Positive and negative ion chemistry of the anesthetic halothane (1‐bromo‐1‐chloro‐2,2,2‐trifluoroethane) in air plasma at atmospheric pressure

Abstract

The ion chemistry of 1-bromo-1-chloro-2,2,2-trifluoroethane (the common anesthetic halothane) in air plasma at atmospheric pressure was investigated by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The major positive ion observed at low declustering (API interface) energies is the ionized dimer, M(+.)M, an unexpectedly abundant species which possibly is stabilized by two H-bonding interactions. At higher energies [M--HF](+.) and [M--Br](+) prevail; the former, corresponding to ionized olefin [ClBrC=CF(2)](+.), appears to originate from M(+.)M and is quite stable towards fragmentation. The latter fragment ion ([M--Br](+)) and its analogue, [M--Cl](+), which is also observed though at much lower abundance, are originally ethyl cations (+)CHX--CF(3) (X = Br, Cl) which, upon collisional activation, rearrange and fragment to CHFX(+) via elimination of CF(2). All of the above described ions are also observed in humid air: in addition, the oxygenated ion [ClBrC=CFOH](+.) also forms in humid air via water addition to [ClBrC=CF(2)](+.) and HF elimination, as observed earlier for ionized trichloroethene. In contrast with similar chloro- and fluoro-substituted ethanes, halothane does not react with H(3)O(+) in the APCI plasma, a result confirmed by selected ion APCI triple-quadrupole (TQ) experiments. Major negative ions formed from halothane in the air plasma are Br(-) and, to a lesser extent, Cl(-), and their complexes with neutral halothane. APCI-TQ experiments indicated that Br(-) and Cl(-) are formed via reaction of halothane with O(2) (-.), O(2) (-.)(H(2)O) and O(3) (-.), possibly via dissociative electron transfer or nucleophilic substitution. Competing proton transfer was also observed in the reaction with O(2) (-.) and, at high halothane pressure, also with O(2) (-.)(H(2)O); at lower pressures the molecular anion M(-.) was observed instead. The other minor anions of the air plasma, NO(2) (-), N(2)O(2) (-.) and NO(3) (-), were found to be unreactive towards halothane.

Gas‐phase positive ion chemistry of 1‐bromo‐1‐chloro‐2,2,2‐trifluoroethane (halothane) upon electron ionization within an ion trap mass spectrometer

“…Notably, halothane does not react with H 3 O + except to form complexes, thus suggesting that its proton affinity (PA) is <691 kJ·mol −1 4. These observations were confirmed and substantiated by a recent study of the ionic reactivity of halothane in air plasma at atmospheric pressure 5. An interesting ionic product was detected under these high‐pressure conditions, that was attributed to an HF elimination reaction from the ionized molecular dimer M + .…”

“…This compound was the subject of a case study to monitor the effects of bromine on stratospheric ozone, and comprehensive kinetic and product studies were conducted to determine its atmospheric destruction rate and the mechanism of its oxidation 2. In addition to the radical reactivity2 and the photodissociation3 properties, also the gas‐phase ionic reactivity of halothane has become the focus of recent research 4, 5. Thus, the reactions of halothane with atmospheric ions, including H 3 O + and O, were investigated using the SIFT technique;4 these studies revealed a remarkably low reactivity of halothane as compared with, for example, that of related fluoro‐, chloro‐ and fluorochloroethanes.…”

“…An interesting ionic product was detected under these high‐pressure conditions, that was attributed to an HF elimination reaction from the ionized molecular dimer M + . M of halothane 5 …”

Novel CFCs-substitutes recommended by EPA (hydrofluorocarbon-245fa and hydrofluoroether-7100): Ion chemistry in air plasma and reactions with atmospheric ions

“…Specifically, novel nonthermal plasma-based technologies are currently being developed for the removal of VOCs (volatile organic compounds) from contaminated air [2]. A major focus of our research in this field deals with the ionic reactions occurring in such air plasmas, which can be conveniently produced by corona discharges at atmospheric pressure, and investigated by means of APCI-MS analysis [3][4][5][6][7]. Finally, it is worth mentioning that the interest in such novel plasma-based treatment processes is also attributable to the possibility of abatement of ozone-safe compounds which are, however, implicated as greenhouse gases.…”

Reactive desorption electrospray ionization mass spectrometry (DESI-MS) of natural products of a marine alga

“…1). Declustering of such dimers by in-source CID could lead to an increase in the abundance of the deprotonated monomer thus improving the sensitivity for the detection of bromophycolides [45, 46]. In-source CID experiments were performed by varying the direct current (DC) voltage offset of the ion source ion transfer octopole between 0 and 60 V. This resulted in an overall decrease in the signal intensity of the deprotonated bromophycolide A dimer and only a slight increase in the intensity of the deprotonated monomer ion, with a maximum at 40 V. Higher voltages resulted in the concomitant formation of the fragment at m / z 583 (Figure S-2).…”