Fast field-cycling NMR

E. Anoardo, G. Galli, G. Ferrante 2001, (Fast-field-cycling NMR Applications and instrumentation), Appl. Magn. Re-son. 20, 365. 

Belton, P.S. and Wang, Y. 2001. Fast field cycling NMR Applications to foods. In Magnetic Resonance in Food Science A View to the Future (G.A. Webb, P.S. Belton, A.M. Gil, and I. Delgadillo, eds), pp. 145-156. Royal Society of Chemistry, Cambridge, UK. 

The instruments currently produced by Stelar prove that Fast-field-cycling NMR relaxometry instrumentation is industrially viable in the sense that (i) its specifications are reasonably reproducible and (ii) once installed, the reliability of the instruments is comparable to that of any other NMR equipment. The overall performance, unthinkable-of only a few years ago, is best witnessed by the examples shown in Fig. 29. 

NEW METHODS FOR FOOD ANALYSIS 6.1. Fast field cycling NMR... 

Whatever model is used, the problem with equation (1) is that it is intrinsically underdetermined since it contains the product of interaction and spectral density terms. The usual solution is to examine relaxation at different temperatures and assume a function (usually exponential) for the temperature dependence of the correlation times. This is problematic in foods, as the structure of food is typically very temperature dependent. The alternative is directly to determine the spectral density function of the material by determining 7, over a wide range of frequencies. This may be done by using fast field cycling NMR. 

A fast field cycling NMR spectrometer is similar to a normal spectrometer, with the exception that the magnetic field may be switched between different fields on the timescale of milliseconds. Further details are given elsewhere.372 Typically, the range of frequencies covered is from about 10 kHz to 10 MHz. A simulation of the behaviour of a spin system obeying BPP theory is given in... 

The preceding sections have shown that fast field-cycling NMR is not restricted to frequency dependent relaxation studies, as often believed. Although the four new kinds of applications illustrated are typical for the basic procedures, it should be pointed out that the method has already been applied in other directions, and so resulted in new growing fields of research in the recent NMR literature. Readers may encounter various headlines intimately related to FC techniques, which however is not always clearly seen or described, for instance zero-field NMR, , cross-relaxation... 

Noack F, Notter M and Weiss W (1988) Relaxation dispersion and zero-field spectroscopy of thermotropic and lyotropic liquid crystals by fast field-cycling NMR, Liquid Crystals 3 907. 

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