| 1. |
- Dinh, Ngoc Phuoc, et al.
(författare)
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Probing the interaction mode in hydrophilic interaction chromatography
- 2011
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1218:35, s. 5880-5891
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Tidskriftsartikel (refereegranskat)abstract
- This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole, π-π interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.
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| 2. |
- Dinh, Ngoc Phuoc, 1985-, et al.
(författare)
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Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1320, s. 33-47
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In hydrophilic interaction chromatography, water is known to accumulate on the stationary phase to form a water enriched layer, which is believed to play an important role in the retention mechanism. To gain a better understanding retention mechanism in HILIC, we have determined the water uptake on twelve different HILIC stationary phases. Non-modified and monomerically functionalized silica phases followed a pattern of monolayer formation followed by multiple layer adsorption, while the water uptake on polymerically functionalized silica stationary phase showed the characteristics of formation and swelling of hydrogels. This difference in the nature of water accumulation was found to be related to different water uptake patterns when methanol and tetrahydrofuran were added to 80:20 % (v/v) acetonitrile/water by replacing 5 % of the acetonitrile as tertiary solvents, and also when ammonium acetate was added as buffering electrolyte. The relationship between water uptake and retention mechanism was investigated by looking at the correlation between retention factors of neutral analytes and phase ratios of HILIC columns, calculated either as surface area (adsorption) or volume of the water layer enriched from the acetonitrile/water eluent (partitioning). Regardless of the adsorption or partitioning mechanism, the interaction of neutral analytes and stationary phase could be mainly the hydrogen bonding between analytes and the accumulated water in the water enriched layer.
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| 3. |
- Shamshir, Adel, et al.
(författare)
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Interaction of toluene with polar stationary phases under conditions typical of hydrophilic interaction chromatography probed by saturation transfer difference nuclear magnetic resonance spectroscopy
- 2019
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Ingår i: Journal of Chromatography A. - : ELSEVIER SCIENCE BV. - 0021-9673 .- 1873-3778. ; 1588, s. 58-67
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Tidskriftsartikel (refereegranskat)abstract
- Toluene has been used as void volume (zero retention) marker since the inception of hydrophilic interaction chromatography (HILIC), based on the assumption that its hydrophobicity should prevent it from interacting with stationary phases envisioned to be covered by relatively thick layers of water. Recent work has shown that the void volumes of partly water-swollen HILIC phases are not identical to the volumes probed by toluene, yet the compound is still ubiquitously used as void volume marker. As part of our investigations of the retention mechanisms in HILIC, we probed the extent to which toluene is capable of penetrating into the water-enriched layer and to interact with the functional groups of three commercially available hydrophilic and polar stationary phases with different charge properties and water-retaining abilities, using saturation transfer difference H-1 nuclear magnetic resonance (STD-NMR) spectroscopy at high resolution magic angle spinning (HR-MAS) conditions. The test solutions were 1000 ppm of toluene in deuterated acetonitrile and water mixtures, with and without addition of ammonium acetate, in order to mimic a set of conditions typically encountered in HILIC separations. Interactions between toluene and the functional groups on the stationary phases were probed by equilibrating the phases with these eluent mimics and measuring the transfer of magnetization from stationary phase protons to the protons of toluene. Our results show that toluene is indeed capable of traversing the water-enriched layers of all the three tested phases and of interacting with protons that are tightly associated with the stationary phases. (C) 2018 Published by Elsevier B.V.
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| 4. |
- Shamshir, Adel, 1986-, et al.
(författare)
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Probing the retention mechanism of small hydrophilic molecules in hydrophilic interaction chromatography using saturation transfer difference nuclear magnetic resonance spectroscopy
- 2020
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1623
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Tidskriftsartikel (refereegranskat)abstract
- The interactions and dynamic behavior of a select set of polar probe solutes have been investigated on three hydrophilic and polar commercial stationary phases using saturation transfer difference 1 H nuclear magnetic resonance (STD-NMR) spectroscopy under magic angle spinning conditions. The stationary phases were equilibrated with a select set of polar solutes expected to show different interaction patterns in mixtures of deuterated acetonitrile and deuterium oxide, with ammonium acetate added to a total concentration that mimics typical eluent conditions for hydrophilic interaction chromatography (HILIC). The methylene groups of the stationary phases were selectively irradiated to saturate the ligand protons, at frequencies that minimized the overlaps with reporting protons in the test probes. During and after this radiation, the saturation rapidly spreads to all protons in the stationary phase by spin diffusion, and from those to probe protons in contact with the stationary phase. Probe protons that have been in close contact with the stationary phase and subsequently been released to the solution phase will have been more saturated due to a more efficient transfer of spin polarization by the nuclear Overhauser effect. They will therefore show a higher signal after processing of the data. Saturation transfers to protons in neutral and charged solutes could in some instances show clear orientation patterns of these solutes towards the stationary phases. The saturation profile of formamide and its N-methylated counterparts showed patterns that could be interpreted as oriented hydrogen bond interaction. From these studies, it is evident that the functional groups on the phase surface have a strong contribution to the selectivity in HILIC, and that the retention mechanism has a significant contribution from oriented interactions.
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| 5. |
- Wikberg, Erika, et al.
(författare)
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A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography
- 2011
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1218:38, s. 6630-6638
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Tidskriftsartikel (refereegranskat)abstract
- (2)H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4°C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the (2)H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs-Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring.
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