Analysis of cis and trans 3-methylfentanyl by liquid chromatography-high resolution mass spectrometry and findings in forensic toxicology casework.

3-methylfentanyl (3-MF), N-(3-methyl-1-phenethyl-4-piperidyl)-N-phenyl-propanamide, has reappeared on the US illicit drug market since its disappearance after a series of overdose deaths in 1988. 3-MF presents an analytical challenge, due to presence of cis and trans stereoisomers, each with different potencies, and ultimately very low concentrations in the blood after use. A method was developed using liquid chromatography-time-of-flight-mass spectrometry for the analysis of (±)-cis-3-MF and (±)-trans-3-MF in blood specimens after solid phase extraction. The linear dynamic range of this method was 0.1-10 ng/mL. Blood samples from 25 postmortem cases and 2 human performance case involving 3-MF were submitted for quantitative analysis. The mean and median concentration for the (±)-cis-3-MF were 0.84 ng/mL (±0.81) and 0.67 ng/mL, respectively, range 0.14-3.43 ng/mL. The resulting (±)-trans-3-MF mean concentration was 0.46 ng/mL (±0.38) and the median concentration was 0.37 ng/mL with a range of 0.11-1.90 ng/mL. The resulting (±)-cis-3-MF and (±)-trans-3-MF concentrations were summed to give the total amount of 3-MF present in the case with the resulting average concentration at 1.28 ng/mL (±1.16), median at 1.01 ng/mL and range 0.18-5.18. As the estimated dose of this compound is approximately 0.1 mg-0.5 mg with the resulting concentrations in the sub-nanogram range, it is necessary for forensic toxicology laboratories to obtain instruments sensitive enough to detect these substances in driving under the influence of drugs and postmortem cases. Quantitation of 3-MF with separation of (±)-cis and (±)-trans-3-MF provides additional detail for more specific toxicological interpretation.