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Peak deformations in preparative supercritical fluid chromatography due to co-solvent adsorption
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
AstraZeneca R&D, Innovat Med, 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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2016 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1468, p. 200-208Article in journal (Refereed) Published
Abstract [en]

In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as main solvent and smaller amounts of an organic polar solvent (often an alcohol) as co-solvent. The co-solvent is considered to function by changing the overall polarity of the eluent, i.e. by acting as a "modifier". However, recent studies indicate that the co-solvent methanol can also adsorb to some common SFC stationary phases. Hence, the co-solvent should also be able to function as an "adsorbing additive", i.e. an eluent component that competes with the injected solutes about the stationary phase surface. In this study it was found by fitting different mechanistic models to systematic experimental data, that the co-solvent methanol can have both functions: at low co-solvent fractions, methanol acts as an additive whereas at larger fractions it acts as a modifier. Moreover, it was found that when the co-solvent adsorbs more strongly to the stationary phase than the solute, "bizarre" deformations of the preparative band shapes can occur. This is illustrated by a solute that converts from a normal "Langmuirian" band shape to an "anti-Langmuirian" shape when changing from neat carbon dioxide (CO2) to an eluent containing co-solvent. This peak shape transition is dependent on both (i) the relative retention of the solute and co-solvent to the stationary phase in eluent containing neat CO2 and on (ii) the relative retention of the additive perturbation peak and the solute peak in eluent containing also co-solvent. 

Place, publisher, year, edition, pages
2016. Vol. 1468, p. 200-208
Keywords [en]
Supercritical fluid chromatography, SFC, Solvent adsorption, Adsorption strength, Langmuir band shape, Anti-Langmuir band shape
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kau:diva-47585DOI: 10.1016/j.chroma.2016.09.019ISI: 000385326500025PubMedID: 27641721OAI: oai:DiVA.org:kau-47585DiVA, id: diva2:1062288
Available from: 2017-01-05 Created: 2017-01-05 Last updated: 2019-11-18Bibliographically 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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