Susceptibility effects

In summary, it is non-trivial to implement magnetic resonance pulse sequences which allow us to monitor unambiguously the decrease in absolute concentration of reactant species and associated increase in product species, but measures of relative concentrations from which conversion and selectivity are calculated are much easier to obtain. However, if such measurements are to be deemed quantitative the spectra must be free of (or at least corrected for) relaxation time and magnetic susceptibility effects. 

Fig. 16. Single voxel STEAM spectra of the SOL muscle (top) and the TA muscle (bottom). Different fibre orientation in those muscles results in clearly different patterns of the lines in the spectra In SOL (feathered muscle with oblique fibres), IMCL and EMCL signals show lower frequency separation than in TA (spindle-shaped muscle) due to bulk susceptibility effects. Furthermore, in SOL the Cr2 doublet merges into one resonance, the Cr3 triplet is less resolved, and TAU is shifted towards TMA.

J. Furrer, K. Elbayed, M. Bourdonneau, J. Raya, D. Linial, A. Bianco and M. Piotto, Dynamic and magnetic susceptibility effects on the MAS NMR linewidth of a tetrapeptide bound to different resins, Magn. Reson. Chem., 2002, 40, 123-132. 

In the case of spins I—i/l and assuming that the sample does not contain paramagnetic impurities and that other susceptibility effects can also be neglected, the relationship between v g and Vq is given by the following ... 

The T2 relaxation times of 50 /rsec and 40 msec given in the preceding discussion correspond to line half-widths of 6.4 kHz and 8 Hz, respectively. Whipple et al. (265) concluded that the line widths of several hundred Hz which are obtained in practice must be due to bulk magnetic susceptibility effects. This type of line broadening is removable by MAS (273) and they were the first to obtain high resolution spectra with linewidths similar to those expected from the T2 values. 

The room temperature 129Xe spectra of the three carbon blacks are shown in Figure 12.17 and, surprisingly, the line width of these Xe resonances is much smaller than that of Xe in the composites. Although it is known that magnetic impurities and susceptibility effects excessively broaden the 13C line width of carbon blacks, these effects clearly are not as serious for Xe adsorbed at the outer and inner surfaces of the carbon black aggregates [20]. 

The T2 shortening effect induced by paramagnetic substances is known as the susceptibility effect, which in hemorrhages is caused by the presence of either deoxyhemoglobin, or intracellular methemo-... 

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