Coherence Selection - Phase Cycling and Gradients

Coherence selection or more correctly the selection of coherence transfer pathways (CT pathways) which contribute to the acquired data is an important part of any pulse sequence. The coherence selection is relevant for 

The methods available for selecting a particular pathway are phase cycling and pulsed field gradients. 

CT pathway selection using phase cycling procedures depends on the signal accumulation of repeated scans. In each scan the same pulse sequence is executed but the phase of the excitation pulses and the receiver is shifted. The coherence selection is based on a difference method such that the unwanted coherences are cancelled because the effect of the phase shift is different for the coherence and the receiver phase. The wanted coherences are constructively added to the detected signal because the coherence and receiver have the same behaviour with respect to the phase shift. The best way to 

It is obvious from Check it 2.3.3.1 that the accumulation of all four scans where the receiver phase is incremented whilst the excitation pulse phase remains constant results in an observed signal with zero intensity. (This may also be confirmed manually in ID WIN-NMR by using the ProcessIFile Algebra command and clicking on the Add./Sub. button in the button panel to add all four FID or spectra together.) However if the phase 

A second example of coherence selection using phase cycling is the suppression of the quaternary carbon signals in a polarization transfer spectrum. DEPT and INEPT type pulse sequences use a polarization transfer step to enhance the signal of an NMR insensitive nucleus such as which exhibits scalar coupling to a NMR sensitive nucleus such as IR. 

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Chapter 9 Coherence selection phase cycling and gradient pulses... 

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