Identification of a novel imidazole-derived GABA agonist isopropoxate: simultaneous detection and quantification of imidazole-derived analogs from human hairs in abused cases by LC–MS/MS

Distribution and abuse of imidazole-derived γ-aminobutyric acid (GABA) agonists, such as etomidate and metomidate, and their analogs have been encountered frequently especially in China. The aim of this study was to identify etomidate, metomidate, propoxate, and isopropoxate more accurately by establishing a gas chromatography–mass spectrometry (GC–MS) and liquid chromatography tandem mass spectrometry (LC–MS/MS) method and applying it to real forensic cases.

One mg of the seized powder was dissolved in 1 mL of methanol, and subjected to GC–MS and LC–MS/MS. Hair samples were washed and cut into approximately 2 mm sections, then ground to powder by a low-temperature grinder. Twenty mg of the hair powder was extracted with 1 mL of methanol, and the supernatant was subjected to LC–MS/MS.

Etomidate, metomidate, propoxate, and isopropoxate were chromatographically separated and each mass spectrum was obtained by GC–MS. For LC–MS/MS, tested validation data were all satisfactory. The seized powder samples contained isopropoxate, with an approximate content of 30.9%. Etomidate, etomidate acid, metomidate, and isopropoxate could be determined in the submitted hairs, ranging from 2.89 to 8.09 ng/mg, 0.0591–0.177 ng/mg, 0.342–2.77 ng/mg, and 33.2–130 ng/mg, respectively.

Mass spectra and ion chromatograms of etomidate, metomidate, isopropoxate, and propoxate were obtained by GC–MS. We have also established a simultaneous and reliable analytical method for etomidate, etomidate acid, metomidate, and isopropoxate in human hair by LC–MS/MS. This is the first report to present analytical results of a novel imidazole-derived GABA agonist isopropoxate in drug abuse cases.