ADVERTISEMENT RETURN TO ISSUEPREVComment & ReplyNEXTORIGINAL ARTICLEThis notice is a correctionResponse to Comment to "Electron Driven Reactions in Tetrafluoroethane: Positive and Negative Ions Formation"João Pereira-da-SilvaJoão Pereira-da-SilvaMore by João Pereira-da-Silva, Rodrigo RodriguesRodrigo RodriguesMore by Rodrigo Rodrigues, João RamosJoão RamosMore by João Ramos, Carlos BrígidoCarlos BrígidoMore by Carlos Brígido, Alexandru BotnariAlexandru BotnariMore by Alexandru Botnari, Miguel SilvestreMiguel SilvestreMore by Miguel Silvestre, João AmeixaJoão AmeixaMore by João Ameixahttps://orcid.org/0000-0001-8648-9924, Mónica MendesMónica MendesMore by Mónica Mendes, Fábio ZappaFábio ZappaMore by Fábio Zappa, Stephen J. MullockStephen J. MullockMore by Stephen J. Mullock, João M. M. AraújoJoão M. M. AraújoMore by João M. M. Araújohttps://orcid.org/0000-0002-8648-7539, Márcio T. do N. VarellaMárcio T. do N. VarellaMore by Márcio T. do N. Varellahttps://orcid.org/0000-0002-5812-0342, Lucas M. CornettaLucas M. CornettaMore by Lucas M. Cornetta, and Filipe Ferreira da Silva*Filipe Ferreira da SilvaMore by Filipe Ferreira da Silvahttps://orcid.org/0000-0002-2182-2965Cite this: J. Am. Soc. Mass Spectrom. 2022, 33, 3, 614–615Publication Date (Web):January 28, 2022Publication History Received10 December 2021Accepted19 January 2022Revised2 January 2022Published online28 January 2022Published inissue 2 March 2022https://pubs.acs.org/doi/10.1021/jasms.1c00362https://doi.org/10.1021/jasms.1c00362correctionACS PublicationsCopyright © 2022 American Society for Mass Spectrometry. Published by American Chemical Society. All rights reserved. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views694Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (533 KB) Get e-Alertsclose Get e-Alerts

In the search for alternatives to chlorine-containing gases, tetrafluoroethane, CF3CH2F (R134a), a widely used refrigerant gas, has been recognized as a promising substitute for dichlorodifluoromethane, CCl2F2 (R12). When R12 is replaced by R134a, the global warming potential drops from 8100 to 1430, the ozone depletion potential changes from 1 to 0, and the atmospheric lifetime decreases from 100 to 14 years. Electron interactions in the gas phase play a fundamental role in the atmospheric sciences. Here, we present a detailed study on electron-driven fragmentation pathways of CF3CH2F, in which we have investigated processes induced by both electron ionization and electron attachment. The measurements allow us to report the ion efficiency curves for ion formation in the energy range of 0 up to 25 eV. For positive ion formation, R134a dissociates into a wide assortment of ions, in which CF3+ is observed as the most abundant out of seven ions with a relative intensity above 2%. The results are supported by quantum chemical calculations based on bound state techniques, electron-impact ionization models, and electron-molecule scattering simulations, showing a good agreement. Moreover, the experimental first ionization potential was found at 13.10 ± 0.17 eV and the second at around 14.25 eV. For negative ion formation, C2F3- was detected as the only anion formed, above 8.3 eV. This study demonstrates the role of electrons in the dissociation of R134a, which is relevant for an improvement of the refrigeration processes as well as in atmospheric chemistry and plasma sciences.

