How to Trace Etomidate in Illegal E-cigarettes from Authentic Human Hair: Identification, Quantification and Multiple-Factor Analysis

The abusive consumption of illegal E-cigarettes containing etomidate (ET) can have a significant impact on public mental and physical well-being. The purpose of this study is to establish a rapid quantitative method using ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC-MS/MS) for the targeted screening of etomidate (ET) and its metabolite etomidate acid (ETA) in hair samples. A 1 mL methanol solution containing the internal standard ET-d5 at a concentration of 50 pg/mg was added to 20 mg of hair and milled below 4 °C. After centrifugation, 5 μL of the supernatant was injected into a UHPLC–MS/MS system. The limit of detection (LOD) and limit of quantification (LOQ) were determined to be 1 pg/mg and 10 pg/mg, respectively, for ET, and 10 pg/mg and 25 pg/mg, respectively, for ETA. Calibration curves for all analytes showed good linearity (r > 0.997), indicating a reliable method. Accuracies were between 92.12