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A closer study of methanol adsorption and its impact on solute retentions in supercritical fluid chromatography
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). (INTERACT)
AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
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2016 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1442, p. 129-139Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Surface excess adsorption isotherms of methanol on a diol silica adsorbent were measured in supercritical fluid chromatography (SFC) using a mixture of methanol and carbon dioxide as mobile phase. The tracer pulse method was used with deuterium labeled methanol as solute and the tracer peaks were detected using APCI-MS over the whole composition range from neat carbon dioxide to neat methanol. The results indicate that a monolayer (4 angstrom) of methanol is formed on the stationary phase. Moreover, the importance of using the set or the actual methanol fractions and volumetric flows in SFC was investigated by measuring the mass flow respective pressure and by calculations of the actual volume fraction of methanol. The result revealed a significant difference between the value set and the actually delivered volumetric methanol flow rate, especially at low modifier fractions. If relying only on the set methanol fraction in the calculations, the Methanol layer thickness should in this system be highly overestimated. Finally, retention times for a set of solutes were measured and related to the findings summarized above concerning methanol adsorption. A strongly non-linear relationship between the logarithms of the retention factors and the modifier fraction in the mobile phase was revealed, prior to the established monolayer. At modifier fractions above that required for establishment of the methanol monolayer, this relationship turns linear which explains why the solute retention factors are less sensitive to changes in modifier content in this region.

Place, publisher, year, edition, pages
2016. Vol. 1442, p. 129-139
Keywords [en]
Supercritical fluid chromatography, SFC, Excess adsorption, Solvent adsorption, Tracer-pulse method, Solute retention
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-42028DOI: 10.1016/j.chroma.2016.03.006ISI: 000374083100014PubMedID: 26979267OAI: oai:DiVA.org:kau-42028DiVA, id: diva2:927968
Available from: 2016-05-13 Created: 2016-05-13 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)
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Supervisors
Available from: 2020-02-20 Created: 2019-11-18 Last updated: 2020-02-20Bibliographically approved

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Glenne, EmelieSamuelsson, JorgenFornstedt, Torgny

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