Analytical Improvements Using Orbitrap-IRMS to Measure Solutions of Per- and Polyfluoroalkyl Substances (PFAS) for Stable Isotopic Ratios

Orbitrap based Isotope Ratio MS is preferable to classical IRMS techniques for measuring PFAS compounds for a verity of reasons. The powerful new Thermo Scientific™ Orbitrap Exploris™ Isotope Solutions workflow harnesses the combination of electrospray ionization (ESI) and high-resolution accurate mass to enable the detection of isotopologues that were previously inaccessible. ESI allows ionization of PFAS directly from the solution without the necessity of converting it to a gas. ESI also has the advantage of performing “soft” ionization, which produces intact molecular ions. These intact molecules can be fragmented within the Orbitrap mass spectrometer to gain intramolecular information on site specific isotope ratios.

 

Here we present the analytical improvements we have developed specifically for investigating the isotopic composition and structure of PFAS. This including sample introduction to enhance the accuracy and reliability of the isotope ratio analysis, buffers, tuning and optimization of ionization and Orbitrap MS parameters, and focusing on fine-tuning of critical parameters such as AGC target and resolution to achieve optimal performance. We will also explore data acquisition strategies for acquiring high-quality data in isotope analysis, including setting up full scan and fragmentation experiments, and data processing techniques to ensure precise and accurate results.