Applications of pulsed field gradient techniques and slice selective methods in NMR spectroscopy
Date
2022
Authors
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Publisher
University of Delaware
Abstract
Slice selection NMR spectroscopy is a method that enables the chemical analysis of specific, selected regions of an NMR sample along the z-axis. This type of NMR spectroscopy has applications in metabolomics, kinetics, extractions analyses, and more. The focus of this work is the development of a novel slice selection experiment, called the one-shot double-slice experiment. This experiment enables the simultaneous analysis of two different regions within an NMR tube, with the ability to differentiate between the selected regions, due to the signals from each region being of opposite phase in the resulting NMR spectrum. Slice selection NMR is possible through the combination of pulsed field gradients and shaped pulses. In order to develop this methodology and novel experiment, it was first necessary to develop a deep understanding of those two fundamental components. Pulsed field gradients were investigated through diffusion NMR spectroscopy and one-dimensional NMR imaging. The diffusion experiments were conducted to determine the self-diffusion coefficients of surfactant at various concentrations, in order to further define the system beyond the critical micelle concentration (at which point surface tension no longer can provide insight as to changes in the system). The one-dimensional gradient imaging experiments were employed to determine the location of the receiver coil with respect to the interface of biphasic NMR samples, in order to optimize biphasic sample preparation. Biphasic samples of model compounds were then used to test out classic slice selection NMR experiments, and to test out the novel one-shot double-slice one-dimensional experiment and the two-dimensional TOCSY version that were developed through this work. Once the model compound biphasic sample experiments were proven successful, the experiments were expanded to more complex biphasic samples that are more representative of real-life samples. The samples used to test these experiments were in-tube extractions of tea leaves and of hot and cold brewed coffees. The result of this research is a novel experiment that provides information about two different regions (or phases, in the case of biphasic samples) simultaneously in a single experiment. This experiment was proven to be robust and easy to implement, and it presents new opportunities for the field of slice selection NMR spectroscopy.
Description
Keywords
NMR, Nuclear magnetic resonance spectroscopy, One-shot double-slice, Pulsed field gradient, Shaped pulse, Slice selective NMR