The application of magnetic field gradients in high resolution NMR spectroscopy is well established, and the power of these to increase the speed of acquisition, to improve the level of solvent suppression and to increase the dynamic range of the resonance of interest are well proven. Gradient methods fall into two categories, (1) dephasing, such as crusher gradients in NOESY or heteronuclear experiments, which render unwanted coherences unobservable, and (2) coherence selection gradient echoes, such as in homonuclear multiple quantum filters and heteronuclear pathway selection, in which only the coherences that follow a specific pathway are refocussed. We have introduced a new class of pathway selective gradient experiments, where the evolution due to the magnetic field gradient is employed to discretely spatially modulate the pulse sequence that is seen by the spins. This approach of discretely modulating the spin dynamics over space combines the high dynamic range and artifact suppression of gradient methods with the optimal sensitivity of phase cycling methods; In particular, it avoids the loss in sensitivity of phase cycling methods.
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