Abstract
T1 relaxation times can be measured at a range of magnetic field strengths by Fast Field-Cycling (FFC) NMR relaxometry to provide T1-dispersion curves. These are valuable tools for the investigation of material properties as they provide information about molecular dynamics non-invasively. However, accessing information at fields below 230 μT (10kHz proton Larmor frequency) requires careful correction of unwanted environmental magnetic fields.In this work a novel method is proposed that compensates for the environmental fields on a FFC-NMR relaxometer and extends the acquisition of Nuclear Magnetic Relaxation Dispersion profiles to 2.3μT (extremely low field region), with direct application in the study of slow molecular motions. Our method is an improvement of an existing technique, reported by Anoardo and Ferrante in 2003, which exploits the non-adiabatic behaviour of the magnetisation in rapidly-varying magnetic fields and makes use of the oscillation of the signal amplitude to estimate the field strength. This increases the accuracy in measuring the environmental fields and allows predicting the optimal correction values by applying simple equations to fit the data acquired. Validation of the method is performed by comparisons with well-known dispersion curves obtained from polymers and benzene.
Highlights
Fast Field-Cycling (FFC) NMR relaxometry is a technique that measures relaxation times over a range of magnetic fields, most commonly the spin-lattice relaxation time T1
The results acquired are presented in curves that indicate the dispersion of T1 values with the applied magnetic field or the corresponding Larmor frequency
These are known as T1-dispersion curves or Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and are used for the investigation of the molecular dynamics of a range of complex systems, with applications in various domains such as oil and polymer science, chemistry, biology or medicine [1,2,3]
Summary
Fast Field-Cycling (FFC) NMR relaxometry is a technique that measures relaxation times over a range of magnetic fields, most commonly the spin-lattice relaxation time T1. The results acquired are presented in curves that indicate the dispersion of T1 values (or alternatively the relaxation rates R1 = 1/T1) with the applied magnetic field or the corresponding Larmor frequency These are known as T1-dispersion curves or Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and are used for the investigation of the molecular dynamics of a range of complex systems, with applications in various domains such as oil and polymer science, chemistry, biology or medicine [1,2,3]. Such a pulse sequence measures the R1 of the sample as a function of the evolution field B0E. This is achieved by repeatedly applying the sequence using identical polarisation and detection stages while varying the duration and field strength of the evolution stage.
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