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1. Edström, Emelie. Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions.

Degree: Engineering and Chemical Sciences, 2015, Karlstad University

Chromatography is a widely used separation technique including many different modes, for example supercritical fluid chromatography (SFC) which uses a supercritical fluid as mobile phase. A supercritical fluid is achieved when a substance is subjected to a temperature and pressure above the critical point and the boundary between the liquid phase and gas phase is erased. The interest for SFC has increased in recent years, mainly for separation of chiral molecules in the pharmaceutical industry. What makes SFC interesting is that it is a quick, cost-efficient and green method. This is in part due to less organic solvent used in the mobile phase in SFC compared with liquid chromatography and that the carbon dioxide that represents the major part of the mobile phase is a by-product from other processes. In SFC modifiers, often small alcohols, are added to carbon dioxide based mobile phase in order to increase the solubility of polar compounds. In this study the adsorption of methanol to two different stationary phases; Kromasil-Diol and chiral Lux Cellulose-4 were studied. Adsorption is a phenomenon where surface interactions crate a higher density of molecules at the surface than in the bulk. The aim of this work has been to study the adsorption of modifier (methanol) to the stationary phase both to determine the extent of adsorption and the kinetics for system equilibration. These findings were then put into perspective of normal use of SFC for separation of molecules. There are a number of techniques for measuring adsorption; in this study the tracer pulse method is used. This is a pulse method where a concentration plateau is created and an isotope labelled molecule is injected. This was performed in the mobile phase composition from pure carbon dioxide to pure methanol. In addition to the tracer pulse experiments the isotope effect, the eluent flow, equilibration times for the column and retention times for a set of analytes were measured. For the Diol column no large isotope effect was observed, the method was also proved to be highly reproducible since several runs gave consistent results. Calculations based on the experimental data showed that a 6.3 Å thick layer was built up at a methanol fraction of 13% (v/v), corresponding to a monolayer. Changes of the methanol fraction below the saturation level has has greater effect on the retention factor for the analytes than at higher methanol fractions, when the monolayer was saturated. The conclusion of this is that SFC is more stable in the area where the layer has been built up. A preliminary study has been made for the chiral Lux Cellulose-4 column which was not as conclusive as for the Kromasil-Diol column. This type of column needs further studies to confirm the deviating observations and to investigate the cause for these.

Subjects/Keywords: SFC; excess adsorption isotherm; methanol; tracer pulse

…the surface specific excess adsorption isotherm, Γ, this has to be divided by the surface… …eluent. The excess adsorption isotherm, Γ, follows a characteristic shape, see Figure 3.1… …can explain the characteristic shape of the excess adsorption isotherm (Figure 3.1)… …Figure 1.3 e-f). Figure 3.1 The excess adsorption isotherm (-) consist of an… …pure CO2 as eluent. The peaks were detected at 196nm. 4.4.2 Excess adsorption isotherm The… 

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APA (6th Edition):

Edström, E. (2015). Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions. (Thesis). Karlstad University. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-35185

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Edström, Emelie. “Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions.” 2015. Thesis, Karlstad University. Accessed May 08, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-35185.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Edström, Emelie. “Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions.” 2015. Web. 08 May 2021.

Vancouver:

Edström E. Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions. [Internet] [Thesis]. Karlstad University; 2015. [cited 2021 May 08]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-35185.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Edström E. Solvent adsorption in SFC : Adsorption of methanol under supercritical conditions. [Thesis]. Karlstad University; 2015. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-35185

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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