Method development for the analysis of PFAS and neutral precursors in active and passive air samplers

Poly- and perfluoroalkyl substances (PFAS) are a chemical class of global concern because of their persistence, toxicity and widespread presence in the environment. This work aimed to develop a robust and reliable method to analyse perfluorohexane sulfonic acid (PFHxS), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), as well as the neutral volatile PFOS precursors, namely perfluorooctane sulfonamides and perfluorooctane sulfonamidoethanols (FOSAs/FOSEs). Because these compounds can be distributed globally through atmospheric long-range transport, air sampling materials, such as polyurethane foam (PUF) or styrene-divinylbenzene resin (XAD) sorbents are used to capture them. Parameters optimised were extraction solvents, solid phase extraction (SPE) as clean-up and instrumental parameters of the utilised ultra-performance liquid chromatograph tandem mass spectrometer (UPLC-MS/MS) with electron spray ionisation (ESI). The resulting method consisted of Soxhlet extraction with methyl tert-butyl ether (MTBE), and subsequently methanol, followed by a weak anion exchange (WAX) SPE clean-up and injection onto a LC-ESI-MS/MS system, quantification by using isotope dilution. This method was applied for analysis of samples from active (AAS) and passive air samplers (PAS), as well as snow, that were collected in Sweden during the project. Additionally, PUF samples exposed for three months in Örebro in 2017 and several PAS/PUFs spanning two years and sampled as part of the Global Monitoring Plan (GMP), were analysed. The performance of the method was evaluated and gave median recoveries of internal standard of all analytes in blanks of all sample batches ranging from 42 % to 105 %, while median recoveries in real samples were below 20 %. Because of the poor recoveries in samples, only concentrations of ionic PFAS in PAS/PUFs and snow samples from Örebro could be determined. Mean concentrations in PUF samples form Örebro from 2017 were between 30 and 40 pg/m³ and between 6 and 19 pg/m³ for L-PFOS and PFOA, respectively. Lowest concentrations were detected for PFHxS. Concentrations of L-PFOS and PFOA detected in snow in Örebro during the project were roughly one order of magnitude higher compared to the Arctic and about two orders of magnitude lower than in urban China. Overall, more data and a more reliable analytical method is needed to draw conclusions about seasonal or regional variability or correlations between atmospheric PFAS concentrations and wet precipitation. To develop a reliable analytical method for the analysis of PUFs, more real samples need to be available to accurately assess efficiency of clean-ups