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Investigations of the retention mechanisms in hydrophilic interaction chromatography
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Knut Irgum)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrophilic interaction chromatography is well known as a powerful technique separation of polar and ionizable compound nowadays. However the retention mechanism of the technique is still under debate. Understanding retention mechanism would facilitate the method development using the technique and its future improvement. This was inspiring and became the goal of this thesis.

This work involves the characterization of the water enriched layer regarding to water and buffer salt accumulation. Twelve HILIC stationary phase with a diverse surface chemistry regarding to function groups and modification type were studied. Effect of water and salt on regarding to the retention mechanism was investigated by correlating the adsorption data to the retention of selected solutes

This also involved the characterization of interactions involve in the separation of 21 HILIC columns. Interactions was probe by retention ratio of pair solutes which are characteristic for each specific interaction. The data was evaluate using principle component analysis – a multivariable data analysis method. The model was comprehensive and its outcomes were confirmed by the studies on adsorptions of water and salts.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2013. , 42 p.
Keyword [en]
HILIC, hydrophilic interaction chromatography, adsorption isotherm, water enriched layer, multivariate data analysis, retention mechanism, separation
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-68071ISBN: 978-91-7459-630-4 (print)OAI: oai:DiVA.org:umu-68071DiVA: diva2:615745
Public defence
2013-05-03, KBC Building, Room KB3A3, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2013-04-12 Created: 2013-04-11 Last updated: 2013-05-14Bibliographically approved
List of papers
1. Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention
Open this publication in new window or tab >>Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention
2013 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1320, 33-47 p.Article in journal (Other academic) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
HILIC, HPLC, Retention mechanism, Stationary phases, Eluents
National Category
Analytical Chemistry Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-68067 (URN)10.1016/j.chroma.2013.09.061 (DOI)000327922100005 ()
Funder
Swedish Research Council, 2008-3621, 2012-4000
Note

Manuscript version included in dissertation with the title: Water uptake on polar stationary phases under HILIC conditions and its relation to solute retention

Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved
2. Accumlations of ammonium acetate on polar materials under HILIC condition and its relation to retention of analytes
Open this publication in new window or tab >>Accumlations of ammonium acetate on polar materials under HILIC condition and its relation to retention of analytes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Ammonium acetate is a buffer salt commonly added to mobile phase in HILIC to improve the reproducibility of the retention of analytes. Adding buffer salt would then result to the change in retention and selectivity. In this study, we have developed methods for determine ammonium acetate in form of its hydrolyzed products (ammonium ion and acetate ion) adsorption on twelve different HILIC stationary phases under various mobile phase condition. The effect of functional group and mobile phase compositions on salt adsorption was then discussed. We also tried to develop a method for characterization important retention mechanism of HILIC systems and interpreted them under the relationship with salt adsorption. Adsorption of salt was based on both portioning and electrostatic interaction. Ammonium was found to preferentially adsorb on HILIC stationary phases except Purospher Star NH2 phase. It is worth noting that adding salt to mobile phase can promote partitioning retention mechanism, possibly as a result of phase separation due to salt out effect.

Keyword
HILIC, salt adsorption, retention mechanism
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-68070 (URN)
Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2013-04-12Bibliographically approved
3. Probing the interaction mode in hydrophilic interaction chromatography
Open this publication in new window or tab >>Probing the interaction mode in hydrophilic interaction chromatography
2011 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 35, 5880-5891 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
hydrophilic-interaction chromatography, retention factors, selectivity, column classification, partial least squares
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-46063 (URN)10.1016/j.chroma.2011.06.037 (DOI)21803363 (PubMedID)
Available from: 2011-08-25 Created: 2011-08-25 Last updated: 2017-12-08Bibliographically approved

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