Detection and quantification of 4F-metomidate and its metabolites, metomidate, in human blood and urine by ultraperformance liquid chromatography with triple quadrupole mass spectrometry (UPLC-MS/MS).

PURPOSE: The purpose of this study is to develop and validate a sensitive and specific ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous detection and quantification of 4F-metomidate and its metabolite metomidate in human blood and urine, and to apply this method to authentic specimens obtained from suspected drug abusers. METHODS: A liquid-liquid extraction method was employed for sample preparation, followed by analysis using UPLC-MS/MS. In addition, in vitro human liver microsomes (HLMs) incubation experiments were conducted to confirm the metabolic conversion of 4F-metomidate to metomidate. RESULTS: The developed method exhibited excellent linearity (R2 > 0.9989) within the concentration range of 10-1000 pg/mL for both analytes in blood and urine. The LOD and LLOQ were 5 pg/mL and 10 pg/mL, respectively. Both 4F-metomidate and metomidate were detected in all authentic blood and urine samples from suspected abusers. In the seized e-cigarette liquids, only 4F-metomidate was identified, with no detectable metomidate. HLMs incubation experiments confirmed that 4F-metomidate undergoes metabolic conversion to metomidate in vitro. CONCLUSION: This study presents the first validated UPLC-MS/MS method for the simultaneous quantification of 4F-metomidate and its metabolite metomidate in human blood and urine. The detection of metomidate in biological samples does not necessarily indicate direct intake of metomidate itself, as it may originate from the metabolism of 4F-metomidate or other etomidate analogs. These findings provide a scientific basis for forensic interpretation and highlight the importance of considering metabolic conversion in drug abuse cases.