HPLC‐NMR Spectroscopy

The linking of NMR spectroscopy on-line with a separation technique, such as high performance liquid chromatography (HPLC or LC), provides many advantages for the structural characterization of unknowns present in mixtures. In particular, the use of this on-line technology can remove the need for the isolation of the analyte in a pure form, thus improving both speed and efficiency. Technical advances such as the implementation of capillary techniques, cryoflow probes, and on-line sample concentration via solid phase extraction have all contributed to increasing the sensitivity of LC-NMR, thereby making the technique increasingly useful in a range of application areas including pharmaceutical and environmental analysis, natural products research, and studies on drug and xenobiotic metabolism. The combination with on-line mass spectrometry (MS) to provide LC-NMR-MS systems enables even more information to be recovered from samples. Here, the methods employed in LC-NMR, and LC-NMR-MS, for the analysis of chromatographic eluents are described and illustrated with representative applications. Keywords: liquid chromatography; hyphenation; NMR spectroscopy; drug metabolites; natural products