A pulsed field gradient is a short, timed pulse with spatial-dependent field intensity. Any gradient is identified by four characteristics: axis, strength, shape and duration.
Pulsed field gradient (PFG) techniques are key to magnetic resonance imaging, spatially selective spectroscopy and studies of diffusion via diffusion ordered nuclear magnetic resonance spectroscopy (DOSY).[1][2] PFG techniques are widely used as an alternative to phase cycling in modern NMR spectroscopy.
Common field gradients in NMR
The effect of a uniform magnetic field gradient in the z-direction on spin I, is considered to be a rotation around z-axis by an angle = γIGz; where Gz is the gradient magnitude (along the z-direction) and γI is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:
Φ (z,τ) = (γI)(Gz)(τ)
The time duration τ is in the order of milliseconds.
See also
Gradient enhanced NMR spectroscopy
References
Johnson Jr., C. S. (1999). "Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications". Progress in Nuclear Magnetic Resonance Spectroscopy. 34: 203–256. doi:10.1016/S0079-6565(99)00003-5.
Neufeld, R.; Stalke, D. (2015). "Accurate Molecular Weight Determination of Small Molecules via DOSY-NMR by Using External Calibration Curves with Normalized Diffusion Coefficients" (PDF). Chem. Sci. 6: 3354–3364. doi:10.1039/C5SC00670H. PMC 5656982. PMID 29142693. open access
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