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| 2. |
- 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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| 3. |
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| 4. |
- Arnell, Robert, et al.
(författare)
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Adsorption behaviour of a quinidine carbamate-based chiral stationary phase : Role of the additive
- 2009
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1216:16, s. 3480-3487
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we incorporate the additive properties into the theoretical model of a general preparative chromatographic system; this is normally not done and this limits a proper process optimization. As a model phase system, we used the adsorption of 9H-fluoren-9-ylmethoxycarbonyl-allylglycine (Fmoc-allylglycine) enantiomers on a quinidine carbamate-based chiral stationary phase (anion exchanger) together with a methanol-glacial acetic acid-ammonium acetate eluent. The inverse method was used to measure the competitive adsorption isotherms of both the Fmoc-allylglycine enantiomers as well as the non-detectable additive acetic acid. It was concluded that this enantioselective preparative system is well described by a non-heterogeneous adsorption model and that the loading capacity is very high. The proposed model is valid over a wide range of additive concentrations, which is important for process optimization.
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| 5. |
- Enmark, Martin, et al.
(författare)
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A systematic investigation of algorithm impact in preparative chromatography with experimental verifications
- 2011
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1218:5, s. 662-672
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Tidskriftsartikel (refereegranskat)abstract
- Computer-assisted optimization of chromatographic separations requires finding the numerical solution of the Equilibrium-Dispersive (ED) mass balance equation. Furthermore, the competitive adsorption isotherms needed for optimization are often estimated numerically using the inverse method that also solves the ED equations. This means that the accuracy of the estimated adsorption isotherm parameters explicitly depends on the numerical accuracy of the algorithm that is used to solve the ED equations. The fast and commonly used algorithm for this purpose, the Rouchon Finite Difference (RFD) algorithm, has often been reported not to be able to accurately solve the ED equations for all practical preparative experimental conditions, but its limitations has never been completely and systematically investigated. In this study, we thoroughly investigate three different algorithms used to solve the ED equations: the RFD algorithm, the Orthogonal Collocation on Finite Elements (OCFE) method and a Central Difference Method (CDM) algorithm, both for increased theoretical understanding and for real cases of industrial interest. We identified discrepancies between the conventional RFD algorithm and the more accurate OCFE and CDM algorithms for several conditions, such as low efficiency, increasing number of simulated components and components present at different concentrations. Given high enough efficiency, we experimentally demonstrate good prediction of experimental data of a quaternary separation problem using either algorithm, but better prediction using OCFE/CDM for a binary low efficiency separation problem or separations when the compounds have different efficiency. Our conclusion is to use the RFD algorithm with caution when such conditions are present and that the rule of thumb that the number of theoretical plates should be greater than 1000 for application of the RFD algorithm is underestimated in many cases
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| 6. |
- Enmark, Martin, 1984-, et al.
(författare)
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Determination of adsorption isotherms in supercritical fluid chromatography
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1312, s. 124-133
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Tidskriftsartikel (refereegranskat)abstract
- Abstract In this study we will demonstrate the potential of modern integrated commercial analytical SFC-systems for rapid and reliable acquisition of thermodynamic data. This will be done by transferring the following adsorption isotherm determination methods from liquid chromatography (LC) to supercritical fluid chromatography (SFC): Elution by Characteristic Points (ECP), the Retention Time Method (RTM), the Inverse Method (IM) and the Perturbation Peak (PP) method. In order to transfer these methods to SFC in a reliable, reproducible way we will demonstrate that careful system verification using external sensors of mass flow, temperature and pressure are needed first. The adsorption isotherm data generated by the different methods were analyzed and compared and the adsorption isotherms ability to predict new experimental elution profiles was verified by comparing experiments with simulations. It was found that adsorption isotherm data determined based on elution profiles, i.e., ECP, IM and RTM, were able to accurately predict overloaded experimental elution profiles while the more tedious and time-consuming PP method, based on small injections on concentration plateaus, failed in doing so.
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| 7. |
- Enmark, Martin, et al.
