Accurate measurements of self‐diffusion coefficients with benchtop NMR using a QM model‐based approach

Abstract

The measurement of self-diffusion coefficients using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy is a well-established method. Recently, benchtop NMR spectrometers with gradient coils have also been used, which greatly simplify these measurements. However, a disadvantage of benchtop NMR spectrometers is the lower resolution of the acquired NMR signals compared to high-field NMR spectrometers, which requires sophisticated analysis methods. In this work, we use a recently developed quantum mechanical (QM) model-based approach for the estimation of selfdiffusion coefficients from complex benchtop NMR data. With the knowledge of the species present in the mixture, signatures for each species are created and adjusted to the measured NMR signal. With this model-based approach, the self-diffusion coefficients of all species in the mixtures were estimated with a discrepancy of less than 2 % compared to self-diffusion coefficients estimated from high-field NMR data sets of the same mixtures. These results suggest benchtop NMR is a reliable tool for quantitative analysis of self-diffusion coefficients, even in complex mixtures.

Benchtop NMR-Based Metabolomics: First Steps for Biomedical Application

“…Spectral editing techniques have been developed to address the limitations of benchtop NMR spectroscopy, such as limited spectral dispersion leading to signal superpositions and difficulties in compound identification and quantification. Two popular techniques for aiding in identification and quantification are pure shift NMR [ 57 , 58 ] and diffusion-ordered spectroscopy (DOSY) [ 59 , 60 , 61 ]. Pure shift NMR, also known as “chemical shift spectra” or “homonuclear broadband decoupling,” disentangles overlapped proton NMR spectra, with methods such as the 1D projection of 45° tilted 2D J-resolved experiment [ 62 ] and the Zangger-Sterk (ZS) method, based on a low intensity gradient combined with a selective shaped pulse to spatially encode the signal frequency into the tube [ 63 ].…”

Determination of self‐diffusion coefficients in mixtures with benchtop 13C NMR spectroscopy via polarization transfer

“…Another way of tackling this problem is to use mathematical methods such as direct exponential curve resolution algorithm (DECRA), 39 multivariate curve resolution (MCR), 40 speedy component resolution (SCORE) 41 or a QM model-based approach. 42 However, all these methods need additional software packages and expert knowledge to apply the fitting procedure properly on the crowded 1 H NMR spectrum and cannot fully resolve the problems resulting from overlapping peaks. In diffusion-ordered spectroscopy (DOSY) NMR experiments, species in complex mixture are distinguished by correlating the NMR signals with corresponding self-diffusion coefficients via a data inversion process 1,43,44 (note that the acronyms PFG-NMR and DOSY experiments might be used as synonyms to describe the measurement of self-diffusion coefficients 12 ).…”

“…Another way of tackling this problem is to use mathematical methods such as direct exponential curve resolution algorithm (DECRA), 39 multivariate curve resolution (MCR), 40 speedy component resolution (SCORE) 41 or a QM model‐based approach 42 . However, all these methods need additional software packages and expert knowledge to apply the fitting procedure properly on the crowded 1 H NMR spectrum and cannot fully resolve the problems resulting from overlapping peaks.…”