MS/MS studies on the selective on-line detection of sesquiterpenes using a Flowing Afterglow-Tandem Mass Spectrometer (FA-TMS)

A Flowing Afterglow-Tandem Mass Spectrometer (FA-TMS) was used to investigate the feasibility of selective on-line detection of a series of seven sesquiterpenes (SQTs). These SQTs were chemically ionized by either H3O+ or NO+ reagent ions in the FA, resulting among others in protonated SQT and SQT molecular ions, respectively. These and other Chemical Ionization (CI) product ions were subsequently subjected to dissociation by collisions with Ar atoms in the collision cell of the tandem mass spectrometer. The fragmentation spectra show similarities with mass spectra obtained for these compounds with other instruments such as a Proton Transfer Reaction-Linear Ion Trap (PTR-LIT), a Proton Transfer Reaction-Mass Spectrometer (PTR-MS), a Triple Quadrupole-Mass Spectrometer (QqQ-MS) and a Selected Ion Flow Tube-Mass Spectrometer (SIFT-MS). Fragmentation of protonated SQT is characterized by fragment ions at the same masses but with different intensities for the individual SQT. Distinction of SQTs is based on well-chosen intensity ratios and collision energies. The fragmentation patterns of SQT molecular ions show specific fragment ion tracers at m/z 119, m/z 162, m/z 137 and m/z 131 for alpha-cedrene, delta-neoclovene, isolongifolene and alpha-humulene, respectively. Consequently, chemical ionization of SQT by NO+, followed by MS/MS of SQT(+) seems to open a way for selective quantification of SQTs in mixtures

Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko

A full-mission analysis of Cl-bearing species in the coma of comet 67P/Churyumov-Gerasimenko has been conducted using data from the Rosetta ROSINA/DFMS mass spectrometer. This contribution will focus on the challenges encountered to relate DFMS data on Cl-bearing species to the neutral abundances at the comet.DFMS was operated in neutral mode, in which electron impact ionizes a fraction of the incoming neutral gas in the ion source. Only ions in a narrow range around a certain commanded mass-over-charge ratio (m/z) pass through the mass analyser at a time and impact on a micro-channel plate (MCP), creating an electron avalanche that is recorded by a Linear Electron Detector Array chip with two rows of 512 pixels each (LEDA A and LEDA B). Data are obtained as Analog-to-Digital Converter (ADC) counts as a function of LEDA pixel number. The instrument scans over a sequence of m/z values.A well-defined approach exists to convert ADC counts as a function of pixel number to the number of ions that were detected on the MCP. However, to relate the number of ions detected this way to the abundance of neutrals in the coma gas, the sensitivity for each neutral needs to be known. The sensitivity for a certain neutral takes into account the total ionization cross section for the neutral and product ion fraction, instrument transmission and secondary electron yield for each product ion. Sensitivities can be determined experimentally by introducing the neutrals in the DFMS instrument copy in the laboratory, but such data are not available for Cl-bearing species and an alternative approach needs to be used. Fortunately, the use of ratios cancels out some of the factors that play a role in the sensitivity. As an example, for the 37Cl/35Cl ratio, total ionization cross sections and product ion fractions can be considered identical. In the case of 37Cl/35Cl, taking into account the sensitivity results in a correction of more than 15%, mainly due to the secondary electron yield.The 37Cl/35Cl ratio does not appear to change appreciably throughout the mission and is compared with known values from other solar system objects. The Cl/HCl ratio obtained with DFMS indicates that there must be at least one additional chlorine-bearing species on the comet next to HCl, CH3Cl and NH4Cl, the identity of which is unknown at this time

Halogens as tracers of protosolar nebula material in comet 67P/Churyumov–Gerasimenko

We report the first in situ detection of halogens in a cometary coma, that of 67P/ChuryumovGerasimenko. Neutral gas mass spectra collected by the European Space Agency’s Rosetta spacecraft during four periods of interest from the first comet encounter up to perihelion indicate that the main halogen-bearing compounds are HF, HCl and HBr. The bulk elemental abundances relative to oxygen are ~8.9 × 10⁻⁵ for F/O, ~1.2 × 10⁻⁴ for Cl/O and ~2.5 × 10⁻⁶ for Br/O, for the volatile fraction of the comet. The cometary isotopic ratios for ³⁷Cl/³⁵Cl and ⁸¹Br/⁷⁹Br match the Solar system values within the error margins. The observations point to an origin of the hydrogen halides in molecular cloud chemistry, with frozen hydrogen halides on dust grains, and a subsequent incorporation into comets as the cloud condensed and the Solar system formed

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Contribution to the development of selective chemical ionization mass spectrometric (CI-MS) techniques for the detection of biogenic volatile organic compounds (BVOCs)

