LC-MS/MS determination of the novel fentanyl analog, ortho-methylfentanyl, in drug-related toxicity casework: concentrations in ligated femoral blood.

The purpose of this study was to develop and validate an analytical method to chromatographically separate, identify, and quantify ortho-methylfentanyl (o-methylfentanyl) in postmortem blood. A combination of simple protein precipitation with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was utilized to facilitate chromatographic separation of similar fentanyl analogs, including both meta (m-) and para (p-) methylfentanyl. The analytical range was 1 to 200 ng/mL; the method was validated in accordance with ANSI/ASB Standard 036. In addition to providing details of the validated analytical method, this study details the results of the analysis of 112 case samples (101 postmortem case samples and 11 antemortem case samples) from drug-toxicity related death investigations completed by the toxicology laboratory of the Office of the Chief Medical Examiner, Edmonton, Alberta, Canada. Analytical data is presented which compares concentrations of ortho-methylfentanyl in paired postmortem blood collected from both a visualized, ligated femoral vein together with postmortem blood collected directly from the heart, that is, visualized. Median blood ortho-methylfentanyl concentrations were found to be 5.94 ng/mL (femoral) and 8.04 ng/mL (cardiac). The median cardiac-to-femoral blood concentration ratio across the entire data set was 1.19. The study highlights the varied distribution in the body based on the median concentration of these drugs in postmortem blood.