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Systematic investigations of peak deformations due to co-solvent adsorption in preparative supercritical fluid chromatography
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
AstraZeneca R&D, Innovat Med & Early Dev, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
AstraZeneca R&D, Innovat Med & Early Dev, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).ORCID iD: 0000-0003-1819-1709
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2017 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1496, p. 141-149Article in journal (Refereed) Published
Abstract [en]

Strangely shaped overloaded bands were recently reported using a standard supercritical fluid chromatographic system comprising a diol column as the stationary phase and carbon dioxide with methanol as the mobile phase, Some of these overloaded elution profiles appeared strongly deformed and even had "anti-Langmuirian" shapes although their solute compounds had "Langmuirian" adsorption. To obtain a more complete understanding of the generality of these effects, the investigation was expanded to cover also other common co-solvents, such as ethanol, 2-propanol, and acetonitrile, as well as various stationary phase materials, such as silica, and 2-ethylpyridine. From this expanded study it could be confirmed that the effects of deformed overloaded solute band shapes, due to co-solvent adsorption, is general phenomena in supercritical fluid chromatographic. It could also be concluded that these effects as well as previously observed "solvent effects" or "plug effects" are entirely due to competition between the solute and solvent molecules for the adsorption sites on the stationary phase surface. Finally, guidelines were given for how to evaluate the risk of deformations occurring for a given solvent-column combination, based simply on testing retention times of solutes and co-solvent. (C) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 1496, p. 141-149
Keywords [en]
Supercritical fluid chromatography, Co-solvent adsorption, Adsorption strength, Langmuir band shape, Anti-Langmuir band shape
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kau:diva-65479DOI: 10.1016/j.chroma.2017.03.053ISI: 000400222200016PubMedID: 28366564OAI: oai:DiVA.org:kau-65479DiVA, id: diva2:1169749
Conference
16th International Symposium on Preparative and Industrial Chromatography and Allied Techniques, OCT 09-12, 2016, Vienna, AUSTRIA
Available from: 2017-12-29 Created: 2017-12-29 Last updated: 2019-12-09Bibliographically approved
In thesis
1. Fundamental Investigations of Adsorption in SFC
Open this publication in new window or tab >>Fundamental Investigations of Adsorption in SFC
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In supercritical fluid chromatography (SFC), the eluent is composed by carbon dioxide, often with additional components, in a condition between gas and liquid. This thesis aims to reach a deeper understanding of SFC by revealing the function of the additional eluent components through systematic adsorption studies.

In Paper I, investigation of surface excess adsorption isotherms of methanol revealed that a monolayer of methanol was formed. In Paper II, severe peak deformation effects due to this adsorption were shown. The findings in these papers revealed that a competitive additive model best predicts the solute retention at low methanol fractions whereas at higher fractions, methanol acts just as a modifier. In Paper III, the generality of the effects was proven by investigation of several co-solvent and stationary phase combinations. In Paper IV it was investigated how the robustness of SFC separations depend on the co-solvent adsorption, pressure, and temperature. In Paper V, the impact of the addition of amine additives was investigated. Two different mechanisms for solute peak deformations were observed.

The knowledge achieved about SFC in this theses provides guidelines for development of more robust SFC methods where peak deformations/distortions can be avoided.

Abstract [en]

In supercritical fluid chromatography (SFC) the mobile phase is composed by carbon dioxide as the main weak solvent, in a condition between a gas and a liquid. The interest in SFC has recently increased due to several advantages compared to traditional liquid chromatography (LC) such as faster sample throughput and lower environmental impact. However, there is still a lack of fundamental knowledge about SFC, among others, due to the compressible mobile phase. This thesis work aims at a deeper understanding of the functions of the mobile phase components used in SFC through systematic adsorption studies. 

In Paper I, surface excess adsorption isotherms of the co-solvent methanol on a diol silica adsorbent was investigated. It was revealed that a monolayer of methanol was formed. In Paper II, severe peak deformation effects due to this adsorption were revealed, and it was demonstrated under which conditions these deformations appear and how the co-solvent fraction can tune the shape of the eluted peak. The findings in these papers revealed that a competitive additive model best predicts the solute retention at low methanol fractions whereas at higher fractions, when a solvent layer has formed, methanol acts just as a modifier. In Paper III, the generality of the effects was proven by investigations of other co-solvent/stationary phase combinations. In Paper IV it was investigated how the robustness of SFC separations depend on the co-solvent adsorption, pressure, and temperature. In Paper V, the impact of the addition of amine additives on separation performance was investigated. Two different underlying mechanisms for solute peak distortions were revealed: (i) deformations generated by the perturbation peak and (ii) deformation due to multilayer formation promoted by the additive.

The deeper knowledge about SFC obtained in this thesis provides guidelines for development of more robust SFC methods for analysis and preparative separations where peak distortions can be avoided.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2019. p. 68
Series
Karlstad University Studies, ISSN 1403-8099 ; 2020:3
Keywords
Supercritical fluid chromatography, SFC, Adsorption isotherm, Excess adsorption isotherm, Solvent adsorption, Peak distortion, Solute retention, Overloaded peaks
National Category
Analytical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-75766 (URN)978-91-7867-070-3 (ISBN)978-91-7867-080-2 (ISBN)
Public defence
2020-03-20, Nyquistsalen, 9C 203, Karlstads universitet, Karlstad, 10:00 (English)
Opponent
Supervisors
Available from: 2020-02-20 Created: 2019-11-18 Last updated: 2020-02-20Bibliographically approved

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Glenne, EmelieSamuelsson, JörgenFornstedt, Torgny

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