LAUSR

This study uses a combination of multi-stage mass spectrometry (MSn ), accurate mass measurements-with high-resolution mass spectrometry (HRMS)-and isotopic labeling to characterize the fragmentation behavior of fentanyl and 4-ANPP. By understanding the fragmentation behavior of fentanyl and its analogs in more detail, toxicologists and seized drug analysts will be better poised to identify new and emerging fentalogs, which are increasingly common and deadly adulterants in the growing opioid crisis. Throughout literature the product ion at m/z 188 is often the most abundant fragment in the mass spectrometric analysis of fentanyl and fentanyl analogs, and this fragment is used for both qualitative and quantitative determinations. Our work shows there are at least three different structures for the isobaric fentanyl product ions at m/z 188, and they each form and fragment via different pathways. The development of fragmentation mechanisms to explain the observed fragmentation pathways of fentanyl and its main precursor 4-ANPP helps contribute to the advancement of knowledge about fentanyl fragmentation and could provide important information for the identification of future fentanyl analogs.