Analysis of Fentanyl in Urine by DLLME–GC-MS

Fentanyl is a synthetic narcotic anesthetic ∼80–100 times more po-tent than morphine. Owing to the potential for its abuse, the drug may be included in a forensic toxicology work-up, which requires fast, precise and accurate measurements. Here, the stability of fentanyl was assessed when stored at three different temperatures (220, 4 and 258C) in synthetic urine. Stability at those three temperatures was demonstrated over 12 weeks upon analysis by gas chromatography– mass spectrometry with a deuterated internal standard (fentanyl-D5) utilizing three different extraction techniques: liquid – liquid extrac-tion (LLE), solid-phase extraction and dispersed liquid–liquid micro-extraction (DLLME). The DLLME method was then optimized before use in the analysis of fentanyl in urine samples obtained from autopsy cases at the El Paso County Coroner’s Office. Accuracy of the DLLME method was assessed by completing spike and recovery studies at three different fortification levels (10, 100 and 250 ng/mL) with ex-cellent recovery (89.9–102.6%). The excellent comparability be-tween DLLME and LLE is demonstrated (Bland–Altman difference plot with a mean difference of 4.9 ng/mL) and the use of this meth-odology in the analysis of forensically relevant samples is discussed