| 1. |
- Bagge, Joakim, et al.
(författare)
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Impact of stationary-phase pore size on chromatographic performance using oligonucleotide separation as a model
- 2020
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1634, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- A combined experimental and theoretical study was performed to understand how the pore size of packing materials with pores 60-300 angstrom in size affects the separation of 5-50-mer oligonucleotides. For this purpose, we developed a model in which the solutes were described as thin rods to estimate the accessible surface area of the solute as a function of the pore size and solute size. First, an analytical investigation was conducted in which we found that the selectivity increased by a factor of 2.5 when separating 5- and 15-mer oligonucleotides using packing with 300 angstrom rather than 100 angstrom pores. We complemented the analytical investigation by theoretically demonstrating how the selectivity is dependent on the column's accessible surface area as a function of solute size. In the preparative investigation, we determined adsorption isotherms for oligonucleotides using the inverse method for separations of a 9- and a 10-mer. We found that preparative columns with a 60 angstrom-pore-size packing material provided a 10% increase in productivity as compared with a 300 A packing material, although the surface area of the 60 angstrom packing is as much as five time larger.
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| 2. |
- Browne, Michael, et al.
(författare)
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Parallelization of MATLAB for Euro50 integrated modeling
- 2004
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Ingår i: Modeling and Systems Engineering for Astronomy (Proceedings of the SPIE). - : SPIE. - 081945429X ; 5497, s. 604-610
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Konferensbidrag (refereegranskat)abstract
- MATLAB and its companion product Simulink are commonly used tools insystems modelling and other scientific disciplines. A cross-disciplinaryintegrated MATLAB model is used to study the overall performance of theproposed 50m optical and infrared telescope, Euro50. However thecomputational requirements of this kind of end-to-end simulation of thetelescope's behaviour, exceeds the capability of an individualcontemporary Personal Computer. By parallelizing the model, primarily ona functional basis, it can be implemented across a Beowulf cluster ofgeneric PCs. This requires MATLAB to distribute in some way data andcalculations to the cluster nodes and combine completed results. Therehave been a number of attempts to produce toolkits to allow MATLAB to beused in a parallel fashion. They have used a variety of techniques. Herewe present findings from using some of these toolkits and proposedadvances.
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| 3. |
- Enmark, Martin, 1984-, et al.
(författare)
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A closer study of peak distortions in supercritical fluid chromatography as generated by the injection
- 2015
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673 .- 1873-3778. ; 1400, s. 131-139
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Tidskriftsartikel (refereegranskat)abstract
- Abstract In SFC the sample cannot be dissolved in the mobile phase, so it is often dissolved in pure modifier, or another liquid, sometimes resulting in serious distortions of the eluted peak profiles already at moderately high injection volumes. It is suspected the reasons for these effects are solvent strength mismatch and/or viscosity mismatch. This study presents a systematic and fundamental investigation of the origin of these peak deformations due to the injection solvent effects in SFC, using both systematic experiments and numerical modeling. The first set of experiments proved that the injection volume and the elution strength of the sample solution had a major impact of the shapes of the eluted peaks. Secondly, the sample band elution profile was numerically modeled on a theoretical basis assuming both un-retained and retained co-solvent injection plugs, respectively. These calculations quantitatively confirmed our first set of experiments but also pointed out that there is also an additional significant effect. Third, viscous fingering experiments were performed using viscosity contrast conditions imitating those encountered in SFC. These experiments clearly proved that viscous fingering effects play a significant role. A new method for determination of adsorption isotherms of solvents was also developed, called the “Retention Time Peak Method” (RTPM). The RTPM was used for fast estimation of the adsorption isotherms of the modifier and required using only two experiments.
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| 4. |
- 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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| 5. |
- Enmark, Martin, et al.
(författare)
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A Deeper Understanding of a Complex Adsorption Behavior in a Common Chiral, Separation System
- 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) was investigated. This separation has previously been performed and analyzed on a methylcellulose tribenzoate coated CSP. In that case, both enantiomers could be described with a bi-Langmuir adsorption isotherm, convex upwards (type I). In our case, two fundamentally different properties were observed. First, the elution order was reversed. Furthermore, only the less retained enantiomer shows type I adsorption behavior, while the adsorption isotherm of the more retained compound contained an inflection point at low concentration. To analyze these differences, adsorption isotherms were determined and further analyzed using Scatchard plots and 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-idealadsorbate-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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| 6. |
- Enmark, Martin, 1984-, et al.
(författare)
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A Retention-Matching Strategy for Method Transfer in Supercritical Fluid Chromatography : Introducing the Isomolar Plot Approach
- 2021
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 93:16, s. 6385-6393
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Tidskriftsartikel (refereegranskat)abstract
- A strategy to match any retention shifts due to increased or decreased pressure drop during supercritical fluid chromatography (SFC) method transfer is presented. The strategy relies on adjusting the co-solvent molarity without the need to adjust the back-pressure regulator. Exact matching can be obtained with minimal changes in separation selectivity. To accomplish this, we introduce the isomolar plot approach, which shows the variation in molar co-solvent concentration depending on the mass fraction of co-solvent, pressure, and temperature, here exemplified by CO2-methanol. This plot allowed us to unify the effects of the co-solvent mass fraction and density on retention in SFC. The approach, which was verified on 12 known empirical retention models for each enantiomer of six basic pharmaceuticals, allowed us to numerically calculate the apparent retention factor for any column pressure drop. The strategy can be implemented either using a mechanistic approach if retention models are known or empirically by iteratively adjusting the co-solvent mass fraction. As a rule of thumb for the empirical approach, we found that the relative mass fraction adjustment needed is proportional to the relative change in the retention factor caused by a change in the pressure drop. Different proportionality constants were required to match retention in the case of increasing or decreasing pressure drops.
