Identification and quantification of VOCs by proton transfer reaction time of flight mass spectrometry: An experimental workflow for the optimization of specificity, sensitivity, and accuracy

Abstract

Proton transfer reaction time of flight mass spectrometry (PTR‐ToF‐MS) is a direct injection MS technique, allowing for the sensitive and real‐time detection, identification, and quantification of volatile organic compounds. When aiming to employ PTR‐ToF‐MS for targeted volatile organic compound analysis, some methodological questions must be addressed, such as the need to correctly identify product ions, or evaluating the quantitation accuracy. This work proposes a workflow for PTR‐ToF‐MS method development, addressing the main issues affecting the reliable identification and quantification of target compounds. We determined the fragmentation patterns of 13 selected compounds (aldehydes, fatty acids, phenols). Experiments were conducted under breath‐relevant conditions (100% humid air), and within an extended range of reduced electric field values (E/N = 48–144 Td), obtained by changing drift tube voltage. Reactivity was inspected using H3O+, NO+, and O2 + as primary ions. The results show that a relatively low (<90 Td) E/N often permits to reduce fragmentation enhancing sensitivity and identification capabilities, particularly in the case of aldehydes using NO+, where a 4‐fold increase in sensitivity is obtained by means of drift voltage reduction. We developed a novel calibration methodology, relying on diffusion tubes used as gravimetric standards. For each of the tested compounds, it was possible to define suitable conditions whereby experimental error, defined as difference between gravimetric measurements and calculated concentrations, was 8% or lower.

Endogenous aldehyde accumulation generates genotoxicity and exhaled biomarkers in esophageal adenocarcinoma

“…Drift tube conditions were temperature 110 °C, pressure 2.30 mbar, and voltage 350 V, resulting in an E/N of 84 Td (1 Townsend = 10–17 V cm 2 ). Optimal measurement conditions were chosen based on a validated experimental workflow 47 . Sample inlet flow was set to 40 sccm.…”

Importance of secondary organic aerosol formation of &lt;i&gt;α&lt;/i&gt;-pinene, limonene, and &lt;i&gt;m&lt;/i&gt;-cresol comparing day- and nighttime radical chemistry

“…The examination of the oxidation of atmospherically relevant compounds and the resulting SOA formation is of large importance for a better understanding of atmospheric chemistry and its response to future climate change. Several studies predict an increase in BVOC emissions as a response to a warmer climate (e.g., Sanderson et al, 2003;Lathière et al, 2005;Heald et al, 2008). The increase in monoterpenes emission is estimated to be up to 50 % (Lathière et al, 2005).…”

Analysis of volatile fraction of sweetie (Citrus maxima × Citrus paradisi) and its parent fruit using proton transfer reaction mass spectrometry

“…VOCs were then measured by direct injection of the samples’ headspace into the PTR-TOF-MS drift tube with flow rate of 50.0 cm 3 /min. The operating parameters in the drift tube were set, respectively, at: pressure 2.6 mbar, temperature 70 °C and E / N value of 120.0 Td which allows to avoid excessive formation of water clusters [35]. Ambient air passed through a carbon filter (Supelpure HC, Supelco, Sigma-Aldrich, Steinheim, Germany) was used as carrier gas.…”