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. 

Kehr M, Fatkullin N, Kimmich R (2007) Molecular diffusion on a time scale between nano-and milliseconds probed by field-cycling NMR relaxometry of intermolecular dipolar interactions Application to polymer melts. J Chem Phys 126 094903 Kirkwood JG, Riseman J (1948) The intrinsic viscosity and diffusion constant of flexible macromolecules in solution. J Chem Phys 16 565-573 Klein J (1986) Dynamics of entangled linear, branched, and cyclic polymers. Macromolecules 19(1) 105—118... 

The quantum dynamics of proton transfer in the H-bonds of carboxylic acid dimers was also investigated using magnetic field-cycling NMR and optical spectroscopy in the low temperature region, and quasi-elastic neutron scattering at higher temperatures [60, 61]. The interpretation of these results has been done in terms of theoretical methods based on a perturbative instanton approach [61]. 

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... 

Roberts MF, Redfield AG (2004) Phospholipid bilayer surface configuration probed quantitatively by P-31 field-cycling NMR. Proc Natl Acad Sci USA 101 17066-17071... 

Kimmich R, Anoardo E (2004) Field-cycling NMR relaxometry. Prog NMR Spectrosc 44 257-320... 

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... 

M. Vilfan Field-cycling NMR relaxometry of a confined mesogenic fluid. 3rd Conference on Field Cycling NMR Relaxometry, Techniques, Applications, Theories, Torino (2003). 

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