Metabolite Assignment Considerations & Caveats
• One compound can (and often does) give rise to two or more mass spectral (MS) peaks – but there should only be one HPLC peak per compound,
• Some parent ions fragment too quickly to show up in the MS
• Yield calculations are based on fragment ion abundances and assume that all fragments have been accounted for.
• Some structurally similar metabolites may not be separated under the chromatographic conditions used
• Characteristic fragments convey information about site(s) of oxidation by their presence or absence, but absence of evidence is not proof of absence
• Several isomer assignments are based on the presumed monotonic relationship between HPLC retention time and S+logP