Abstract
Noncovalent complexes were used for structural determination and isomer differentiation of flavonoid glucuronides. Several flavonoid glucuronides including naringenin‐7‐O‐glucuronide, synthesized here for the first time, were used as test compounds. Electrospray ionization quadrupole ion trap mass spectrometry with collision‐induced dissociation (CID) was used to analyze complexes of the form [Co(II) (L‐H) (Aux)]^+^ and [Co(II) (L‐H) (Aux)~2~]^+^, in which L is the flavonoid glucuronide and Aux is a phenanthroline‐based ligand. These complexes yielded characteristic fragmentation patterns that facilitated assignment of the substitution position of the glucuronides. The methods were adapted to liquid chromatography/tandem mass spectrometry (LC‐MS/MS) with postcolumn cobalt complexation and were tested on extracts from biological fluids. The metabolites naringenin‐7‐O‐glucuronide and naringenin‐4′‐O‐glucuronide were detected in human urine following the consumption of grapefruit juice. Isomeric quercetin glucuronides were identified and differentiated after spiking rat plasma at the 1 µM level, proving that the new methods are effective at biologically relevant concentrations. Copyright © 2006 John Wiley & Sons, Ltd.