Determination of the Long-Term Stability of Propofol in Human Plasma Frozen for Eight Years and Quantified by UHPLC-MS/MS.

The intravenous anesthetic propofol is frequently used for the induction and maintenance of general anesthesia. Propofol has, however, a potential for abuse, and it has been involved in suicide deaths particularly among medical personnel. The long-term stability of propofol concentrations in human plasma samples when stored under normal laboratory conditions over several years might be important for forensic toxicology. The present study investigated the long-term stability of propofol after storage at -20°C for eight years. For this purpose, 67 plasma samples from five patients, who had undergone a former clinical trial, were re-analyzed. Plasma samples were extracted using protein precipitation. Propofol plasma concentrations were determined by ultra-performance liquid chromatography (UPLC) with gradient elution, followed by tandem mass spectrometry with electrospray ionization. Deuterium-labeled propofol was used as an internal standard. The assay was linear in the range of 50-10,000 ng/mL with a limit of detection of 0.5 ng/mL and a lower limit of quantification of 50 ng/mL, respectively. Accuracy and precision were high with intra- and interassay errors within ±5%. The median relative deviation between the measurements in 2023 and 2015 was -7.0% (interquartile range: -19.7% and 5.3%). Therefore, propofol concentrations in human plasma can be considered relatively stable in samples frozen at -20°C over eight years, and plasma samples stored under these conditions might be used for forensic purposes.