Breaking the T1 Constraint for Quantitative Measurement in Magic Angle Spinning Solid-State NMR Spectroscopy

Quantitative solid-state NMR experimental schemes that break the conventional T-1 constraint are described. The combination of broad-band homonuclear recoupling techniques and the conventional single pulse or cross-polarization (CP) schemes (referred as QUSP or QUCP) render the long T-1 of low-y spins no longer a constraint for obtaining quantitative NMR spectra. During the mixing time when dipolar recoupling occurs, the nonuniformly CP enhanced or recovered spin magnetization is redistributed under the reintroduced homonuclear dipole-dipole interactions so that uniformly enhanced or recovered magnetization is achieved when the system reaches the quasi-equilibrium state. It is shown that quantitative NMR spectra can be obtained for the recycle delays substantially shorter than the conventionally required 5T(1). In addition, the high efficiency gain can be achieved in QUSP and QUCP experiments with a relatively short recycle delay.