ABSTRACT
Many well-established analytical methods are available to identify organic compounds of synthetic and natural origin and to elucidate unknown structures. Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry are by far the most important. Combining liquid chromatography with nuclear magnetic resonance spectroscopy (LC-NMR) was first proposed in the late 1970s. In continuous-flow mode, the chromatographic system is directly connected to an NMR detection cell which is inside the magnet. The NMR spectra are acquired continuously while the chromatographically separated peaks are flowing through the detection cell. The stopped-flow mode is probably the most versatile and widely employed technique among the direct LC-NMR coupling methods because the spectra are measured under static conditions, the NMR measurement time is not limited by the chromatographic run, and users can control the quality of the NMR spectra during the measurement. Loop storage is another of the direct LC-NMR approaches that can be used to analyze samples containing more than one component of interest.
