| 1. |
- Enmark, Martin, et al.
(författare)
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A Deeper Investigation of Strange Preparative Band Shapes of a Simple Racemic Solute on tris-(3, 5- dimethylphenyl)carbamoyl Cellulose as Chiral Stationary Phase
- 2011
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Konferensbidrag (refereegranskat)abstract
- The adsorption equilibria of racemic methyl mandelate on a tris-(3, 5-dimethylphenyl)carbamoyl cellulose chiral stationary phase (CSP) has a peculiar behavior. The preparative band shape of the more retained enantiomer was very unusual with an inflection point at low concentrations whereas the less retained enantiomer shows normal type I adsorption behavior. For a deeper understanding of this separation adsorption isotherms were determined and further analyzed with Scatchard plots combined with adsorption energy distribution calculations. The less retained enantiomer was best described by Tóth adsorption isotherm while the second enantiomer was best described with a bi-Moreau adsorption isotherm. The Moreau model is an extension of the Langmuir model including non-ideal adsorbate-adsorbate interactions; here the unusual model provided an explanation to the non-ideal adsorption of the more retained enantiomer. Furthermore, the possibility of using the Moreau model as a local model for adsorption in AED calculations was evaluated by synthetically generated raw adsorption slope data. It was demonstrated that the AED accurately could predict the number of adsorption sites for the generated data. The adsorption behavior of both enantiomers was also studied at several different temperatures and it was found to be exothermic; in addition, the non-ideal adsorbate-adsorbate interaction strength decreases with increasing temperature. Stochastic analysis of the adsorption process could identify a single kinetic site for each enantiomer. The average amount of adsorption/desorption events increases and the sojourn time decreases with increasing temperature
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| 2. |
- Enmark, Martin, et al.
(författare)
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Characterization of an unusual adsorption behavior of racemic methyl-mandelate on a tris-(3,5-dimethylphenyl) carbamoyl cellulose chiral stationary phase
- 2011
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1218:38, s. 6688-6696
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Tidskriftsartikel (refereegranskat)abstract
- An interesting adsorption behavior of racemic methyl mandelate on a tris-(3,5-dimethylphenyl)carbamoyl cellulose chiral stationary phase was theoretically and experimentally investigated. The overloaded band of the more retained enantiomer had a peculiar shape indicating a type V adsorption isotherm whereas the overloaded band of the less retained enantiomer had a normal shape indicating a type I adsorption behavior. For a closer characterization of this separation, adsorption isotherms were determined and analyzed using an approach were Scatchard plots and adsorption energy distribution (AED) calculations are combined for a deeper analysis. It was found that the less retained enantiomer was best described by a Tóth adsorption isotherm while the second one was best described with a bi-Moreau adsorption isotherm. The latter model comprises non-ideal adsorbate–adsorbate interactions, providing an explanation to the non-ideal adsorption of the more retained enantiomer. Furthermore, the possibility of using the Moreau model as a local model for adsorption in AED calculations was evaluated using synthetically generated raw adsorption slope data. It was found that the AED accurately could predict the number of adsorption sites for the generated data. The adsorption behavior of both enantiomers was also studied at several different temperatures and found to be exothermic; i.e. the adsorbate–adsorbate interaction strength decreases with increasing temperature. Stochastic analysis of the adsorption process revealed that the average amount of adsorption/desorption events increases and the sojourn time decreases with increasing temperature.
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| 3. |
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| 4. |
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| 5. |
- Samuelsson, Jörgen, et al.
(författare)
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Expanding the elution by characteristic point method for determination of various types of adsorption isotherms
- 2011
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1218:24, s. 3737-3742
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Tidskriftsartikel (refereegranskat)abstract
- Important improvements have recently been made on the elution by characteristic point (ECP) method to increase the accuracy of the determined adsorption isotherms. However, the method has so far been limited/used for only type I adsorption isotherms (e.g. Langmuir, Toth, bi-Langmuir). In this study, general strategies are developed to expand the ECP method for the determination of more complex adsorption isotherms including such containing inflection points. We will exemplify the methodology with type II, type III and type V isotherms. Guidelines are given for how to determine such isotherms using the ECP method and for the experimental considerations that must be taken into account or that may be eliminated in the particular case.
