High Kinetic Energy Ion Mobility Spectrometry – Mass Spectrometry investigations of four inhalation anaesthetics: isoflurane, enflurane, sevoflurane and desflurane

Here we report the first High Kinetic Energy-Ion Mobility Spectrometry-Mass Spectrometric (HiKE-IMS-MS) investigations involving four fluranes; isoflurane, enflurane, sevoflurane and desflurane. Unlike standard (atmospheric pressure) IMS, HiKE-IMS can detect these compounds in positive ion mode. This is because its low-pressure environment (∼ 14 mbar) and the associated short ion drift times in the HiKE-IMS ensure the reagent ions O₂^+• and H₃O⁺ are present in the reaction region, and these can react with the fluranes by dissociative charge and proton transfer, respectively. However, their ion intensities are very dependent on the value of the reduced electric field (E/N) applied and the humidity of the air in the reaction region of the HiKE-IMS. In this paper we explore the potential use of HiKE-IMS for air quality control and breath analysis of fluranes. To help in the interpretation of the ion mobility spectra, and hence the ion-flurane chemistry occurring in reaction region, a HiKE-IMS was coupled to a Time-of-Flight Mass Spectrometer so that the m/z values of both the reagent and product ions that are contained within the various ion mobility peaks observed could be identified with a high level of confidence. The dependencies of the intensities of these ions as functions of E/N (30–115 Td) and humidity in the reaction region are reported. A number of product ions have been observed only under low humidity conditions (H₂O volume-mixing ratio ∼ 100 ppm_v), including CHF₂⁺ and CHFCl ⁺ for isoflurane and enflurane, CHF₂⁺, CF₃⁺ and C₃H₂F₅O⁺ for desflurane, and CH₃O⁺, CHF₂⁺, C₃H₃F₄O⁺, C₄H₃F₆O⁺ and C₄H₃F₆O⁺(H₂O) for sevoflurane. It is interesting to note that CH₃O⁺, CHF₂⁺, CHFCl⁺ and CF₃⁺ have shorter drift times than that measured for O₂^+•. This is explained by resonant charge transfer reaction processes occurring in the drift region: O₂^+• + O₂ ⇌ O₂^+•.O₂ ⇌ O₂ + O₂^+•.