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Analysis of the behaviour of confined molecules using 2H T1 nuclear magnetic relaxation dispersion
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-9277-4534
2019 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028Article in journal (Refereed) Epub ahead of print
Abstract [en]

A four-site exchange model is developed in order to explain deuterium -nuclear magnetic relaxation dispersion (NMRD) profiles of acetonitrile in silica pore systems. The four-site exchange model comprises a bulk, surface and two types of burried or cavity sites. It is found that the residence time of acetonitrile- at a flat Si-surface is less than 100 ps. No bilayer-like ordering of acetonitrile is formed at the Si-surface because no quadrupole splitting was observed. The dispersion in the deuterium T1-NMRD profiles are due to relatively few so-called beta-sites with molecular residence time in the range 0.2-2 micro seconds. This deuterium T-NMR dispersion experiment suggest that the retention time of different analysts can be studied in terms of their residence time in beta sites.

Place, publisher, year, edition, pages
Taylor & Francis, 2019.
Keywords [en]
Spin-lattice relaxation time of acetonitrile-d3, NMRD, molecular origin of the retention time, 4-site exchange model
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-162676DOI: 10.1080/00268976.2019.1645367ISI: 000479433000001OAI: oai:DiVA.org:umu-162676DiVA, id: diva2:1347737
Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2020-01-08
In thesis
1. Study of retention mechanisms in Hydrophilic Interaction Chromatography by Nuclear Magnetic Resonance Spectroscopy
Open this publication in new window or tab >>Study of retention mechanisms in Hydrophilic Interaction Chromatography by Nuclear Magnetic Resonance Spectroscopy
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with investigations of the retention mechanisms in hydrophilic interaction liquid chromatography (HILIC) using nuclear magnetic resonance spectroscopy. The aims are to understand how the different types of stationary phases can influence the retention of various solutes and the adsorption abilities of solvent on stationary phases.

The thesis encompasses the development of a saturation transfer diffe­rence nuclear magnetic resonance (STD-NMR) spectroscopy method by which the mechanisms in HILIC were probed on hydrophilic and polar stationary phases with varying charge properties and water-retaining abilities under high-resolution magic angle spinning (HR-MAS) condit­ions. By applying the developed method, results show that toluene is in­deed capable of traversing the water-enriched layers of all the three tested stationary phases. In addition, the STD-NMR method was applied to study interaction mechanisms using set hydrophilic compounds rang­ing from small organic acids, nucleobases, nucleosides, and other neutral molecules to further elucidate the differences in HILIC selectivity caused by a dipolar interaction, hydrogen bonding, and electrostatic interaction.

Finally, the solvent adsorption on the stationary surface was studied by applying a nuclear magnetic relaxation dispersion (NMRD) technique in combination with a relaxation model in order to resolve the deuterium T1-NMRD profile of acetonitrile-d3 in aqueous solutions confined in the pores of modified HILIC silicas with nominal pore diameters ranging from of 6 to 10 nm. It was found that the acetonitrile-d3 had a strong field dependence at low magnetic fields, which was attri­buted to surface sites at which the molecules were trapped with residence times in the range of 0.1–3 µs.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2020. p. 67
Keywords
HILIC, hydrophilic interaction chromatography, adsorption, STD-NMR, saturation transfer difference, retention mechanism, NMRD, solid state-NMR
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-166938 (URN)978-91-7855-180-4 (ISBN)978-91-7855-181-1 (ISBN)
Public defence
2020-01-31, Lilla hörsalen (KB.E3.01), KBC-huset Linnaeus väg 10, Umeå, 10:00 (English)
Opponent
Supervisors
Note

Alternative author name as stated on thesis cover: Adelijiang Xiamuxiding. 

Digital ISBN incorrectly labeled as ISSN in the publication. 

Available from: 2020-01-10 Created: 2020-01-07 Last updated: 2020-01-09Bibliographically approved

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Shamshir, AdelSparrman, TobiasWestlund, Per-Olof

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