Toxicological Analysis of Fluorofentanyl Isomers in Postmortem Blood.

The opioid epidemic continues to evolve in the USA, with fentanyl the most prevalent synthetic opioid in fatal drug overdoses. Following the scheduling of fentanyl's core structure in 2018, there was a notable decline in the prevalence of fentanyl analogs in decedents; however, fluorofentanyl began being reported in casework in the winter of 2020. Fluorofentanyl has three positional isomers (para-fluorofentanyl (p-FF), ortho-fluorofentanyl (o-FF) and meta-fluorofentanyl (m-FF)), with the most predominant isomer that has recently emerged in the USA being p-FF. The goal of this study was to identify p-FF in postmortem cases between October 2020 and April 2021. Urine and blood were extracted using UCT Clean Screen® extraction columns and then screened using an Agilent 1290 Infinity liquid chromatograph (LC) coupled to an Agilent 6545 accurate mass time-of-flight mass spectrometer (TOF-MS) and quantified using an Agilent 6890N GC system coupled with an Agilent 5973 MS. The limit of quantitation (LOQ) for fentanyl, acetyl fentanyl, butyryl fentanyl, p-FF, o-FF and m-FF was 2.5 ng/mL. The screening method could not differentiate the three positional isomers of fluorofentanyl. Suspected overdose cases (n = 370) received from October 2020 through April 2021 from four Medical Examiner Districts in the state of Florida were analyzed for the presence of fluorofentanyl. The LC-QTOF-MS screen yielded 27 decedents positive for fluorofentanyl, with a majority being Caucasian (93%) and male (70%) with ages ranging from 27 to 63 years. Analysis of the blood and urine by GC-MS yielded 14 decedents positive for p-FF, nine of which were positive in the blood. The blood concentrations (n = 9) for p-FF ranged from <LOQ to 30 ng/mL, with an average and median of 9.9 ng/mL and 5.5 ng/mL, respectively. p-FF was identified in the blood of 33% of the cases, and the concentration of p-FF was generally higher than previously reported.