Characterization of etomidate and emerging analogs in human hair using UHPLC-MS/MS and confirmation in real forensic cases

Abstract

The regulation of etomidate, a widely used drug for anesthesia induction and short surgical procedures, has led to the emergence of etomidate analogs such as metomidate, propoxate, and isopropoxate. This study introduces and validates a simple, rapid, and cost-effective ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the determination and quantification of etomidate, etomidate acid, metomidate, propoxate, and isopropoxate in human hair. Using a five-minute gradient elution on a Phenomenex Kinetex Biphenyl column, the method achieves low limits of quantification (LOQs), ranging from 5 to 20 pg/mg. Method validation confirms robust linear calibration curves for the target substances in hair samples within the range of LOQs to 1000 pg/mg, with average correlation coefficients (r) all exceeding 0.999. The method also achieves acceptable intra-day and inter-day precision (<15 %) and trueness(bias, −10.9 % to 14.4 %). The matrix effect ranges from 46.9 % to 94.2 %, and the extraction recovery rate ranges from 84.5 % to 105 %. When applied to authentic cases, this method successfully identified 56 positive samples. The concentrations of etomidate, etomidate acid, metomidate, propoxate, and isopropoxate in positive samples ranged from 27 to 1.5 × 10⁵ pg/mg, 21 to 1.5 × 10³ pg/mg, 18 to 8.7 × 10⁴ pg/mg, 25 to 1.6 × 10⁴ pg/mg, and 22 to 5.0 × 10⁵ pg/mg, respectively.