Analysis and implications of transition-band signals in high-resolution NMR.

The problem of signals generated in and received from regions outside the active coil area is discussed in the context of using standard measurement techniques. Some of the conceptual and practical consequences of the existence of such transition-band signals are highlighted. Examples include radiation damping, pulse-width calibration, lineshape and radiofrequency homogeneity tests, improper saturation, and exchange- and relaxation-rate determinations. One interesting implication is that apparent sample-to-sample variations in the calibrated 90 degrees pulse width values are a function not only of probe tuning and bulk susceptibility effects, but also of the linewidths involved. A semi-quantitative treatment of the phenomenon is also given. Copyright 1998 Academic Press.