Quantitative Analysis of Fentanyl and Six Fentanyl Analogs in Postmortem Specimens by UHPLC–MS-MS†

Since 2013, opioid-related deaths have increased in Miami-Dade County, FL due to fentanyl and fentanyl analogs in the local heroin supply. From 2014 to 2015, a near 600% increase in fentanyl and fentanyl analog-related deaths was observed, followed by another 200% increase in 2016. In addition to fentanyl, six fentanyl analogs were identified in this time period: β-hydroxythiofentanyl, acetyl fentanyl, furanyl fentanyl, carfentanil, butyryl fentanyl and para-fluoroisobutyryl fentanyl. As a result, an analytical method to quantify these compounds in postmortem biological fluids and tissues using solid-phase extraction with analysis by ultra high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS-MS) was developed and validated. All analytes except carfentanil were linear from 1 to 50 ng/mL with a limit of detection (LOD) of 0.5 ng/mL; carfentanil was linear from 0.2 to 10 ng/mL with a LOD of 0.1 ng/mL. For all analytes, bias was within ±14%, intra- and inter-day precision were ≤5% and extraction efficiency was >87%. Dilution integrity was assessed at 1:1, 1:4 and 1:9 (v/v) ratios; percent error from target was <12% for all analytes. No exogenous interferences were observed. Analytes were stable in preserved whole blood stored at 4°C for 9 months; extracted samples were stable in the refrigerated autosampler (15°C) for up to 72 h. The ability to distinguish the isomer pairs isobutyryl/butyryl fentanyl and p-fluoroisobutyryl/p-fluorobutyryl fentanyl is achieved by this method. The method was applied to 312 cases in which fentanyl and/or fentanyl analogs were previously identified. Postmortem concentrations in blood ranged from <0.2 to 0.73 ng/mL for carfentanil and from 30.6 to 91.7 ng/mL for p-fluoroisobutyryl fentanyl in cases in which these analytes were listed as the sole cause of death.