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Real-Time Detection of Emerging Contaminants with the Vocus B 

Spiro Jorga, Veronika Pospisilova
TOFWERK Switzerland
ACTRIS 2024 Poster

Real-Time Monitoring of Semi-Volatile Emerging Contaminants via Chemical Ionization Mass Spectrometry: Calibration for Comprehensive Atmospheric Analysis of PFAS

This poster presented at the ACTRIS 2024 conference demonstrates the use of time-of-flight chemical ionization mass spectrometry (TOF-CIMS) for the comprehensive atmospheric analysis of PFAS.  

Emerging contaminants encompass an omnipresent, diverse range of chemicals associated with potential risks for human health and the environment. Their measurement in the gas phase traditionally relies on offline sampling technologies providing crucial data for policy makers concerning local or global trends [1]. However, these methods, due to their extended sampling times and thus low time resolution, prove inadequate in pinpointing the atmospheric sources and biggest contributors. Time-of-flight chemical ionization mass spectrometry offers high time resolution measurements with sub-pptv detection limits, allowing direct measurement of trace compounds in the air or headspace. It has been demonstrated as a viable method for real time detection of some of the emerging volatile organic molecules such as PFAS or pesticides [2]. 

In this study, we present measurements of selected emerging contaminants, including PFAS, utilizing our recently developed Aim chemical ionization reactor. Operating at medium pressure (50 mbar), Aim is optimized for adduct-ion chemistry and the measurement of complex, less volatile molecules, which typically undergo fragmentation in other real-time CI techniques like PTR. Additionally, Aim employs a VUV lamp as an ionization source, simplifying safety concerns associated with commonly used radioactive ion sources. We demonstrate the reactor’s ability to achieve extremely sensitive detection for emerging contaminants on the order of sub part-per-trillion range. 

To obtain accurate measurement and determine air concentrations, one must carefully evaluate general steps such as: sample collection, preparation, and calibration. As CIMS involves direct introduction of sample, our focus was on establishing a reliable calibration approach. When dealing with molecules not readily available in standard gas cylinders, calibration involves evaporating a specific volume of a diluted standard solution in a predetermined volume of clean air. We present calibration results that involve comparison of two approaches for standard introduction into the system. 

We report sensitivities to selected compounds and the instrument’s response to changing sample conditions, used solvent and temperature along with an approach that mitigates sensitivity variations based on ambient humidity. Furthermore, we explore the implementation of various reagent ions. 

Figure 1: CIMS calibration curves for selected FTOHs and PFCAs with the corresponding calibration factors. 

Our study emphasizes the reactor’s capability to achieve highly sensitive detection for emerging contaminants at sub ppt levels. The Aim reactor can be used as a versatile tool for ambient measurements, covering various emerging contaminants in addition to the typically measured VOCs and inorganic acids typically monitored by this technique. We will emphasize its potential applications in environmental monitoring. 


[1] Barber, J., L., Berger, U., Chaemfa, C., Huber, S., Jahnke, A., Temme, C., and Jones K., C. (2007) J. Environ. Monit., 9, 530-541 

[2] Riedel, T., Lang, J., R., Strynar, M., J., Lindstrom, A., B. and Offenberg, J., H. (2019) Environ. Sci. Technol. Lett. 6, 5, 289–293 

[3] Murschell, T., Fulgham, S. R., and Farmer, D. K.: (2017) Atmos. Meas. Tech.,10,2117-2127 

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