Common metabolic pathways often give rise to multiple instances of isobaric metabolites such as, (but not limited to), multiple mono-hydroxylations and di-hydroxylations with and without phase II conjugations, such as glucuronidation. LC-MS analysis of metabolic pathways for drugs requires accurate detection and identification of closely eluting species with similar RT’s and spectral profiles. This is further complicated by shifting abundance profiles at different time points, species differences and RT shifts due to biological matrix effects. Modern chromatography (and mass spectrometry) is sufficient in many cases, however isobaric species remain problematic. Ensuring closely eluting species have not shifted by RT requires standard addition or commixing of matrix and true isobaric coelutions may go undetected with conventional LC-MS approaches as they rely solely on discrimination using precursor mass. Furthermore, the MS/MS patterns from related compounds are often extremely similar and coelutions give rise to complex spectra which can hinder identification and structural elucidation. MS/MS of metabolites at low concentrations may also introduce noise from matrix at high concentrations. Review this poster to find out more information.