Initial demonstration of microplasma ionization/Orbitrap mass spectrometry for molecular screening of perfluorinated compounds†

Abstract

The rapid determination of per and polyfluoroalkyl (PFAS) persistent organic pollutants is of growing interest but remains instrumentally challenging. Traditional techniques require some preliminary knowledge of the target species and often time-consuming multistep procedures. Often, the concentration and compositional range of sample contamination is unknown. This is a limitation in investigating the level and fate of a new material's environmental footprint. The liquid sampling – atmospheric pressure glow discharge (LS-APGD) is a microplasma ionization source which provides combined atomic and molecular (CAM) information about analytes. To extend upon the demonstrated applications of the ionization source, the LS-APGD was coupled to an Orbitrap Fourier transform mass spectrometer (FT-MS) to characterize its capabilities towards the analysis of PFAS compounds, including perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonic (PFOS) acid, extending to the perfluoro sulfonamides, acrylates, and telomer alcohols (FTOH). Across the board, these compounds pose incredible analytical challenges regarding the diverse matrices where they are found, their ubiquitous nature (including the laboratory), the lack of a universal ionization method, and the necessity for complex preconcentration/separation prior to MS analysis. The efforts here set the basic characteristics for such analyses, with the caveat that this laboratory is not outfitted for high-sensitivity PFAS analysis, setting up opportunities for more in-depth developments in the future. The mass spectral features for the respective compound types are very uniform, with those of PFOA, PFOS, sulfonamides, and acrylates dominated by their respective M–H (deprotonated) pseudomolecular ions. FTOH compounds were determined by identifying a common characteristic fragmentation pathway. The simplicity of the spectra and high mass resolution/accuracy suggest that determinations might be made without chemical separations. Linear response curves are realized for all species, with limits of detection of 20 pg mL⁻¹ (PFOA) and 310 pg mL⁻¹ (PFOS) obtained, without pre-concentration, for 60 μL infusions. In contrast to the established electrospray ionization (ESI-MS) methods, the CAM/Orbitrap coupling provides species selectivity across the entire breadth of the PFAS compounds and the potential for mixture discrimination without prior chromatographic separation or preconcentration.