Abstract
In the present work we present an investigation of the negative ion-molecule chemistry of the anaesthetics isoflurane, ISOF, and enflurane, ENF, in an ion mobility spectrometry/mass spectrometry (IMS/MS), in both air and nitrogen. Hexachloroethane (HCE) was introduced in both air and nitrogen to produce Cl– as a reactant ion. This study was undertaken owing to uncertainties in the chemical processes, which lead to the cluster ions reported in other work (Eiceman et al. Anal. Chem. 61, 1093–1099, 1). In particular for ISOF the product ion observed was ISOF.Cl–, and it was suggested that the Cl– was formed by dissociative electron attachment (DEA) although there was mention of a chlorine containing contaminant. We show in this study that ISOF and ENF do not produce Cl– in an IMS system either by capture of free electrons or reaction with O2–. This demonstrates that the Cl– containing ions, reported in the earlier study, must have been the result of a chlorine containing contaminant as suggested. The failure of ISOF and ENF to undergo DEA was initially surprising given the high calculated electron affinities, but further calculations showed that this was a result of the large positive vertical attachment energies (VAEs). This experimental work has been supported by electronic structure calculations at the B3LYP level, and is consistent with those obtained in a crossed electron-molecular beam two sector field mass spectrometer. An unusual observation is that the monomer complexes of ISOF and ENF with O2– are relatively unstable compared with the dimer complexes.Graphical ᅟ
Highlights
Isoflurane (ISOF) and enflurane (ENF) are volatile halogenated ethers that are used as anaesthetics in human medicine, their use is starting to decline and being replaced with sevoflurane
ENF and ISOF do not produce Cl– in an IMS system by capture of free electrons or reaction with O2-. This demonstrates that the Cl– containing ions reported in the earlier study were the result of a chlorine containing contaminant as suggested [1]
The failure of ENF and ISOF to undergo dissociative electron attachment (DEA) was initially surprising given the high calculated electron affinities, but further calculations showed that this was a result of the large positive vertical attachment energies (VAEs)
Summary
Isoflurane (ISOF) and enflurane (ENF) are volatile halogenated ethers that are used as anaesthetics in human medicine, their use is starting to decline and being replaced with sevoflurane. The use of ion mobility spectrometry/mass spectrometry (IMS/MS) to detect and monitor ISOF, CF3CHClOCHF2, and ENF, CHF2OCF2CHFCl has been reported previously [1], and a device designed for that purpose has been patented [2]. IMS is a gas-phase analytical instrument used to temporally separate reactant and product ions in a drift tube according to their mobility [9]. The product ions are separated according to their m/z values using quadrupole mass filter and detected using a secondary electron multiplier. For this identification of the m/z values, the B-N grid in the drift tube is kept open in order to maximize ion signal intensity. To obtain ion mobility spectra, the B-N gate is used to pulse reactant and product ions generated in the reaction region into the drift region at a frequency of 25 Hz and a pulse width of 600 μs
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