# Real-Time Identification and Quantification of Per- and Polyfluoroalkyl Substances Using High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometry with Positive Reagent Ions

## TL;DR

This paper introduces a real-time method to detect and measure harmful PFAS chemicals in the air using a high-resolution mass spectrometer.

## Contribution

The study presents the first real-time method for detecting gaseous PFAS using HR-CIMS with positive reagent ions.

## Key findings

- The method achieves detection limits as low as 2 to 40 ppt for various PFAS compounds.
- NO+/O2+ and O2+ reagent ions enable sensitive detection of PFAS via fluoride abstraction, hydride abstraction, or charge transfer.
- The technique is suitable for monitoring PFAS in ambient air and near emission sources.

## Abstract

Per- and polyfluoroalkyl substances (PFAS) are emerging
pollutants
of concern, primarily due to their terminal degradation products,
which exhibit environmental persistence and mobility. Several groups
of PFAS, including hydrofluoroolefins (HFOs), perfluoro olefins (PFOs),
perfluoro vinyl ethers (PVEs), and hydrofluoroalkanes (HF-alkanes),
are volatile and reside predominantly in the gas phase. PFAS such
as HFOs, PFOs, and PVEs are considered reactive and may generate short-chain
degradation products that persist in the environment. Despite the
importance of these gaseous PFAS, there is a lack of analytical techniques
capable of providing high-resolution temporal measurements of potential
precursors to terminal degradation products. This study presents the
first real-time method for detecting and quantifying atmospheric HFOs,
PFOs, PVEs, and HF-alkanes using a high-resolution chemical ionization
mass spectrometer (HR-CIMS). Using NO+ mixed with O2
+ (NO+/O2
+), and
O2
+ as reagent ions, the CIMS was able to identify
and quantify PFAS via fluoride abstraction (M – F)+, hydride abstraction (M – H)+, or charge transfer
(M+) mechanisms. The method achieves 10-s limits of detection
(LOD) ranging from 2 to 40 ppt, enabling online monitoring in ambient
air, especially near emission sources or in indoor environments. The
use of NO+/O2
+ and O2
+ reagent ions with HR-CIMS provides a novel and sensitive
approach for real-time detection of PFAS via positive reagent ion
modes, especially for emerging gas-phase PFAS that currently lack
suitable online measurement techniques to better constrain their atmospheric
emissions and concentrations.