Liquid chromatography-nuclear magnetic resonance, LC-NMR

Liquid Chromatography Nuclear Magnetic Resonance (LC/NMR) Systems... 

Liquid chromatography-nuclear magnetic resonance (LC-NMR) combines the separating power of LC with the structural elucidation capabilities of NMR. It is now possible to separate and elucidate the structures of components in a mixture on-line using this technique. It is most often used to identify natural products, novel compounds and metabolites. 

R636 K. Kawaguchi, T. Nakano and K. Kimura, How Do You Use Liquid Chromatography-Nuclear Magnetic Resonance (LC-NMR) Effectively for Structural Determinations of Pharmaceutical Impurities and Metabolites ,... 

LC-MS (liquid chromatography-mass detector) and LC-NMR (liquid chromatography-nuclear magnetic resonance spectroscopy). 

Efficient detection and rapid characterisation of natural products play an important role as an analytical support in the word of phytochemists. The identification of a metabolite at the earliest stage of separation is a strategic element for guiding an efficient and selective isolation procedure. In this respect, the role of hyphenated techniques such as high performance liquid chromatography coupled to mass spectrometry (LC/MS) or to nuclear magnetic resonance (LC/NMR) has became of great interest. 

The experimental study of steroidal glycosides of echi-noderms is difficult, as noted in many reviews (Burnell and ApSimon, 1983 Quinn, 1988 Minale, Riccio, and Zollo, 1993). The contemporary technique of combined liquid chromatography, nuclear magnetic resonance, and mass spectrometry (LC-NMR-MS) together with solid-phase extraction (MSPD) has been used to characterize all the constituents of a crude mixture of asterosaponins. Use of this technique led to the identification of the 17 constituents of the asterosaponin fraction of Asterias ruhens from 11 mg of crude mixture, itseF obtained from a sample of 5 g of the sea star (Sandvoss et al., 2001). 

Hyphenated analytical techniques such as LC-MS, which combines liquid chromatography and mass spectrometry, are well-developed laboratory tools that are widely used in the pharmaceutical industry. Eor some compounds, mass spectrometry alone is insufficient for complete structural elucidation of unknown compounds nuclear magnetic resonance spectroscopy (NMR) can help elucidate the structure of these compounds (see Chapter 20). Traditionally, NMR experiments are performed on more or less pure samples, in which the signals of a single component dominate. Therefore, the structural analysis of individual components of complex mixtures is normally time-consuming and less cost-effective. The... 

Capillary column gas chromatography (GC)/mass spectrometry (MS) has also been used to achieve more difficult separations and to perform the structural analysis of molecules, and laboratory automation technologies, including robotics, have become a powerful trend in both analytical chemistry and small molecule synthesis. On the other hand, liquid chromatography (LC)/MS is more suitable for biomedical applications than GC/MS because of the heat sensitivity exhibited by almost all biomolecules. More recent advances in protein studies have resulted from combining various mass spectrometers with a variety of LC methods, and improvements in the sensitivity of nuclear magnetic resonance spectroscopy (NMR) now allow direct connection of this powerful methodology with LC. Finally, the online purification of biomolecules by LC has been achieved with the development of chip electrophoresis (microfluidics). 

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