Reducing PFAS interferences during human plasma and serum analysis with accurate mass spectrometry

Resolve and identify endogenous compounds using the X500R QTOF system

Craig M. Butt,1 Robert A. Di Lorenzo,2 Casey Burrows,1 Frederick G. Strathmann,3 Joseph W. Homan3
SCIEX, USA, 2SCIEX, Canada, 3NMS Labs, PA, USA


Co-eluting interferences in biological matrices have been shown for PFOS and PFHxS when monitoring the [SO3]- fragment ion. Here, accurate mass spectrometry was used to mass resolve PFOS & PFHxS from these interferences. The separation used was able to chromatographically resolve the interferences using a 6.5 minute gradient. The interferences were then characterized using their MS/MS fragmentation spectra and library searching.

10464 x500


Poly- and perfluorinated alkyl substances (PFAS) are well-known anthropogenic contaminants and are detected worldwide in most environmental media, including air, water and soil. Widespread human exposure has resulted in the nearly ubiquitous detection of PFAS in human serum.1,2 Accurate and robust analytical methods are needed to quantify the total PFAS burden in humans and to understand potential health risks.

PFAS serum analysis is challenging due to matrix complexity and potential endogenous interferences. Specifically, co-eluting interferences have been shown for perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonate (PFHxS) when monitoring the [SO3]- fragment ion (m/z 80) during traditional MRM analysis.3 In this application note, a high resolution, high mass accuracy mass spectrometer was used to mass resolve PFOS and PFHxS from serum interferences. The interferences were characterized using their fragmentation patterns and through comparison with MS/MS libraries. Finally, the serum interferences were chromatographically resolved using a 6.5 min gradient (Figure 1).  

Figure 1. Confirming chromatographic separation of PFOS interference. A wide XIC chromatogram (498.53–499.33 Da) for a pooled plasma/serum sample was generated from the TOF MS data (top panel) and multiple chromatographic peaks were observed. This wide extraction width simulates what would be isolated by Q1 in a typical MRM experiment. The precursors present in the TOF MS within the peaks at RT 3.299 and 3.394 (bottom left) and at RT 3.556 (bottom right) show the exact masses for 1) PFOS at m/z 498.9302, and to show that the major interference at m/z 498.2886 for 2) the plasma/serum matrix peak has been chromatographically resolved, and that they can easily be mass resolved by narrowing the XIC extraction width to a standard 20 mDa.

Benefits of HRMS for PFAS serum and plasma analysis

  • Serum interferences can be mass resolved using precursor ion accurate mass to improve data quality.
  • Time-of-flight (TOF) MS spectrum can be used to confirm and identify interferences that are chromatographically separated