From Methods in Polyphenol Analysis

JEAN-LUC WOLFENDER, KARINE NDJOKO AND KURT HOSTETTMANN

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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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...

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:...

The JEOL ECA and ECX NMR spectrometers now support the MRM / Protasis CapNMR. Probe for microscale NMR. "The CapNMR. probe combines recent scientific advances in capillary-scale fluidics and enhanced...

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...