Single-shot measurement of solids and liquids T1 values by a small-angle flip-flop pulse sequence.

ABSTRACT

We propose the small-angle flip-flop (SAFF) pulse sequence as an alternative procedure for the rapid measurement of the 1 H spin-lattice relaxation time in the laboratory frame (T1 ) of solid and liquid substances, in a time-domain NMR experiment. Based on the original flip-flop pulse sequence, this technique allows the fast estimation of T1 values of samples that require minutes to hours of acquisition time if traditional pulse sequences are employed. We have applied SAFF to different substances, with T1 ranging from microseconds up to seconds, including natural clays, polymers, and organic and inorganic solvents. We also demonstrate the potential of the pulse sequence in the real-time monitoring of dynamic processes, such as the conformational changes of polymeric materials during heating. The results we obtained with SAFF are comparable with those acquired with the inversion-recovery pulse sequence, with the addition of several benefits. This pulse sequence obeys steady-state and magnetization-conserving principles, making it possible to dismiss the need for relaxation delay times of the order of 5T1 . SAFF has shown high sensitivity in the resolution of individual components of T1 in multiexponential systems and can be easily integrated to well-established pulse sequences, such as Magic Sandwich Echo and Carr-Purcell-Meiboom-Gill, for the single-shot determination of T1 and T2 or T2* .