Trap-and-release membrane inlet ion mobility spectrometry for on-line measurement of trace propofol in exhaled air

Monitoring the exhaled propofol concentration is helpful for anaesthetists to ensure the safety of patients and to adjust the anaesthesia depth. In this study, a trap-and-release membrane inlet ion mobility spectrometer (TRMI-IMS) was constructed for on-line measurement of trace propofol in exhaled air. The effects of trap-and-release parameters such as the trap temperature, release temperature and carrier gas flow rate were investigated. Once optimum experimental parameters were identified, the limits of detection (LODs) for propofol at sampling times of 0.5, 1, 2, and 3 min were found to be 17, 8, 3, and 2 pptv, respectively. With a sampling time of 1 min, the response of TRMI-IMS to propofol was enhanced by a factor of 9 as compared with that of constant temperature MI-IMS; the calibration curve resulting from three individual experiments was linear in the range of 0.1 to 2.5 ppbv. Finally, TRMI-IMS was performed on eleven patients undergoing thyroidectomy surgery to on-line monitor the exhaled propofol. The correlation coefficients (R2) between TRMI-IMS signal intensities and calculated propofol plasma concentrations set in the TCI system were estimated to be in a range of 0.69 to 0.93, demonstrating the potential of TRMI-IMS for on-line predicting the propofol concentration in plasma by exhaled air analysis.