Determination of trace compounds and artifacts in nitrogen background measurements by proton transfer reaction time‐of‐flight mass spectrometry under dry and humid conditions

Abstract

A qualitative analysis was applied for the determination of trace compounds at the parts per trillion in volume (ppt v ) level in the mass spectra of nitrogen of different qualities (5.0 and 6.0) under dry and humid conditions. This qualitative analysis enabled the classification and discovery of hundreds of new ions (e.g., [S x ]H + species) and artifacts such as parasitic ions and memory effects and their differentiation from real gas impurities. With this analysis, the humidity dependency of all kind of ions in the mass spectrum was determined. Apart from the inorganic artifacts previously discovered, many new organic ions were assigned as instrumental artifacts and new isobaric interferences could be elucidated. From 1140 peaks found in the mass range m/z 0-800, only 660 could be analyzed due to sufficient intensity, from which 463 corresponded to compounds. The number of peaks in nitrogen proton transfer reaction (PTR) spectra was similarly dominated by nonmetallic oxygenated organic compounds (23.5%) and hydrocarbons (24.1%) Regarding only gas impurities, hydrocarbons were the main compound class (50.2%). The highest contribution to the total ion signal for unfiltered nitrogen under dry and humid conditions was from nonmetallic oxygenated compounds. Under dry conditions, nitrogen-containing compounds exhibit the second highest contribution of 89% and 96% for nitrogen 5.0 and 6.0, respectively, whereas under humid conditions, hydrocarbons become the second dominant group with 69% and 86% for nitrogen 5.0 and 6.0, respectively. With the gathered information, a database can be built as a tool for the elucidation of instrumental and intrinsic gas matrix artifacts in PTR mass spectra and, especially in cases, where dilution with inert gases plays a significant role. K E Y W O R D Sgas impurities, gas traces, industrial gases, proton transfer reaction time-of-flight mass spectrometry, volatile organic compounds

Characterization of the new BATCH Teflon chamber and on-line analysis of isomeric multifunctional photooxidation products

“…Especially for small molecules, such artefacts can relate to either isobaric interferences, or the actual formation of the target compounds within the instrument upon fragmentation of larger compounds (Michoud et al, 2018;Salazar Gómez et al, 2021).…”

Emissions and uptake of volatiles by sampling components in breath analysis

“…Other suspected silanes and siloxanes that were quantified here by PTR-TOFMS were not observed in the two mask studies, yet other PTR-MS measurements on TMS have reported that this compound converts to dimethylsilandiol (DMSD; m/z 93.035) in the presence of water vapour, which supports the present observations. A signal detected at m/z 75.034 is likely associated with the loss of a methyl group from TMS, and two dominant signals observed at m/z 147.086 and m/z 149.048 could be attributable to the dehydration of pentamethyldisiloxane and tetramethylcyclodisiloxane, detected at m/z 165.084 and m/z 167.053, respectively [38,39]. Additional emissions of compounds from the mask associated with this chemical class were silicic acid, trimethylsilyl ester (>1 ppb V ) and 1,1,3,3-tetramethyl-2-oxa-1,3disilacyclohexane (<1 ppb V ), as has been reported previously [6,7].…”

A Gas Generating System for Complex Gas Mixtures – Multifunctional Application in PTR Method Optimization and Downstream Methanol Synthesis

“…A significant fragmentation of toluene could also not be observed, meaning that the humidity and the formation of water clusters did not have an influence on the fragmentation pattern, which otherwise could affect the sensitivity. [29] After switching off the injection of toluene as well as the water injection, a signal drop is observed within less than 50 cycles, showing a low memory effect of toluene and water (Fig. S13).…”

“…However, to validate the herein simulated data with real gas mixtures from steel mill emissions, compounds or moreover gas mixtures also have to be remeasured under humid conditions, since only in this way impurities and reasons for the deactivation of catalysts can be detected in detail. [29,42,43] Before analyzing the obtained data, the signal has to be normalized to the obtained values of the reagent ion. Therefore, the ion signal of RH + is normalized to the primary ion (H 3 O + ) signal of 10 6 counts per second (cps) (Eq.…”

“…Further advantages of PTR-MS are that no sample preparation is needed, a higher mass range is available compared to conventional mass spectrometers, a complete mass spectrum is detected within a second and a higher mass resolution and sensitivity is given, which multiplies the analytical information contained in the spectra. [28] Although complex gas mixtures can be analyzed with this technique, it has to be considered that the detection of isomers is not possible and the determination of isobars is extremely challenging depending on mass resolution and additionally, the presence of parasitic ions such as NO + and O þ 2 can enable undesired reactions [29]. The application within this work is to combine PTR-time-of-flight(TOF)-MS with a gas mixing system to identify effects of the composition of gas matrices.…”