Identification of isomeric glucuronides by electronic excitation dissociation tandem mass spectrometry

Glucuronidation is a key phase II metabolic pathway for many drugs and xenobiotics. In pharmaceutical research, performing comprehensive structural analysis to differentiate isomeric glucuronides is critical for understanding the metabolism and reactivity of a drug. However, distinguishing glucuronide isomers using collision-induced dissociation (CID) methods has been challenging, since the glucuronyl moiety is typically lost under collision, leaving no information of the glucuronidation linkage. In this study, we introduce a radical-induced fragmentation method known as electronic excitation dissociation (EED) and has demonstrated its ability to characterize glucuronide structures at the MS² level without requiring additional derivatizations. We showed EED can generate extensive MS/MS fragments, including several unique fragments that could be relied on to distinguish isomers. Here, we present our results of successfully applying EED for analysis of three common types of isomeric glucuronides, including acyl-, N-, and O-glucuronides. The LC-EED-MS/MS workflow we introduced has great potential for high-throughput analysis of glucuronide mixtures in metabolite identification.