Real-time monitoring of PFAS using PTR-TOFMS
May 22 2023
Poly- and Perfluoroalkyl Substances (PFAS) have gained significant attention in the field of analytical chemistry due to their widespread presence and potential health risks. Stringent regulations have led to a growing demand for the detection and quantification of these "forever chemicals." Traditional offline methods such as GC and LC are time-consuming and limit the ability to monitor compounds in real-time.
Ionicon has made significant progress in real-time direct-injection PTR-MS studies on PFAS, utilising the PTR-TOF 6000 Proton-Transfer-Reaction Mass Spectrometer. The system offers a mass resolution of approximately 6000 m/Δm and a sensitivity of about 2000 cps/ppbv. Notably, Ionicon's TRU-E/N® ion chemistry eliminates the need for compound-specific calibration during quantification, making it a versatile solution for PFAS analysis.
Perfluorotributylamine (PFTBA), known as the most potent greenhouse gas, was used as a gas standard for determining Limits-of-Detection (LoDs). The dissociative PTR reactions of H3O+ with PFTBA produced a product ion at m/z 413.977 (C8NF16+). The exceptional sensitivity of the PTR-TOF 6000, coupled with Ionicon's hexapole ion guides' broad transmission range and low chemical background in the high mass region, resulted in excellent LoDs: 2.4 pptv after 1 second of integration time and 280 ppqv with 1 minute integration time. Different reagent ions, including NO+ and NH4+, did not generate PFTBA product ions. However, O2+ reagent ions reacted via dissociative charge transfer to produce ions at m/z 501.971 (C9NF20+) and m/z 263.978 (C5NF10+).
In an indoor air study, a petri dish wetted with Perfluorooctanol (FTOH) was used to create an initial air concentration of 6.7 ppbv in an office environment. Over a monitoring period of 48 hours, the FTOH concentration decreased to 50% within 8.8 minutes and to 10% after 25 minutes. Surprisingly, direct sunlight caused an instant concentration increase by a factor of 2.3, while briefly opening the windows after 48 hours resulted in a minor dip in concentration. Even after 63 hours, the FTOH concentration remained significantly higher at 85 pptv compared to the initial background level of 17 pptv.
Simultaneously, perfluorobutanoic acid (PFBA) was released into the indoor air using a wetted petri dish. Unlike FTOH, PFBA concentration dropped to 50% of the initial 676 pptv within 10 minutes and reached 10% after 25 minutes. Even with sun exposure, the PFBA concentration did not show a significant increase.
These findings demonstrate the outstanding performance of Ionicon's PTR-TOF 6000 for real-time quantification of PFAS in air. In addition, a forthcoming study will explore a wider range of PFAS compounds. In cases where enhanced performance is required, Ionicon recommends their new FUSION PTR-TOF 10k instrument, offering 20-40 times higher sensitivity and approximately twice the mass resolution. The Next-Gen PTR-TOF instrument features the novel Fast-SRI ion source for rapid reagent ion switching and the ultra-clean FUSION reaction chamber for LoDs below 200 ppqv. The FUSION PTR-TOF 10k is TRU-E/N certified, ensuring accurate and reliable measurements.
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