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| 6. |
- Samuelsson, Jörgen, et al.
(författare)
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Improvement in the generation of adsorption isotherm data in the elution by characteristic points method- : the ECP-slope approach
- 2010
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1217:46, s. 7215-7221
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Tidskriftsartikel (refereegranskat)abstract
- The elution by characteristic points (ECP) method is a very rapid and precise method for determination of the phase system equilibrium of phase systems in broad solute concentration ranges. Thus, the method is especially suitable for rapid characterization of high efficient separation systems. One important source of error, the effects by the post-loop dispersion, was eliminated in a recent investigation. In this study, the systematic error caused by the selection of the integration starting point at concentration equal to 0 is eliminated. This is done by developing and validating a new procedure for isotherm data generation; the ECP-slope method. The method generates raw slope data of the adsorption isotherm instead of raw adsorption data by integrations as the classical ECP does. Both numerical and experimental data were used for the comparison of the classical ECP approach with the slope-ECP method
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| 7. |
- Undin, Torgny, 1975-
(författare)
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Development and improvement of methods for characterization of HPLC stationary phases
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High Performance Liquid Chromatography (HPLC) is a widely used tech-nique both for detecting and purifying substances in academy and in the industry. In order to facilitate the use of, and knowledge in HPLC, character-ization of stationary phases is of utmost importance. Tailor made characteri-zation methods and workflows are steadily increasing the speed and accura-cy in which new separation systems and methods are developed. In the field fundamental separation science and of preparative chromatography there is always the need for faster and more accurate methods of adsorption isotherm determination. Some of that demand are met with the steadily increase of computational power, but the practical aspects on models and methods must also be further developed. These nonlinear characterization methods will not only give models capable of describing the adsorption isotherm but also actual values of local adsorption energies and monolayer saturation capacity of an individual interaction sites etc.The studies presented in this thesis use modern alkali stable stationary phas-es as a model phase, which will give an insight in hybrid materials and their separation mechanism. This thesis will include an update and expansion in using the Elution by Characteristic Points (ECP) method for determination of adsorption isotherms. The precision is even further increased due to the ability to use slope data as well as an increase in usability by assigning a set of guidance rules to be applied when determine adsorption isotherms having inflection points. This thesis will further provide the reader with information about stationary phase characterization and the power of using existing tech-niques; combine them with each other, and also what the expansion of meth-ods can revile in terms of precision and increased usability. A more holistic view of what benefits that comes with combining a non-linear characteriza-tion of a stationary phase with more common linear characterization meth-ods are presented.
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| 8. |
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| 9. |
- Undin, Torgny, et al.
(författare)
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Evaluation of a combined linear–nonlinear approach for column characterization using modern alkaline-stable columns as model
- 2013
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Ingår i: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 36:11, s. 1753-1761
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates if deeper understanding is achieved when combining nonlinear and linear chromatographic column characterization methods. As test systems, two hybrid columns (Phenomenex Gemini-NX C18 and Kromasil Eternity C18) and one classic one (Kromasil-C18) were selected. The nonlinear methods were based on firm adsorption theory and involved determination of adsorption isotherms followed by calculations with a new numerical tool, adsorption energy distribution, on probe components at different pH values. The linear methods involved the hydrophobic subtraction model and selected probe components retention factors as a function of pH. The combined analysis indicated that both complementary and confirmative information can be achieved regarding the actual model systems.
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| 10. |
- Agmo Hernández, Víctor, et al.
(författare)
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Enhanced interpretation of adsorption data generated by liquid chromatography and by modern biosensors
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1317, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- In this study we demonstrate the importance of proper data processing in adsorption isotherm estimations. This was done by investigating and reprocessing data from five cases on two closely related platforms: liquid chromatography (LC) and biosensors. The previously acquired adsorption data were reevaluated and reprocessed using a three-step numerical procedure: (i) preprocessing of adsorption data, (ii) adsorption data analysis and (iii) final rival model fit. For each case, we will discuss what we really measure and what additional information can be obtained by numerical processing of the data. These cases clearly demonstrate that numerical processing of LC and biosensor data can be used to gain deeper understanding of molecular interactions with adsorption media. This is important because adsorption data, especially from biosensors, is often processed using old and simplified methods. (C) 2013 Elsevier B.V. All rights reserved.
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