Rapid determination of etomidate and its structural analogues in e-liquid by probe electrospray ionization quadrupole time-of-flight mass spectrometry.

Etomidate and its structural analogues, which have anesthetic effects, are classified as controlled psychotropic drugs. Electronic cigarettes (e-cigarettes) have become more and more popular. With the increase of adding etomidate and its analogues to electronic liquids (e-liquids), there is a trend of abuse, which is a tough problem urgently need to be solved. This seriously affects the health and security of the public and the development of society. A simple, rapid and effective screening method is very crucial for their identification. In this study, we applied a newly developed method, probe electrospray ionization quadrupole time-of-flight mass spectrometry (PESI-QTOF-MS) with DPiMS QT ion source to analyze etomidate and its analogues in e-liquids. It allowed identification in 0.3 min with lower sample usage. Isomers can be distinguished by ion abundance ratios at collision energy (CE) 15 eV, which provided possibility for distinguishing more isomers by in-situ mass spectrometry. Limit of detection (LOD) and limit of quantitation (LOQ) of four substances were 20 ng/mL and 50 ng/mL, respectively. Good linear relationships were obtained in the concentration range of 50-5000 ng/mL with little matrix effect. The accuracy, precision, dilution effect and carryover of the method were also validated. Positive specimens (n = 38) were analyzed by both PESI-QTOF-MS and gas chromatography-mass spectrometry (GC-MS). There were five impurities including nicotine, cooling agent and flavorings were investigated by PESI-QTOF-MS, which provided the possibility for tracing the origin of illegal e-liquids. This study will help solve the backlog of cases and improve work efficiency effectively by reducing analysis time. Furthermore, it meets the need of addressing current situation of drug control and can assist forensic laboratories in investigating cases. It also demonstrates the application prospects of rapid screening in new drugs.