SELECTIVE DATA-ACQUISITION IN NMR - THE QUANTIFICATION OF ANTIPHASE SCALAR COUPLINGS

Almost all time-domain NMR experiments employ ''linear sampling,'' in which the NMR response is digitized at equally spaced times, with unif orm signal averaging. Here, the possibilities of nonlinear sampling ar e explored using anti-phase doublets in the indirectly detected dimens ions of multidimensional COSY-type experiments as an example. The Cram er-Rao lower bounds are used to evaluate and optimize experiments in w hich the sampling points, or the extent of signal averaging at each po int, or both, are varied. The optimal nonlinear sampling for the estim ation of the coupling constant J, by model fitting, turns out to invol ve just a few key time points, for example, at the first node (t = 1/J ) of the sin(pi Jt) modulation. Such sparse sampling patterns can be u sed to derive more practical strategies, in which the sampling or the signal averaging is distributed around the most significant time point s. The improvements in the quantification of NMR parameters can be qui te substantial especially when, as is often the case for indirectly de tected dimensions, the total number of samples is limited by the time available. (C) 1996 Academic Press, Inc.