Use of injection-port derivatization for the analysis of cocaine and its metabolites in urine by gas chromatography–tandem mass spectrometry

Abstract

We developed a fast and reliable method for the analysis of cocaine and three metabolites in human urine, using injection-port derivatization and gas chromatography–tandem mass spectrometry (IPD–GC–MS/MS), with a simplified sample preparation procedure. IPD is an interesting and fast procedure that simplifies sample preparation, where the reaction between the analytes and the derivatization reagent occurs instantly in the heated instrument’s injection port. The IPD eliminates the incubation step required in regular derivatization procedures and leads the analyst exposure to toxic reagents to a minimum. We present a fully validated IPD–GC–MS/MS method to quantify cocaine, ecgonine methyl ester, benzoylecgonine and cocaethylene in urine, using low-sample volume and liquid–liquid extraction (LLE). After sample extraction, cocaine metabolites were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) plus 1% trimethylchlorosilane (TCMS) directly at the injection port of the GC system. Calibration curves were linear over 50–2000 ng/mL, with intra-day and inter-day imprecision values (% RSD) and the analyte concentrations of bias (%) less than 8.8%. Extraction efficiencies greater than 50% were observed for all analytes. All analytes were stable at autosampler conditions (room temperature) for at least 24 h. The method results showed that the developed method has analytical performance enough to be used as confirmation procedure in cocaine exposure verification. To the best of our knowledge, this is the first method to use IPD-GC–MS/MS and silylation reaction in forensic toxicology analysis. The method showed great sensitivity, imprecision and accuracy, using simple and less expensive LLE (compared to solid-phase extraction), with low sample and solvent volumes.