Multinuclear high-resolution nuclear magnetic resonance spectroscopy

The analysis of lipids is dominated by chromatographic methods such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) and some other physical methods such as thermo analysis. Nuclear magnetic resonance (NMR) spectroscopy covers only a small part of lipid analysis. In most cases it is used for qualitative analysis such as structure elucidation of lipids. Unlike the other methods NMR spectroscopy is coupled with computer technology, and its development is as fast as that of computer software and hardware. In 1991 the Nobel Prize for chemistry was given to Professor Ernst for the development of Fourier Transform NMR spectroscopy (FT-NMR). The capabilities of these methods even for the elucidation of the three-dimensional structures of small molecules up to macromolecules are impressive. 

The related technique of NMR tomography has entered the medical domain, whereas high-resolution NMR spectroscopy allows investigations into the lipid metabolism of animals and human beings in vivo. Other variations of NMR techniques are solid state NMR and NMR imaging for three-dimensional material control. 

But how is the place of NMR spectroscopy defined in lipid analyses The conventional NMR spectroscopist wants to analyse the structure of purified substances the classical analytical chemists have to quantify single components in complex, often natural lipid mixtures. It is a misconception both of the NMR spectroscopists and of the analysts that NMR cannot be used as a quantitative method. On the contrary, NMR spectroscopy is very suitable for quantitative analysis, as will be shown later. 

Natural lipids consist of the elements hydrogen, carbon, phosphorus, nitrogen and oxygen. Some isotope nuclei of these elements can be detected by NMR. The low natural abundance of and prevents the routine application of NMR to these elements without use of labelled substances, but H, and PNMR spectroscopy are used routinely. Many instruments are equipped with a so-called QNP (quattro nuclei probe) for sequential NMR analysis of H, P and without changing hardware. 

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Multinuclear high-resolution nuclear magnetic resonance spectroscopy... 

Among the techniques more frequently used for elucidating cluster structures are crystallographic studies by both single-crystal X-ray and neutron-diffraction techniques, multinuclear high resolution nuclear magnetic resonance (NMR), and infrared spectroscopy. 

Azo dyes of the common formula X—N=N—Y represent a very important class of dyestuffs,1 with more than 50% of commercial dyestuffs based on this type of compound. Nuclear magnetic resonance (NMR) spectroscopy, especially in its multinuclear form, is a powerful technique for the characterization of such compounds and also for the description of azo-hydrazone tautomerism, a property which is indivisibly linked with this group of dyes. This chapter reports on high-resolution lH, 13C, 14N, 15N, nO, 19F and 31P NMR spectra of azo dyestuffs measured in solutions. 

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