directly, if all nuclei are correlated to the same nucleus (16) or the the same multiquantum
coherence (14, 15), conditions which are not easily fulfilled for most samples.
In a recent publication we presented an approach towards high resolution ex-situ NMR
spectroscopy (19) that is based on nutation echoes (9, 10, 20) due to rf field gradients which
are perpendicular to the static field Bo and proportional to the static field gradient. For sample
regions where the static field and the rf field (B1) gradient are matched, or where the effective
rf gradient can be matched to the static field by appropriate composite pulses, the line-
broadening caused by Bo inhomogeneities can be refocused during the acquisition period by
applying a train of rf gradient pulses (see below). These B1 gradient pulses do not refocus the
evolution of the magnetization under the effect of intrinsic fields due to chemical shift and
indirect couplings, and thus the full spectroscopic information is recovered. In this
contribution we extend this method towards depth sensitive NMR spectroscopy and highly
resolved two-dimensional homo- and    heteronuclear correlation  spectroscopy  using
polarization transfer (INEPT).
THEORY
Nutation echoes
If the gradients of the static magnetic field, Go, and the effective radiofrequency field,
G1, are parallel and their magnitudes are proportional, such that Gi(r) =k-Go(r) over a certain
region of the sample, a nutation echo can be produced by a single radiofrequency pulse: The
rf gradient pulse spreads the magnetization in the yz-plane. During the following time interval
t the transverse component of the magnetization evolves under the influence of the magnetic
field gradient Awoo(r), and the chemical shift, Q (Eq. [1]).

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