Split inversion-recovery experiment by sample shifting

The proper quantitative NMR (qNMR) setup requires efficient relaxation of all active nuclei between scans. To achieve this, the spectroscopist has to know the longitudinal relaxation constant (T1) for each nucleus involved in the experiment and set the interscan delay to at least five times the longest T1. The T1 is most commonly measured using the inversion-recovery method, which is essentially the acquisition of a series of spectra with increasing delay between 180 deg. and 90 deg. pulses. Unfortunately, the inversion-recovery experiment can last hours if a long T1 is expected. In this paper, we show how to perform it faster by employing SWAPE - an apparatus that can shift the sample vertically synchronously to the pulse sequence. In brief, the inversion recovery occurs in the sample parts that are shifted away from the RF coil while other spins in an active volume are excited and measured. This way, the long, passive delays are avoided, and the experiment is shortened several times. We demonstrate its potential on the formic acid sample, a commonly used qNMR reference standard. The resulting T1=12.99 +/- 0.73 s is in good agreement with the one measured using the conventional approach, T1=14.48 +/- 0.82 s, requiring ca. 5.8 times less acquisition time.