Development of an LC–MS/MS method for the determination of five psychoactive drugs in postmortem urine by optimization of enzymatic hydrolysis of glucuronide conjugates

Abstract

Abstract Purpose Toxicological analyses of biological samples play important roles in forensic and clinical investigations. Ingested drugs are excreted in urine as conjugates with endogenous substances such as glucuronic acid; hydrolyzing these conjugates improves the determination of target drugs by liquid chromatography–tandem mass spectrometry (LC–MS/MS). In this study, we sought to improve the enzymatic hydrolysis of glucuronide conjugates of five psychoactive drugs (11-nor-9-carboxy-Δ9-tetrahydrocannabinol, oxazepam, lorazepam, temazepam, and amitriptyline). Methods The efficiency of enzymatic hydrolysis of glucuronide conjugates in urine was optimized by varying temperature, enzyme volume, and reaction time. The hydrolysis was performed directly on extraction columns. This analysis method using LC–MS/MS was applied to forensic autopsy samples after thorough validation. Results We found that the recombinant β-glucuronidase B-One® quantitatively hydrolyzed these conjugates within 3 min at room temperature directly on extraction columns. This on-column method saved time and eliminated the loss of valuable samples during transfer to the extraction column. LC–MS/MS-based calibration curves processed with this method showed good linearity, with r2 values exceeding 0.998. The intra- and inter-day accuracies and precisions of the method were 93.0–109.7% and 0.8–8.8%, respectively. The recovery efficiencies were in the range of 56.1–104.5%. Matrix effects were between 78.9 and 126.9%. Conclusions We have established an LC–MS/MS method for five psychoactive drugs in urine after enzymatic hydrolysis of glucuronide conjugates directly on extraction columns. The method was successfully applied to forensic autopsy samples. The established method will have broad applications, including forensic and clinical toxicological investigations.