Pulsed magnetic field gradients

Figure 7.25 illustrates the power of magnetic field gradient pulses to eliminate unwanted coherences. The double-quantum filtered COSY spec-... 

Figure 7.25 Homoniiclear double-quantum filtered COSY spectrum (400 MHz) of 8-mMangiotensin II in H,0 recorded without phase cycling. Magnetic field gradient pulses have been used to select coherence transfer pathways. (Reprinted from J. Mag. Reson. 87, R. Hurd, 422, copyright (1990), with permission from Academic Press, Inc.)...

Fig. 2.9.7 Hahn spin-echo rf pulse sequence combined with bipolar magnetic field gradient pulses for hydrodynamic-dispersion mapping experiments. The lower left box indicates field-gradient pulses for the attenuation of spin coherences by incoherent displacements while phase shifts due to coherent displacements on the time scale of the experiment are compensated. The box on the right-hand side represents the usual gradient pulses for ordinary two-dimensional imaging. The latter is equivalent to the sequence shown in Figure 2.9.2(a).

Self-Diffusion of Desmopressin and Monoolein by NMR. The self-diffusion coefficient was measured with the NMR diffusion technique using a Bruker MSL 100 spectrometer. Two magnetic field gradient pulses were applied at either side of the 180-degree pulse in a [90x-T-180y-T-echo] spin echo sequence (7,8) (Figure 2). Due to diffusion, the amplitude of a component in the spin-echo spectrum is attenuated according to (7)... 

For the basic PFGE experiment a spin-echo experiment (either the two-pulse Hahn echo sequence, Fig. la, or the three-pulse stimulated echo sequence. Fig. lb) is combined with two magnetic field gradient pulses with duration 8 and separated by the time duration A. The gradient pulses generate a magnetic... 

The PGSE experiment can detect the presence of two or more diffusivities in the species at resonance. The intensity of the spin echo is a function of the duration 8, magnitude G and the time A between the applied magnetic field gradient pulses ... 

Figure 12.4 The pulse scheme of the three-pulse echo sequence to determine Xe diffusion coefficients in polymers and other porous systems. The shaded areas are magnetic field gradient pulses with amplitude g and length 8. The time between the two gradient pulses A determines the time during which the diffusion path length is...

SELECTIVITY ENHANCEMENT USING MAGNETIC FIELD GRADIENT PULSES... 

Fig. 9. (A) Selective excitation and destruction of magnetization using a magnetic field gradient pulse. PGSE sequences used for diffusional attenuation of the solvent signal, based on the Hahn spin-echo sequence (B) and the stimulated-echo sequence (C). In the Hahn spin-echo sequence the magnetization is always subject to spin-spin relaxation. However, in the stimulated-echo sequence the delays can be set such that A is mainly contained in t2 where the relaxation is longitudinal and thus this sequence is preferable for large solute molecules since the condition T2 < usually holds.

Figure 3.2 A magnetic field gradient pulse along the z-axis randomizes the xy components of the spins in the sample ... 

Figure 24.3 Timing of and magnetic field gradient pulses and their effect on the NMR spin echo. ...

To amplify the effects of diffusion, a pair of magnetic field gradient pulses of magnitude G is applied in addition to the small value Gq of steady gradient. According to Stejskal and Tanner, the amplitude of the attenuated spin echo is given by °... 

Figure 7 Pulsed-gradient spin-echo (PGSE) electrophoretic NMR sequence. This ENMR pulse sequence is used to detect electrophoretic mobility during the gated electric field E, which is applied fora time duration 3 equal to the spacing between a pair of magnetic field gradient pulses. Reprinted with permission from Ref. [37], Copyright [2014], AlP Publishing LLC.

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