Application of Quadrupole-Orbitrap MS for Enhanced-Sensitivity in Targeted and Non-Targeted Analysis of PFAS in Environmental Waters

Polyfluoroalkyl Substances (PFAS) in the Environment
Oral Presentation

Presented by E. George
Prepared by L. Ferguson, A. Joyce
Duke University, Gross Hall, Room 379 ,, Dept. of Civil & Environ. Engineering, Durham, North Carolina, 27708, United States


Contact Information: lee.ferguson@duke.edu; (919) 660-5460


ABSTRACT

Introduction
Polyfluorinated alkyl substances (PFAS) are ubiquitous and persistent pollutants, which are introduced to natural and engineered environments through use and disposal of consumer products, industrial coatings, firefighting foams, and other sources. There are over 5,000 known and suspected PFAS compounds, many of which are of concern for contamination of drinking water sources due to their high mobility and low degradability. Low (part-per-trillion) health advisory thresholds for many PFAS have been proposed by local and national governments, and this has led to a critical need for analytical methods that are capable of detecting and characterizing a broad range of PFAS compounds, while allowing quantitation at extremely high senstitivity.

Methods
We have utilized a modified Thermo Scientific Orbitrap Exploris mass spectrometer with S-lens interface to explore the potential for low parts-per-trillion direct detection and quantitation of > 48 priority PFAS compounds in water, while also allowing screening of suspected PFAS through high-resolution/accurate mass (HR/AM) spectrometry. Specifically, we have used both direct-injection and solid-phase extraction to analyze drinking water sources from North Carolina impacted by known PFAS sources. Quantitation by HR/AM mass spectrometry was compared to LC-MS/MS results obtained using a Thermo Scientific TSQ Altis triple quadrupole MS. Suspect and non-targeted analysis of PFAS in drinking water sources and in aqueous film-forming-foam (AFFF) concentrates was performed using the modified Exploris system in data-dependent MS/MS mode with the AcquireX sequential inclusion/exclusion approach.

Preliminary Data
Comparison of direct-injection LC-MS(/MS) analysis of PFAS-contaminated water using HR/AM mass spectrometry vs. triple-quadrupole MS/MS revealed that the modified Thermo Scientific Orbitrap Exploris mass spectrometer with S-lens interface gave sensitivities within a factor of 2 – 5 fold-lower vs. the TSQ Altis, resulting in detection limits for most of the 48 PFAS quantified between 2 and 15 ng/L (parts-per-trillion) without need for solid-phase extraction. In cases of perfluorinated alkyl acids (PFCAs) and next-generation ether-acid PFAS compounds, facile fragmentation in the ion source led to decarboxylation and reduction in the signal for [M-H]- ions in negative ion electrospray analysis. The application of internal mass calibration resulted in mass accuracies < 1 ppm in all measurements. This enabled very narrow extracted ion chromatogram windows, leading to reduced background and enhanced sensitivity in complex water samples, relative to triple-quadrupole MS/MS approaches. Data-dependent MS/MS using the AcquireX sequential injection method on the modified Exploris system allowed comprehensive characterization of PFAS in both water extracts and AFFF concentrates. Specifically, the combination of rich HR/AM MS/MS spectra with both spectral library matching and compound database searching led to increased annotation of novel and poorly studied PFAS in these samples. Finally, the implementation of a combined mass defect and reverse isotope ratio filtering approach allowed for discrimination and extraction of PFAS-specific ion signals from HR/AM data, leading to enhanced prioritization and structure annotation for non-targeted PFAS analysis. In total, the application of hybrid Orbitrap HR/AM mass spectrometry provided both the sensitivity and spectral fidelity and coverage to achieve both high-sensitivity quantitative analysis and holistic non-targeted and suspect screening for PFAS measurements in water, using a single platform.

Novel Aspect
A novel approach to quantitative and qualitative ppt PFAS analysis in water on a single analytical platform.