Abstract
A new approach to combining cross-polarization with multiple-quantum MAS in a two-dimensional NMR experiment is demonstrated, involving cross-polarization from ¹H to the single-quantum coherences of a quadrupolar nucleus. These coherences are then converted directly to multiple-quantum coherences rather than via a population state. In two separate methods, pure-absorption lineshapes are obtained using a z filter and a shifted echo, respectively, with the latter, a "reversed split-t₁" method, demonstrated to be particularly effective. The efficiency of both sequences may be improved by incorporating "fast-amplitude-modulation" (FAM) pulses for both the conversion and excitation of triple-quantum coherences.

Two-dimensional 23Na triple-quantum MAS NMR spectra of dibasic sodium phosphate recorded with a reversed split-t1 pulse sequence. Single- to triple-quantum excitation is performed using (a) a single pulse and (b) a FAM pulse.