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=CF2]+., 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–CF3 (X=Br,Cl) which, upon collisional activation, rearrange and fragment to CHFX+ via elimination of CF2. 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=CF2]+. and HF elimination, as observed earlier for ionized trichloroethene. In contrast with similar chloro- and fluoro-substituted ethanes, halothane does not react with H3O+ 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 O2-., O2-.(H2O) and O3-., possibly via dissociative electron transfer or nucleophilic substitution. Competing proton transfer was also observed in the reaction with O2-. and, at high halothane pressure, also with O2-.(H2O); at lower pressures the molecular anion M-. was observed instead. The other minor anions of the air plasma, NO2-, N2O2-. and NO3-, were found to be unreactive towards halothane.
Positive and negative ion chemistry of the anesthetic halothane (1-bromo-1-chloro-2,2,2-trifluoroethane) in air plasma at atmospheric pressure
MAROTTA, ESTER;SCORRANO, GIANFRANCO;PARADISI, CRISTINA
2005
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=CF2]+., 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–CF3 (X=Br,Cl) which, upon collisional activation, rearrange and fragment to CHFX+ via elimination of CF2. 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=CF2]+. and HF elimination, as observed earlier for ionized trichloroethene. In contrast with similar chloro- and fluoro-substituted ethanes, halothane does not react with H3O+ 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 O2-., O2-.(H2O) and O3-., possibly via dissociative electron transfer or nucleophilic substitution. Competing proton transfer was also observed in the reaction with O2-. and, at high halothane pressure, also with O2-.(H2O); at lower pressures the molecular anion M-. was observed instead. The other minor anions of the air plasma, NO2-, N2O2-. and NO3-, were found to be unreactive towards halothane.
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