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| 7. |
- 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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| 8. |
- Enmark, Martin, et al.
(författare)
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A systematic investigation on the accuracy of computer simulations for optical isomers in industrial settings
- 2010
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Konferensbidrag (refereegranskat)abstract
- Predicting the band profiles of typical chromatographic separations using the approach of the inverse method (IM) [2] requires finding the numerical solution of the Equilibrium-Dispersive (ED) mass balance equation [1]. The accuracy of the determination of the competitive adsorption isotherms is therefore explicitly dependent on the choice of algorithm to solve the ED model. Earlier studies have shown that the well known RFD algorithm [3] has limitations in its accuracy for certain simulated conditions such as column efficiency and adsorption isotherm type [5]. In this study, we thoroughly investigate three different algorithms, the rapid and well known Rouchon Finite Difference (RFD) algorithm [3], the Orthogonal Collocation on Finite Elements (OCFE) method [4] and the Central Difference Method (CDM) algorithm developed by us. Firstly, a systematic investigation is made, comparing the different algorithms under a broad range of different synthetic conditions. Secondly, we apply all three algorithms using the IM on real experimental systems; (I) one high efficiency quaternary separation and (II) one pharmaceutical industry application with a chiral intermediate separation. We have found discrepancies between the conventional (RFD) and the more accurate (OCFE and CDM) algorithms for several synthetic 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 of OCFE/CDM for a binary low efficiency separation problem. Our conclusion is to use the RFD algorithm with caution when any of the particular conditions we have investigated is valid. When the highest accuracy is sought, there is no doubt that OCFE or CDM should be the algorithms of choice. However, given the computational speed of RFD, we also recommend it for preliminary parameter fitting. For conditions where we have shown the algorithms to produce practically identical solutions, RFD can be applied with greater certainty. It remains to be thoroughly investigated the effect on the particular shape of the adsorption isotherm on the obtained solution, for example type III having inflection points.
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| 9. |
- Enmark, Martin, et al.
(författare)
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A thermodynamic and kinetic study of an unusual adsorption behavior-Methyl Mandelate on commercially available Tris-(3,5- dimethylphenyl)carbamoyl Cellulose Chiral Stationary Phase
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The adsorption equilibria of racemic methyl mandelate on a tris-(3,5- dimethylphenyl)carbamoyl cellulose chiral stationary phase (CSP) was investigated. The following were observed, the less retained enantiomer shows “Langmuirian†(type I) adsorption behavior, while the adsorption isotherm of the more retained compound contained an inflection point at low concentration. To analyze these differences, adsorption isotherms were determined and further analyzed using Scatchard plots and adsorption energy distribution (AED) calculations. The less retained enantiomer was best described by heterogeneous unimodal adsorption model (Tóth) while the second enantiomer was best described with a heterogeneous adsorption model with adsorbate-adsorbate interactions (bi-Moreau). The adsorption behavior of both enantiomers was also studied at several different temperatures and it was found to be exothermic; in addition, the non-idealadsorbate-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. This is an industrial – academic cooperation in the Fundamental Separation Science Group www.separationscience.se
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| 10. |
- Enmark, Martin, et al.
(författare)
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Adsorption Isotherm Determination for Reliable Phase System Characterization in SFC : Challenges and Pitfalls
- 2012
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Konferensbidrag (refereegranskat)abstract
- Recently the pharmaceutical industry has started to replace HPLC with SFC because of incentives to lower the environmental impact and as well as increasing performance. Reliable characterization of the adsorption processes in SFC, is therefore of utmost importance. The key thermodynamic phase system information is obtained by rigorous determination of adsorption isotherms over a broad concentration range. If properly processed, this data gives not only correct information about the degree of heterogeneity but also the values of the energy of interactions and monolayer capacities of each individual type of adsorption site in the phase system; ultimately, this can result in identification of the types of interactions (dipole-dipole, van der Waals interactions etc.). In this study, we will present the transfer of LC adsorption characterization methods to SFC conditions using several model compounds with several different methods for adsorption isotherm determination traditionally applied with success in LC, and now modified for SFC. We have limited our investigation to methanol as modifier and used the operational conditions, temperature and backpressure most typically observed in industrial settings; in addition, we have used commercial standard SFC-equipment. The results clearly shows that adsorption isotherm determinations in SFC are considerably more complicated than in LC; we will go through the most important pitfalls and give guidelines for more rigorous determinations of adsorption data in SFC. This is an industrial – academic cooperation in the Fundamental Separation Science Group www.separationscience.se
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