The influence of chemical modifications on the fragmentation behavior of fentanyl and fentanyl-related compounds in electrospray ionization tandem mass spectrometry.

Fentanyl is a synthetic opioid that has been approved by the FDA as a general anesthetic because of its rapid onset and high potency. However, since 2013 an opioid epidemic involving fentanyl or fentanyl-related compounds (FRCs) has swept the United States and caused numerous deaths in every state. The identification of novel FRCs is complicated by the rapid turnover of modifications to the core fentanyl structure. In this study, a series of 16 FRCs were analyzed using electrospray ionization tandem mass spectrometry (ESI-MS/MS) to gain a deeper understanding of the conserved and unique fragmentation behaviors associated with substitution to the core fentanyl structure. This work provides an approach, based on the product ions from ESI-MS/MS, to identify the modification site(s) on the core fentanyl structure for FRCs. Five common locations of substitution to the core fentanyl structure were used to assess the effect of substitution on the fragmentation behavior of FRCs. The proposed fragmentation pathways are supported through the combination of isotopic labeling, multi-stage mass spectrometry (MSn ), and accurate mass measurements with high-resolution mass spectrometry (HRMS). The identification of primary product ions specific to regions of substitution provides an additional tool for the identification of the location of substitution to the core fentanyl structure, which ultimately will assist toxicologists and seized drug analysts in the identification of emerging FRCs.