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

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 T_2* .