The use of variable-angle spinning (VAS) with cross-polarization (CP)
for quadrupolar nuclei has been evaluated both experimentally and theo
retically. It is known that under normal spinning speeds the best VAS
angle for performing CP is 0-degrees (parallel to the magnetic field).
We show that, with the use of dynamic-angle spinning (DAS) probes, CP
may be done at 0-degrees and detection in a one-dimensional VAS exper
iment may be performed at any angle in a zero-polarized VAS (ZPVAS) ex
periment. Finally, the combination of CP with k = 5 DAS (where the sam
ple is spun first at 0-degrees followed by 63.43-degrees) provides bot
h the highest resolution and the greatest sensitivity under normal con
ditions.