Date of this Version
Journal of Magnetic Resonance, Series B 101, 210-213 (1993)
Pulsed field gradients ( PFG) make it possible to record two-- and three-dimensional spectra using experiments with only a single scan per increment (1-10) . In these experiments PFGs are employed to select the desired coherence-transfer pathway. However, each time a combination of PFGs is used to select a coherence transfer from order -n to m, a second desired pathway, from -n to m , is eliminated, resulting in an intrinsic sensitivity loss of a factor √2. Consequently, coherence pathway selection by means of PFGs is suitable only for applications where the signal-to-noise ratio is not a limiting factor. However, for 3D and 4D experiments applied to dilute protein samples, the intrinsic loss in signal-to-noise of √2 for each PFG coherence selection step is highly undesirable. To circumvent this problem, a different strategy which relies on suppression of undesired coherence-transfer pathways can be used (JI). In this latter approach, coherences associated with spurious magnetization transfer, which frequently result from pulse imperfections, can be eliminated, thereby reducing the number of phase --cycling steps required. A shorter phase cycle allows a reduction in measuring time for experiments that are not limited by the signal-to-noise ratio. Alternatively, it permits an increase in resolution in the indirectly detected dimensions of experiments where measuring time limits the number of increments that can be executed.