A selective reagent ion-time-of-flight-mass spectrometric study of the reactions of O

As a part of an ongoing study to determine the concentrations of inhalation anaesthetics in the exhaled breath of patients following surgery, separate investigations are being undertaken to determine which soft chemical ionisation mass spectrometric techniques are most suitable for real-time breath measurements. Towards that goal, we present here details of a selective reagent ion-time-of-flight-mass spectrometer study investigating the reactions of O2+· with isoflurane, enflurane, desflurane, and sevoflurane. Information on the product ions as a function of reduced electric field and the influence of humidity in the drift (reaction) tube is presented. With increasing humidity in the drift tube, secondary product ion-water reactions lead to significant decreases in the intensities of many of the primary product ions, resulting here in a reduced analytical sensitivity for the four fluranes. However, for breath analysis this is found not to be a major issue owing to the high concentrations of inhalation anaesthetics found in exhaled breath even several days after surgery. This is demonstrated in a clinical measurement involving a patient who had undergone an operational procedure, with sevoflurane being used for maintenance of general anaesthesia