Pulsed field gradient

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 = γ_IGz; where Gz is the gradient magnitude (along the z-direction) and γ_I is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:

Φ (z,τ) = (γ_I)(Gz)(τ)

The time duration τ is in the order of milliseconds.

See also

• Gradient enhanced NMR spectroscopy

References

1. Johnson Jr., C. S. (1999). "Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications". Progress in Nuclear Magnetic Resonance Spectroscopy. 34 (3–4): 203–256. doi:10.1016/S0079-6565(99)00003-5.
2. 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 (6): 3354–3364. doi:10.1039/C5SC00670H. PMC 5656982. PMID 29142693.