Direct Injection Analysis of PFAS in Seawater UsingtheShimadzuLCMS-8060RX

Significance of the topic

Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative contaminants of high regulatory and public-health concern. Monitoring PFAS in seawater is critical because coastal seawater is often used as feed for desalination plants and because marine ecosystems can act as sinks and vectors for PFAS. Traditional workflows rely on solid-phase extraction (SPE) to remove salts and concentrate analytes, but SPE is labor intensive and increases the risk of background contamination. A validated direct injection LC-MS/MS approach can significantly increase laboratory throughput, lower contamination risk, and provide sensitive trace-level PFAS data for environmental surveillance and regulatory compliance.

Study objectives and overview

This application note describes the development and validation of a direct-injection LC-MS/MS method for determination of 25 PFAS in seawater using the Shimadzu Nexera LC-40 UHPLC coupled to the LCMS-8060RX triple quadrupole mass spectrometer. Key aims were to: (1) manage the high salt load inherent to seawater to protect ion-source robustness, (2) maintain analytical sensitivity and chromatographic fidelity for a broad PFAS suite, and (3) avoid extensive sample preparation while achieving regulatory-grade performance (linearity, recovery, precision) over 0.5–50 ng/L.

Methodology

Sample preparation and injection:

• 600 µL seawater mixed with 400 µL acidified organic reagent containing isotopically labeled internal standards (25 ng/L) and vortexed for 5 minutes.
• Direct injection volume: 50 µL; co-injection with water from the SIL-40 autosampler to reduce effective organic strength at the column inlet without diluting analytes.

Chromatographic and MS conditions (summary):

• Column: Shim-pack GIST-HP C18, 75 mm × 3 mm, 2 µm.
• Flow rate: 0.4 mL/min; column oven: 45 °C; run time: 16 min.
• Mobile phase A: 10 mM ammonium acetate in water + 0.1% formic acid; B: methanol. Gradient modified to push salts out early and retain PFAS on the reversed-phase column.
• Ionization: Heated-ESI; interface temp ~100 °C; DL 150 °C; heating block 250 °C; nebulizing/heating/drying gas flows as reported.
• Calibration: internal standard calibration, 1/x weighted linear regression, range 0.5–50 ng/L, intercept forced through zero.

Salt-management strategy:

• PFAS-Free Kit on the Nexera system to minimize background PFAS from tubing, filters and consumables, plus a delay column to shift background PFAS retention.
• Automated FCV-20AH2 flow-control valve programmed to divert the early eluting column effluent (salt fraction) to waste; valve switched to MS only after salts eluted.
• Time-resolved verification of salt elution using an ion chromatography (IC) system to confirm conductivity profile and proper waste diversion window.
• Co-injection of water (autosampler feature) to improve retention and peak shape of early-eluting PFAS when samples are diluted with organic solvent.

Used instrumentation

• Shimadzu LCMS-8060RX triple quadrupole mass spectrometer.
• Nexera LC-40 Series UHPLC (including SIL-40 autosampler and PFAS-Free Kit).
• FCV-20AH2 flow-control valve for automated effluent diversion.
• Shim-pack GIST-HP C18 column (75 × 3 mm, 2 µm).
• Nexera IC system for time-resolved conductivity checks of waste fractions.
• Software: LabSolutions Insight for data acquisition and processing.

Main results and discussion

Linearity and calibration:

• Excellent linearity across 0.5–50 ng/L for all target PFAS (R² > 0.99), using isotopically labeled internal standards and 1/x weighting.

Recovery and precision:

• Recoveries for 25 PFAS at spike levels 2, 5, and 10 ng/L generally ranged from 70–120% (exceptions: PFOS >120% at 2 ng/L; 11Cl-PF3OUdS <70% at 10 ng/L).
• Precision: RSDs <10% for 20/25 compounds at 2 ng/L and <15% for the remaining five; at 5 and 10 ng/L all compounds showed RSD <10%.

Salt control and robustness:

• Direct injection of seawater without mitigation rapidly deposits salts on ESI components (visible after two 50 µL injections). The combined strategy (optimized gradient, FCV diversion, PFAS-free consumables, and water co-injection) prevented visible salt buildup after seven consecutive high-salinity injections and a QC standard.
• Time-resolved IC analysis of waste fractions confirmed that inorganic salts eluted within the planned diversion window, ensuring salts were directed to waste before PFAS fraction reached the MS.

Chromatographic performance:

• Co-injection of water improved retention and peak shape for early-eluting, polar PFAS that were otherwise compromised by the organic diluent used to solubilize analytes.

Practical benefits and applications

• Eliminates labor-intensive SPE steps, reducing analysis time, consumables use, and cross-contamination risk.
• Maintains trace-level sensitivity suitable for environmental monitoring and supports compliance with regulatory drivers such as EU Directive 2020/2184 and US EPA Method 1633A.
• High-throughput capability suited for routine surveillance of seawater, desalination feed-water monitoring, and marine pollution studies.

Limitations and considerations

• Some analytes showed recovery deviations and may require compound-specific attention (e.g., PFOS and 11Cl-PF3OUdS in this dataset).
• Method robustness depends on correct timing of valve switching and stability of the co-injection procedure; laboratories must validate timing for different seawater matrices and salinities.
• While visible salt deposits were avoided in the tested sequence, periodic maintenance and source inspection remain recommended for long-term operation and varying sample loads.

Future trends and potential uses

• Broader PFAS panels: expanding analyte lists to include new PFAS and transformation products as standards become available.
• Lowering detection limits through improved ionization strategies, optimized MS acquisition, and automated sample-introduction workflows.
• Integration with orthogonal techniques (e.g., IC or high-resolution MS) for improved speciation of brominated/chlorinated PFAS and distinguishing background contaminants.
• Automation and remote monitoring: coupling this direct-injection approach with automated sampling and laboratory information management systems (LIMS) for continuous coastal surveillance.
• Method adaptation to diverse seawater matrices: validating across different salinities, temperatures and organic loads encountered in global coastal environments.

Conclusion

The described direct-injection LC-MS/MS workflow using the Shimadzu Nexera LC-40 with PFAS-Free kit and LCMS-8060RX provides a practical, high-throughput solution for quantifying 25 PFAS in seawater at sub-ng/L to tens of ng/L levels. Key enablers are an optimized chromatographic gradient, automated FCV-based effluent diversion to remove salt fractions, water co-injection to stabilize chromatographic behavior of polar PFAS, and PFAS-free consumables/delay column to reduce system background. The approach substantially reduces sample preparation, achieves regulatory-grade linearity, acceptable recoveries and precision, and demonstrates instrument robustness for repeated direct injections of high-salinity samples.

References

1. Directive (EU) 2020/2184 of the European Parliament and of the Council of 16 December 2020 on the quality of water intended for human consumption.
2. U.S. EPA. Method 1633A: Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS. Revision A, December 2024.