Non-methane biogenic volatile organic compounds (BVOCs) emitted from vegetation constitute about sixty percent of all volatile organic compounds emitted and represent a total worldwide emission of around 1.15 Pg C per year. Plants emit a large variety of BVOCs, dependent on characteristics of both the plant itself and its surroundings. Emitted BVOCs can rapidly react with the main atmospheric oxidants (OH●, O3 and NO3●) and, in the presence of NOX from anthropogenic origin, BVOC oxidation is known to result in harmful oxidation products, such as ozone (O3) and secondary organic aerosol (SOA). In this regard, BVOCs can be classified according to their reactivity in less reactive BVOCs, such as methanol, acetone and acetaldehyde and highly reactive BVOCs, such as isoprene (C5H8), monoterpenes (C10H16, MTs) and sesquiterpenes (C15H24, SQTs). Especially the latter are important SOA precursors and have therefore become a hot topic in the atmospheric science community in recent years. Fast and sensitive measuring techniques that are able to selectively measure BVOCs are required to determine the importance of each individual BVOC in ecological and atmospheric processes. Gas chromatography mass spectrometric (GC-MS) and chemical ionization mass spectrometric (CI-MS) techniques are most frequently used for BVOC measurements and have complementary strengths and weaknesses. GC-MS has an unparalleled selectivity, but has a relatively low temporal resolution and can only be used discontinuously, while CI-MS is an on-line technique with a high temporal resolution, but is less selective. CI-MS techniques use soft ionization of neutral BVOC molecules in the gas phase through fast exothermic ion/molecule reactions with a reagent ion that does not react with the major constituents of air. Except for its reaction with ammonia and water vapor, the hydronium ion (H3O+) fulfills these criteria and typically reacts by non-dissociative proton transfer with many BVOCs (M), resulting in the corresponding characteristic MH+ product ion. Therefore, it is commonly used as reagent ion in the commercially available proton transfer reaction mass spectrometer (PTR-MS) and selected ion flow tube mass spectrometer (SIFTMS) instruments. After ionization, unreacted reagent ions and BVOC product ions are separated according to their mass-to-charge (m/z) ratio and subsequently detected. The unambiguous detection of BVOCs with CI-MS techniques using a certain reagent ion is therefore only possible when the individual ion/BVOC reactions involved result in product ions at different m/z values. Even when the reactions of BVOCs result in product ions at the same m/z value, as is often the case for isomers, more selective detection of BVOCs can be realized by using tandem mass spectrometric (TMS) instrumentation provided the controlled fragmentation of BVOC product ions showing the same m/z result in significantly different fragmentation patterns. The focus of the research presented in this work concerns the detection of isomeric unsaturated alcohols (C5H9OH and C6H11OH), monoterpenes (C10H16), linalool (C10H17OH) and sesquiterpenes (C15H24) using CI-MS techniques through fundamental studies on ion/BVOC reactions in a SIFT instrument and collision-induced dissociation (CID) of specific reagent ion/BVOC product ions in a tandem mass spectrometric (TMS) instrument

Flowing afterglow selected ion flow tube (FA-SIFT) study of ion/molecule reactions in support of the detection of biogenic alcohols by medium-pressure chemical ionization mass spectrometry techniques

This article deals with the validation of and first measurements with a newly constructed flowing afterglow selected ion flow tube (FA-SIFT) instrument. All reactions were studied in He buffer gas at a pressure of 1.43 hPa and a temperature of 298 K. The validation consisted of the study of the gas-phase ion/molecule reactions of methanol and ethanol (M) with the reactant ions H3O+·(H2O)n (n = 0–3), MH+, M2H+, and MH+·H2O and the reactions of MH+ with H2O. Obtained results are compared with available literature data and with calculated collision rate constants. The validated FA-SIFT has subsequently been used to characterize the reactions of the unsaturated biogenic alcohols 2-methyl-3-buten-2-ol, 1-penten-3-ol, cis-3-hexen-1-ol and trans-2-hexen-1-ol (ROH) with H3O+·(H2O)n (n = 0–3) as well as the secondary reactions of the H3O+/ROH product ions with H2O (hydration) and ROH in view of their accurate quantification in ambient air samples with medium-pressure chemical ionization mass spectrometry (CIMS) instrumentation using H3O+ reactant ions. Whereas water elimination following proton transfer was found to be the main mechanism for all H3O+/ROH reactions studied and for the H3O+·H2O/trans-2-hexen-1-ol reaction, all other H3O+·(H2O)n/ROH (n = 1, 2) reactions proceeded by multiple reaction mechanisms. H3O+·(H2O)3 reactions proceeded mainly (C6 alcohols) or exclusively (C5 alcohols) by ligand switching followed by water elimination. Hydration of the H3O+/ROH product ions was observed whenever they contained oxygen. The secondary reactions with ROH were also found to proceed by multiple reaction pathways