Mass spectrometrically detected directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry forthe identification of xenobiotic metabolites in maize plants

Reconstructed ion chromatograms have been used to identify relevant high pe rformance liquid chromatography (HPLC) peaks in a directly coupled high per formance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry (HPLC/NMR/MS) experiment. This has been applied to a study of the metabolism of a model compound, 5-nitropyridone (2-hydroxy-5-nitropyri dine), in maize plants grown hydroponically, By monitoring the on-flow reco nstructed ion chromatogram corresponding to the 5-nitropyridone fragment at m/z 143, and additional molecular ions corresponding to metabolites identi fied as products from similar compounds,(1) relevant peaks were identified rapidly for subsequent stopped-flow H-1 NMR spectroscopic analysis. The com bination of coupled HPLC/NMR/MS enabled the direct identification of three metabolites, namely the N-glucoside, N-malonylglucoside, and O-malonylgluco side. This work demonstrates the power of HPLC/NMR/MS for the structural el ucidation of xenobiotic metabolites in complex biological matrices (such as plant material) with minimal sample preparation. fn particular, using mass spectrometry for the initial identification of relevant HPLC peaks allows the analysis of complex samples without the necessity for other spectroscop ic markers, such as F-19 NMR signal for fluorinated compounds or UV spectro scopy for molecules with strong UV chromophores Copyright (C) 2000 John Whe y & Sons, Ltd.