Analysis of Fentanyl in Urine by DLLME–GC-MS

Fentanyl is a synthetic narcotic anesthetic ∼80–100 times more potent 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 (−20, 4 and 25°C) 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 extraction (LLE), solid-phase extraction and dispersed liquid–liquid microextraction (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 excellent recovery (89.9–102.6%). The excellent comparability between DLLME and LLE is demonstrated (Bland–Altman difference plot with a mean difference of 4.9 ng/mL) and the use of this methodology in the analysis of forensically relevant samples is discussed.