Mass directed peak selection, an efficient method of drug metabolite identification using directly coupled liquid chromatography–mass spectrometry–nuclear magnetic resonance spectroscopy

Mass spectrometry (both MS and MS–MS) has been used to determine which eluting chromatography peaks in an LC–MS–nuclear magnetic resonance (NMR) experiment should be selected for extended NMR spectroscopic measurement. This mass directed selection of chromatographic peaks has been applied to test mixtures and urine samples for identification of drug metabolites. It was used to simultaneously determine when drug-related material was eluting and provided molecular mass information on these components. Stop-flow LC–NMR was used to acquire data for structural characterisation of drug-related components. This work further serves to demonstrate the potential of coupling tandem mass spectrometry using an ion trap spectrometer with LC–NMR spectroscopy, to provide an extremely powerful tool in structural elucidation.