From Methods in Polyphenol Analysis


1 Introduction

The coupling of HPLC with nuclear magnetic resonance spectroscopy (LC-NMR) is one of the most powerful methods for the separation and structural elucidation of unknown compounds in mixtures.1 The recent progress in pulse field gradients and solvent suppression, the improvement in probe technology and the construction of high-field magnets have given a new impulse to this technique which has emerged since the mid-1990s as a very efficient method for the on-line identification of organic molecules. LC-NMR thus represents a potentially interesting complementary technique to LC-UV-MS in phytochemical analysis for detailed on-line structural analysis of natural products. Recent applications have demonstrated the usefulness of this technique. 2 7

For the analysis of polyphenols, and especially of flavonoids, xanthones or related compounds, LC-NMR affords useful information on the nature of the polyphenol skeletons and on their substitution patterns. As will be discussed below, the information provided by LC-NMR consists mainly of simple 1H-NMR spectra or 1H- 1H correlation experiments. Access to 13C-NMR information is possible but is restricted only to a very limited number of cases where the concentration of the LC-peak of interest is very important and 13C-NMR data can be deduced indirectly from inverse detection experiments.8 Indeed, due to the low natural abundance of the 13C isotope (1.1%) the sensitivity for direct measurement in the LC-NMR mode is not sufficient. Approaches involving transfer of spin polarisation from immobilised nitroxide radicals, known as 'dynamic nuclear polarisation' have...

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NMR Probes
NMR probes incorporate radio frequency coils that are tuned for use in certain magnetic field strengths and detect specific nuclei. They can be switched out depending on the specific nuclei to be studied or the type of sample to be analyzed.
NMR Spectrometers
NMR (Nuclear Magnetic Resonance) spectrometers are analytical devices that exploit the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained.
ESR/EPR tubes hold samples in ESR or EPR spectrometers. They are thin glass walled tubes, uniformly thick, that produce low background noise.
NMR Tubes

NMR tubes hold samples in NMR spectrometers. They are thin glass walled tubes, uniformly thick and balanced for smooth spinning.

Topics of Interest

CECILE CREN-OLIVE AND CHRISTIAN ROLANDO 1 Introduction The determination of the physical chemistry properties of polyphenols is essential to understand the mechanism by which the polyphenols exert...

In this chapter we bring all the techniques together, which gives us the ability to identify thousands of simple molecules. However, it also brings the problem of putting together data from up to five...

3.4 Nuclear Magnetic Resonance (NMR) Spectroscopy 3.4.1 Instrumentation This technique is at its most useful in organic structure identification and has numerous applications in polymer analysis.

Overview 1H nuclear magnetic resonance spectroscopy tells us about the environment of the hydrogen atoms in a molecule. The technique is based on exactly the same principles as 13C NMR spectroscopy:...

1H NMR spectroscopy tells us very little about the functional groups present in a molecule. We can detect hydrogen atoms on carbonyl groups, on aromatic rings, on double bonds, on triple bonds and on...