Gradient enhanced NMR spectroscopy

Gradient enhanced NMR is a method for obtaining high resolution nuclear magnetic resonance spectra without the need for phase cycling. Gradient methodology is used extensively for two purposes, either rephasing (selection) or dephasing (elimination) of a particular magnetization transfer pathway. It includes the application of magnetic field gradient pulses to select specific coherences. By using actively shielded gradients, a gradient pulse is applied during the evolution period of the selected coherence to dephase the transverse magnetization and another gradient pulse refocuses the desired coherences remaining during the acquisition period.

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Advantages

• Significant reduction in measuring time
• Reduced T1 artifacts
• Elimination of phase cycling and difference methods
• Possibility for three and four-quantum editing
• The ability to detect resonances at the same chemical shift as a strong solvent resonance

Drawbacks

• A need for field-frequency-lock blancking during long runs.

Examples

• Selection of transverse magnetization (I_x, S_x, I_y etc.):

(+)gradient      180°(x)      (+)gradient 

• Suppression of transverse magnetization (I_x, S_x, I_y etc.):

(+)gradient      180°(x)      (-)gradient

References

• Ralpg E. Hurd, Gradient-Enhanced Spectroscopy, Journal of magnetic resonance. 87, 422-428 (1990)