Simultaneous detection and quantification of a novel imidazole-derived GABA agonist isopropoxate and etomidate acid from human urines in abused cases by LC-MS/MS

Summary Introduction Distribution of imidazole-derived GABA agonists, such as etomidate, metomidate and its analogs have been encountered frequently especially in China, along with its abuse cases. Recently, we were enquired to investigate urine samples and dubious powder seized from abuse cases, in which a new etomidate analog isopropoxate was detected. Methods The etomidate analog contained in the seized powder was tried to be identified using gas chromatography-mass spectrometry and by hydrolysis its ester structure to related alcohol under basic reaction environment, as a preliminary analysis for the powder composition. Reference standard were then purchased to identify the compound in suspected powder. For urine samples, after adding the internal standard and acetonitrile to the urine samples followed by vortexing and centrifugation, the supernatant layer was analyzed by LC-MS/MS. Results For LC-MS/MS analysis, the coefficient of determination (r2) values of the calibration curves of etomidate acid and isopropoxate in the urine were more than 0.99; the limits of detection (LODs) for etomidate acid, and isopropoxate was 0.025   ng/mL; the limits of quantification (LOQs) of them was 0.05   ng/mL. Etomidate acid and isopropoxate could be determined from submitted urines. And nine isopropoxate metabolites and their major metabolic pathways were identified. Conclusions In this study, we have established a simultaneous and reliable analytical method for etomidate acid and isopropoxate in human urine by LC-MS/MS, and the method could be applied to authentic cases. It is also the first time that the metabolic pathway of isopropoxate in the human body has been explored.