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% and 110.72%. Intra-day and inter-day precision for all analytes at all concentration levels were below 10.13%. Analyte recoveries ranged from 86.90% to 101.43%, with a matrix effect ranging from -18.55% to -14.93%.

The validated method was successfully used to analyze 105 hair samples from suspected ET users. Of these, 50 tested positive for ET and 43 tested positive for ETA above the LOQ. This demonstrates the effectiveness of the developed UHPLC-MS/MS method in detecting ET and ETA in hair samples, which could be instrumental in addressing the issue of illegal E-cigarette abuse and its impact on public health.