(författare)
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Enantioseparation of omeprazole effect of different packing particle size on productivity
- 2012
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673. ; 1240:1, s. 123-131
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Tidskriftsartikel (refereegranskat)abstract
- Enantiomeric separation of omeprazole has been extensively studied regarding both product analysis and preparation using several different chiral stationary phases. In this study, the preparative chiral separation of omeprazole is optimized for productivity using three different columns packed with amylose tris (3,5-dimethyl phenyl carbamate) coated macroporous silica (5, 10 and 25 Όm) with a maximum allowed pressure drop ranging from 50 to 400 bar. This pressure range both covers low pressure process systems (50–100 bar) and investigates the potential for allowing higher pressure limits in preparative applications in a future. The process optimization clearly show that the larger 25 Όm packing material show higher productivity at low pressure drops whereas with increasing pressure drops the smaller packing materials have substantially higher productivity. Interestingly, at all pressure drops, the smaller packing material result in lower solvent consumption (L solvent/kg product); the higher the accepted pressure drop, the larger the gain in reduced solvent consumption. The experimental adsorption isotherms were not identical for the different packing material sizes; therefore all calculations were recalculated and reevaluated assuming identical adsorption isotherms (with the 10 Όm isotherm as reference) which confirmed the trends regarding productivity and solvent consumption.
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| 8. |
- Enmark, Martin, 1984-, et al.
(författare)
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Investigation of plateau methods for adsorption isotherm determination in supercritical fluid chromatography
- 2014
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1354, s. 129-138
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Tidskriftsartikel (refereegranskat)abstract
- The Perturbation Peak (PP) method and Frontal analysis (FA) are considered as the most accurate methods for adsorption isotherms determination in liquid chromatography. In this study we investigate and explain why this is not the case in Supercritical Fluid Chromatography (SFC), where the PP method does not work at all, using a modern analytical system. The main reason was found to be that the solute to be studied must be dissolved in the MeOH reservoir before it is mixed with CO2. Since the solute occupies a certain partial volume in the reservoir, the larger the solute content the larger this fractional volume will be, and the final MeOH fraction in the mobile phase will then be smaller compared to the bulk mobile phase without solute in the modifier. If the retention of small injections on the concentration plateaus, i.e., “analytical-size” perturbation peaks, is sensitive to small variations of MeOH in the eluent, this will seriously decrease the accuracy of the PP method. This effect was verified and compensated for and we also demonstrated that the same problem will occur in frontal analysis, another concentration plateau method.
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| 9. |
- Fornstedt, Torgny, 1957-, et al.
(författare)
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Injection profiles in liquid chromatography. I. A fundamental investigation
- 2010
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1217:26, s. 4306-4312
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Tidskriftsartikel (refereegranskat)abstract
- This is a fundamental experimental and theoretical investigation on how the injection profile depends on important experimental parameters. The experiments revealed that the injection profile becomes more eroded with increased (i) flow rate, (ii) viscosity of the eluent, (iii) size of the solute, (iv) injection volume and (v) inner diameter of the injection loop capillary. These observations cannot be explained by a 1D-convection-diffusion equation, since it does not account for the effect of the parabolic flow and the radial diffusion on the elution profile. Therefore, the 1D model was expanded into a 2D-convection-diffusion equation with cylindrical coordinates, a model that showed a good agreement with the experimental injection profiles dependence on the experimental parameters. For a deeper understanding of the appearance of the injection profile the 2D model is excellent, but to account for injection profiles of various injection volumes and flow rates in preparative and process-chromatography using computer-optimizations, a more pragmatic approach must be developed. The result will give guidelines about how to reduce the extra-column variance caused by the injection profile. This is important both for preparative and analytical chromatography; in particular for modern analytical systems using short and narrow columns
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| 10. |
- Forssen, Patrik, et al.
(författare)
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A model free method for estimation of complicated adsorption isotherms in liquid chromatography
- 2015
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1409, s. 108-115
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Tidskriftsartikel (refereegranskat)abstract
- Here we show that even extremely small variations in the adsorption isotherm can have a tremendous effect on the shape of the overloaded elution profiles and that the earlier in the adsorption isotherms the variation take place, the larger its impact on the shape of the elution profile. These variations are so small that they can be "hidden" by the discretization and in the general experimental noise when using traditional experimental methods, such as frontal analysis, to measure adsorption isotherms. But as the effects of these variations are more clearly visible in the elution profiles, the Inverse Method (IM) of adsorption isotherm estimation is an option. However, IM usually requires that one selects an adsorption isotherm model prior to the estimation process. Here we show that even complicated models might not be able to estimate the adsorption isotherms with multiple inflection points that small variations might give rise to. We therefore developed a modified IM that, instead of fixed adsorption isotherm models, uses monotone piecewise interpolation. We first validated the method with synthetic data and showed that it can be used to estimate an adsorption isotherm, which accurately predicts an extremely "strange" elution profile. For this case it was impossible to estimate the adsorption isotherm using IM with a fixed adsorption model. Finally, we will give an example of a real chromatographic system where adsorption isotherm with inflection points is estimated by the modified IM.
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