Until recently, most applications of NMR relaxometry involved the study of protons due to the low sensitivity of other nuclei (hetero-nuclei) and to technical difficulties mainly related to signal-to-noise ratio (SNR) problems caused by the low acquisition frequency.
The technique of Fast Field Cycling Relaxometry (FFCR) permits the direct observation of hetero-nuclei with low receptivity and detectability, due to the fact that the magnetic field strength can be switched without the need to vary the frequency of the spectrometer.
FFCR is a low field NMR technique used to measure the spin relaxation curves over a range of B0-fields, spanning about six decades, from about 10-6 Tesla up to ~ 1 Tesla or 3 Tesla, thus information concerning molecular motions characterized by temperature-activated frequencies and described by means of the spectral density J(ω), can be obtained directly.1,2
This multi-nuclear approach expands the potential of FFCR applications and allows exploration of the field dependence of the spin-lattice relaxation time T1 of important hetero-nuclei within substances, especially at low Larmor frequencies (down to 10 1H kHz), where other conventional NMR experiments present severe signal-to-noise (S/N) ratio degradation.
The FFCR technique allows investigation of the content and /or the ability to characterize compounds containing important NMR-sensitive nuclei, such as 2H, 7Li, 13C, 19F, 31P, 23Na. The presence of such nuclei in a limited number of positions can be explored, therefore providing important structural information.
The possibility of measuring nuclear spin relaxation, on nuclei other than 1H, over a wide range of frequencies presents a new advance in the possible applications of TD-NMR and the possibility for new channels of research.
Herein we show the applicability of FFCR for the acquisition of the longitudinal relaxation rate (R1 = 1/T1) as a function of the applied magnetic field strength (NMRD) of some important hetero-nuclei.