Direct Analysis of PFOS and PFOA in Tap Water Using Triple Quadrupole LC/MS/MS

Importance of the Topic

Perfluorooctane sulfonic acid PFOS and perfluorooctanoic acid PFOA are persistent organofluorine compounds with potential health hazards due to their stability and bioaccumulation

Regulatory bodies have set stringent limits for their concentration in drinking water making reliable analytical methods critical for water quality management

Objectives and Overview of the Study

The study aimed to evaluate a direct injection method using the LCMS 8060NX for quantifying PFOS and PFOA in tap water without a preconcentration step

Key goals included demonstrating sensitivity below one tenth of the provisional target value of 50 ng per liter and verifying method accuracy and reproducibility in real samples

Methodology

Mixed standard solutions ranging from 1 to 50 ng per liter were prepared in a water methanol 90 10 matrix with 10 ng per liter of 13C8 labeled internal standards

Calibration curves were constructed using the internal standard method and showed linearity across the tested range with correlation coefficients exceeding 0.999

Repeatability tests were performed by five replicate injections at low concentration levels to assess precision

Used Instrumentation

HPLC system Nexera X3 equipped with a Shim pack Velox SP C18 analytical column and a Shim pack XR ODS II delay column

Triple quadrupole mass spectrometer LCMS 8060NX operating in negative electrospray ionization mode

MRM transitions were monitored for PFOS m/z 498.90>79.95 and PFOA m/z 412.90>169.10 with internal standards 13C8 PFOS and 13C8 PFOA

Key Results and Discussion

Calibration curves for both PFOS and PFOA were highly linear in the 1 to 50 ng per liter range with r2 values above 0.999

Accuracy at 1 ng per liter and 5 ng per liter levels ranged from 100 to 107 with repeatability below 3.3 percent RSD

In tap water spike tests at 5 ng per liter mean recovery rates were approximately 110 percent with RSD below 4 percent demonstrating excellent method performance

The use of a delay column effectively separated background system contamination from sample peaks

Benefits and Practical Applications

This direct injection approach eliminates the need for time consuming concentration steps such as solid phase extraction

It delivers high sensitivity and robustness for monitoring PFOS and PFOA in drinking water at low nanogram per liter levels

Suitable for routine environmental analysis and compliance testing in water quality laboratories

Future Trends and Potential Applications

• Extension of the method to other per and polyfluoroalkyl substances PFAS
• Development of higher throughput workflows and automation for large sample sets
• Miniaturized or field deployable mass spectrometry for on site water testing
• Non targeted screening and suspect screening enabled by advanced data acquisition strategies
• Integration with chemometric and machine learning tools for improved data interpretation

Conclusion

The LCMS 8060NX coupled with direct injection provides a sensitive accurate and reproducible method for PFOS and PFOA analysis in tap water

It meets regulatory requirements for low level quantitation and streamlines workflow by removing concentration steps

Reference

1. The Stockholm Convention on Persistent Organic Pollutants POPs Annex A Elimination as of May 2019
2. The Stockholm Convention on Persistent Organic Pollutants POPs Annex B Restriction as of May 2019
3. Ministry of Health Labour and Welfare Notice on Water Quality Standards Enforcement Regulations October 10 2003 revision March 30 2020