; 2017.
6. Mullin L, Burgess J. Ultra Low-Level Detection of Perfluoroalkyl Substances (PFASs) Using the PFC Analysis Kit. Waters Tech Brief 720005701EN; 2016.
7. ASTM D7979-17. Standard Test Method for Determination of PFAS in Water, Sludge, Influent, Effluent and Wastewater by LC/MS/MS. ASTM International; 2017.
8. Organtini K, Cleland G, Rosnack K. Large Volume Direct Injection Method for PFAS in Water per ASTM 7979-17. Waters App Note 720006329EN; 2018.
9. ASTM D7968. Standard Test Method for Determination of PFAS in Soil by LC/MS/MS. ASTM International; 2017.
10. Organtini K, Rosnack K, Stevens D, Ross E. Analysis of Legacy and Emerging PFAS in Water Using SPE and LC-MS/MS. Waters App Note 720006471EN; 2019.
11. Organtini K, Brinster K, Rosnack K. PFAS in Drinking Water: Extraction Using PS2 Cartridge per EPA 537.1. Waters App Note 720006695EN; 2019.