Maximizing the sensitivity in 13C cross-polarization magic-angle-spinning solid-state NMR measurements with flip-back pulses.

ABSTRACT

The flip-back pulse combined with cross-polarization magic-angle spinning (CPMAS-FB) has been widely used to reduce the optimal repetition delay, resulting in enhancing sensitivity per unit time. Despite its common use in samples with long 1H T1 relaxation time, the experimental setup of the repetition delay in CPMAS-FB is not obvious. In this article, a simple model is used to derive the optimal repetition delay and expected sensitivity gain through the 1H T1 relaxation time and signal decay during 1H spinlock.