The high sensitivity of proton transfer reaction-mass spectrometry (PTR-MS) makes it a suitable analytical tool for detecting trace compounds. Its specificity is primarily determined by the accuracy of identifying the m/ z of the product ions specific to a particular compound. However, specificity can be enhanced by changing the product ions (concentrations and types) through modifying the reduced electric field. For current PTR-MS systems, this is not possible for trace compounds that would only be present in the reaction chamber of a PTR-MS for a short time (seconds). For such circumstances, it is necessary to change the reduce electric field swiftly if specificity enhancements are to be achieved. In this paper we demonstrate such a novel approach, which permits any compound that may only be present in the drift tube for seconds to be thoroughly investigated. Specifically, we have developed hardware and software which permits the reaction region's voltages to be rapidly switched at a frequency of 0.1-5 Hz. We show how this technique can be used to provide a higher confidence in the identification of compounds than is possible by keeping to one reduced electric field value through illustrating the detection of explosives. Although demonstrated for homeland security applications, this new technique has applications in other analytical areas and disciplines where rapid changes in a compound's concentration can occur, for example, in the Earth's atmosphere, plant emissions and in breath. Importantly, this adaptation provides a method for improved selectivity without expensive instrumental changes or the need for high mass resolution instruments.

A radio frequency ion funnel reaction chamber is applied for use with a proton transfer reaction ion trap mass spectrometer (PIT-MS). The improvement in sensitivity over our dc-only drift tube ranged from 7.2 x for isoprene to 65 x for benzene. The ideal settings of the ion funnel are found to be a dc voltage of 60 V, RF voltage of 240 V and a pressure of 1.80 mbar. An experimental and theoretical investigation of the ion funnel is presented. Simulations using SIMION and experimental measurements of the m/z dependent transmission of the ion funnel are performed, as well as simulations of the trajectories of ions and their survival probability. These are used to deduce a greater understanding of the operation of the ion funnel and the sensitivity improvements. The funnel is shown to favor transmission of higher m/z, and to increase sensitivity by a combined effect of focusing and increased effective reaction time. The product ions of an example set of compounds are measured systematically and the reagent ion branching profiles studied and compared to ion trap fragmentations. This represents an important undertaking in the characterization studies of ion funnel technology for use in PTR-MS. (C) 2017 Elsevier B.V. All rights reserved.

A key issue with any analytical system based on mass spectrometry with no initial separation of compounds is to have a high level of confidence in chemical assignment. This is particularly true for areas of security, such as airports, and recent terrorist attacks have highlighted the need for reliable analytical instrumentation. Proton transfer reaction mass spectrometry is a useful technology for these purposes because the chances of false positives are small owing to the use of a mass spectrometric analysis. However, the detection of an ion at a given m/z for an explosive does not guarantee that that explosive is present. There is still some ambiguity associated with any chemical assignment owing to the presence of isobaric compounds and, depending on mass resolution, ions with the same nominal m/z. In this article we describe how for the first time the use of a radio frequency ion-funnel (RFIF) in the reaction region (drift tube) of a proton transfer reaction-time-of-flight-mass spectrometer (PTR-ToF-MS) can be used to enhance specificity by manipulating the ion-molecule chemistry through collisional induced processes. Results for trinitrotoluene, dinitrotoluenes, and nitrotoluenes are presented to demonstrate the advantages of this new RFIF-PTR-ToF-MS for analytical chemical purposes.

A novel thermal desorption unit (TDU) has been developed and specifically designed for the detection of trace quantities of explosives using a proton transfer reaction mass spectrometer (PTR-MS). For the first time details on recovery times and instrumental limits of detection for the screening of explosives with this TDU/PTR-MS system are reported. We demonstrate that traces (nanograms or less) of explosives deposited on swabs are desorbed within less than a second upon insertion into the TDU. For a short period of time (seconds) a concentration "pulse" of an explosive enters the drift (reaction) tube of the PTR-MS. This temporal concentration pulse of material is monitored in real-time by recording the product ion intensities for a given explosive as a function of time. By changing the reduced electric field in the drift tube region of the PTR-MS, we demonstrate how selectivity can be improved. This study demonstrates that the TDU/PTR-MS instrument meets security application criteria in terms of sensitivity, selectivity and recovery times. (C) 2015 Elsevier B.V. All rights reserved.