Development of a direct mass-spectrometry approach for the real-time monitoring of PFAS release from cookware and food contact materials

1. Introduction Mass spectrometry (MS) techniques are widely used in the food safety field, thanks to their high versatility and continuous instrumental advancements. One of the most relevant topics is the determination of per- and polyfluorinated alkyl substances (PFASs) in food related samples, being a class of compounds widely used in industry due to their unique chemical attributes such as high thermal and chemical stability, high polarity, and water/lipid resistance. On the other hand, PFASs are long-term persistent compounds and prone to bio-accumulate in the environment, consequently there is a high risk of human exposure to PFASs through the food chain [1]. In 2020 EFSA set a tolerable weekly intake (TWI) of 4.4 ng/kg body weight per week for four of them [1], consequently EU Regulation 2023/915 established maximum concentration of some PFASs (at μg/kg level) in food products [2]. Food contamination can occur not only during the manufacturing process, but can also be caused by migration from food contact materials (FCMs), such as kitchenware. In this context, several anti-stick coatings used for cookware and tableware rely their water- and oil-repellent properties on PFASs, which can be potentially released into food. Currently, there is no harmonized regulation of PFASs in FCMs, however PFASs are gaining increased regulatory attention. Conventional analytical methods for the determination of PFASs are based on liquid chromatography-mass spectrometry technique (LC-MS); despite their excellent analytical performances, LC-MS methods are usually time-consuming, require significant amounts of solvents, and are not suitable for real-time analysis. A promising technique called condensed phase membrane introduction mass spectrometry (CP-MIMS) was recently introduced to fill this gap; it is a direct MS technique that eliminates the need for sample preparation and chromatographic separation. CP-MIMS uses a semi-permeable membrane as the interface between the sample and the mass spectrometer. Only compounds with suitable chemical-physical properties pass through the hollow tubular membrane, within which an ‘acceptor' phase (AP) flows continuously, transporting them to the ion source for MS detection [3], whereas salts and macromolecules are excluded. CP-MIMS is suitable for direct monitoring of dynamic processes in unprocessed matrices. The present work aimed, for the first time, to expand the applicability of CP-MIMS for the determination of PFASs, characterized by high polarity, and real time monitoring of their release from FCMs. 2. Experimental The CP-MIMS system used for this application consists of three parts: the pumping system for the acceptor phase, the CP-MIMS probe and the mass spectrometer. The pumping system was an HPLC Dionex UltiMate 3000 SD series (Thermo Scientific). The CP-MIMS interface was a hand-made probe created in our lab consisting of a modified Viper® Fingertight (Thermo Scientific) having the two ends connected by a PDMS hollow fibre membrane. The mass spectrometer was an LTQ XL MS (Thermo Scientific) with an electrospray (ESI) source operated in negative tandem mass spectrometry (MS/MS), acquiring the signal by product ion scan mode. A magnetic stirrer hotplate was used to control the temperature and the stirring of the sample. Three compounds were investigated: heptafluorobutyric acid (C4-PFAS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), both in water and simulant B (acetic acid 3% w/v). The CP-MIMS output is a chronogram where the time dependent MS signal changes in response to a variation in analyte concentration in the sample. In particular, the signal is first collected with the membrane immersed in methanol (storage solvent); after that, the probe is immersed in the sample (donor phase) containing PFASs. After few seconds the signal increases until reaching a stable intensity (steady state) which is related to the analyte concentration. Signal is collected for some minutes and the probe is extracted, rinsed with water, and stored in methanol. 3. Results Preliminary results will be presented dealing with the development of CP-MIMS methods for PFASs determination. Since CP-MIMS has not yet been applied for PFASs analysis, several preliminary experiments were necessary to define the critical experimental factors and the corresponding domain. Several parameters affect the performance of the method, as AP flow, AP composition, membrane length, sample pH and sample temperature and stirring. An experimental design approach is necessary to find the optimal experimental conditions to maximize signal intensity and stability and minimize noise. In particular, sample pH and AP composition resulted critical factors influencing the PFASs permeation across the membrane. Various AP compositions have been investigated including methanol, methanol with ammonium hydroxide, methanol/ethyl acetate, methanol/heptane, water/acetonitrile, and water/methanol. Best results were obtained with water/methanol, in line with the hydrophilic characteristics of PFAS; this hypothesis was supported by the absence of signal observed in presence of swelling agents like ethyl acetate or heptane, that are useful to boost the response for less hydrophilic compounds. Other experiments were carried out to study AP flow, sample temperature and hydrochloric acid addition to the sample, with the latter parameter strongly improving the response. Based on preliminary experiments described above it was possible to define the following experimental domain: AP flow, 40-70 μl/min; AP composition, 5-25% v/v water in methanol; membrane length, 1-3 cm; hydrochloric acid (38%) in the sample, 0-2 mL; sample temperature, 25-70°C; sample stirring, 200-800 rpm. This experimental domain will be evaluated using a full factorial design of experiments whose analysis are currently ongoing. 4. Conclusions The suitability of CP-MIMS technique was proved for the analysis of C4-PFAS, PFOA, and PFOS, selected as model compounds of the PFASs. After the identification of critical experimental factors and definition of the corresponding domain, the method is currently under optimization using a full factorial design of experiments. The optimized procedure will allow the evaluation of PFASs release from FCMs into food simulant or liquid food matrices, acquiring the signal in real time during migration tests. This strategy will expand the applicability of the CP-MIMS technique and will deepen knowledge about PFASs migration from FCMs. References [1] EFSA Panel on Contaminants in the Food Chain, EFSA Journal., 9 (2020). [2] Commission Regulation (EU) No 2023/915 on maximum levels for certain contaminants in food and repealing Regulation (EC) No 1881/2006, L 119/103. [3] V. Termopoli, M. Piergiovanni, D. Ballabio, V. Consonni, E. C. Muñoz, F. Gosetti, Separations, 10 (2), 2023, 139. Acknowledgements This research was granted by University of Parma through the action Bando di Ateneo 2022 per la ricerca co-funded by MUR-Italian Ministry of Universities and Research - D.M. 737/2021 - PNR - PNRR - NextGenerationEU and the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3 - Call for tender No. 341 of 15/03/2022 of Italian Ministry of University and Research funded by the European Union – NextGenerationEU Award Number: Project code PE0000003, Project title “Research and innovation network on food and nutrition Sustainability, Safety and Security – Working ON Foods” (ONFOODS). This research was granted by University of Parma through the action Bando di Ateneo 2023 per la ricerca.