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Positive and negative ion chemistry of the anesthetic halothane (1‐bromo‐1‐chloro‐2,2,2‐trifluoroethane) in air plasma at atmospheric pressure
Author(s) -
Marotta Ester,
Bosa Elisabetta,
Scorrano Gianfranco,
Paradisi Cristina
Publication year - 2005
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1794
Subject(s) - chemistry , atmospheric pressure chemical ionization , halothane , ion , atmospheric pressure , ionization , dimer , fragmentation (computing) , mass spectrometry , chemical ionization , analytical chemistry (journal) , polyatomic ion , chromatography , organic chemistry , oceanography , computer science , geology , operating system
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 [MHF] + . and [MBr] + prevail; the former, corresponding to ionized olefin [ClBrCCF 2 ] + . , appears to originate from M + . M and is quite stable towards fragmentation. The latter fragment ion ([MBr] + ) and its analogue, [MCl] + , which is also observed though at much lower abundance, are originally ethyl cations + CHXCF 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 [ClBrCCFOH] + . also forms in humid air via water addition to [ClBrCCF 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. Copyright © 2005 John Wiley & Sons, Ltd.