Improving the accuracy of pulsed field gradient NMR diffusion experiments: Correction for gradient non-uniformity

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Pulsed field gradient (PFG) Nuclear Magnetic Resonance (NMR) is crucial for determining self-diffusion coefficients.
• Spatial variations in the applied pulsed field gradient introduce systematic errors, affecting measurement accuracy.
• Non-uniform gradients cause deviations from ideal exponential signal decay, leading to inaccurate diffusion coefficients and error estimations.

Purpose of the Study:

• To develop a general and improved method for calibrating NMR diffusion measurements.
• To address and compensate for systematic errors arising from non-uniform pulsed field gradients.
• To enhance the accuracy of self-diffusion coefficient determination in NMR experiments.

Main Methods:

• Mapping the longitudinal variation of pulsed field gradient amplitude and signal strength using PFG echoes with a weak read gradient.
• Constructing a predicted signal decay function for the entire sample based on the mapped gradient variations.
• Parameterizing the signal decay function as an exponential of a power series for accurate fitting.

Main Results:

• The new calibration method effectively accounts for spatial gradient non-uniformities.
• Apparent diffusion coefficients determined using the new method show improved accuracy compared to conventional fitting.
• Comparison of diffusion coefficients obtained with the new calibration against literature values demonstrates its validity.

Conclusions:

• The developed method offers a robust alternative for calibrating NMR diffusion measurements, mitigating systematic errors.
• Accurate mapping of gradient spatial dependence is key to reliable self-diffusion coefficient determination.
• This approach enhances the precision and reliability of PFG NMR diffusion studies across various scientific disciplines.