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  • 201.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Schmidt, H.-J.
    Schoolbooks´ and teachers´ awareness of chemists´ acid-base theories2003Conference paper (Other (popular science, discussion, etc.))
  • 202.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Schmidt, H.-J.
    Schoolbooks' and teachers' awareness of different acid-base models used in chemistry teaching2004Conference paper (Refereed)
  • 203.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Schmidt, H.-J.
    Två skandinaviska forskares syn på syror och baser. Vem tror eleverna på?2004Conference paper (Other (popular science, discussion, etc.))
  • 204.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Schmidt, H.-J.
    Upper Secondary School Students' Understanding of Models Used in Chemistry to Define Acids and Bases2005In: Science Education International. 16 (1), (2005) 39-54Article in journal (Refereed)
  • 205.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, J. H.
    Experienced Swedish science teachers' Pedagogical Content Knowledge of teaching acids-base chemistry2007Conference paper (Refereed)
  • 206.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, J. H.
    Experienced Teachers' pedagogical content knowledge of teaching acid-base chemistry2006Conference paper (Refereed)
  • 207.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, J. H.
    Experienced Teachers' pedagogical content knowledge of teaching acid-base chemistry2006Conference paper (Other academic)
  • 208.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, J. H.
    Teaching acids and bases in Swedish upper secondary schools2008Conference paper (Refereed)
  • 209.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, Jan
    ICLON, Leiden University, Graduate School of Teaching, The Netherlands.
    Experienced teachers' pedagogical content knowledge of teaching acid-base chemistry2008In: Research in science education, ISSN 0157-244X, E-ISSN 1573-1898, Vol. 38, no 5, p. 611-631Article in journal (Refereed)
    Abstract [en]

    We investigated the pedagogical content knowledge (PCK) of nine experienced chemistry teachers. The teachers took part in a teacher training course on students’ difficulties and the use of models in teaching acid–base chemistry, electrochemistry, and redox reactions. Two years after the course, the teachers were interviewed about their PCK of (1) students’ difficulties in understanding acid–base chemistry and (2) models of acids and bases in their teaching practice. In the interviews, the teachers were asked to comment on authentic student responses collected in a previous study that included student interviews about their understanding of acids and bases. Further, the teachers drew story-lines representing their level of satisfaction with their acid–base teaching. The results show that, although all teachers recognised some of the students’ difficulties as confusion between models, only a few chose to emphasise the different models of acids and bases. Most of the teachers thought it was sufficient to distinguish clearly between the phenomenological level and the particle level. The ways the teachers reflected on their teaching, in order to improve it, also differed. Some teachers reflected more on students’ difficulties; others were more concerned about their own performance. Implications for chemistry (teacher) education are discussed.

  • 210.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Van Driel, Jan
    ICLON, Leiden University, Graduate School of Teaching, The Netherlands.
    Teachers’ knowledge and beliefs about the teaching of acids and bases in Swedish upper secondary schoolsManuscript (preprint) (Other academic)
  • 211.
    Drechsler, Michal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    van Driel, Jan
    Teachers perceptions of the teaching of acids and bases in Swedish upper secondary schools2009In: Chemistry education, ISSN 1109-4028, E-ISSN 1109-4028, Vol. 10, no 2, p. 86-96Article in journal (Refereed)
  • 212. Dugo, P.
    et al.
    Presti, M.Lo.
    Öhman, Marcus
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fazio, A.
    Dugo, G.
    Mondello, L.
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Determination of flavonoids in citrus juices by micro-HPLC-ESI-MS2005In: J. Sep. Sci., 28 (2005) 1149-1156Article in journal (Refereed)
  • 213.
    Dzwilewski, Andrzej
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Anselmo, Ana Sofia
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Light induced effects in PCBM:P3HT blend films2012In: Hybrid and Organics Photovoltaics Conference: Uppsala, Sweden, 2012 / [ed] Anders Hagfeldt, SEFIN, Castelló (Spain), 2012, p. 155-155Conference paper (Refereed)
  • 214.
    Edström, Emelie
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Solvent adsorption in SFC: Adsorption of methanol under supercritical conditions2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    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.

  • 215. El-Beqqali, Aziza
    et al.
    Kussak, Anders
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Abdel-Rehim, Mohamed
    Microextraction in packed syringe / liquid chromatography /electrospray tandem mass spectrometry for quantification of acebutolol and metoprolol in human plasma and urine samples2007In: J. Liq. Chromatogr. & Relat. Technol., 30 (2007) 575-586Article in journal (Refereed)
  • 216.
    Elhamili, Anisa
    et al.
    Uppsala University, Sweden.
    Samuelsson, Jörgen
    Uppsala universitet.
    Bergquist, Jonas
    Uppsala University, Sweden.
    Wetterhall, Magnus
    Uppsala University, Sweden.
    Optimizing the extraction, separation and quantification of tricyclic antidepressant drugs in human plasma with CE-ESI-TOF-MS using cationic-coated capillaries2011In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 32, no 6-7, p. 647-658Article in journal (Refereed)
    Abstract [en]

    In this study, the extraction and CE-ESI-TOF-MS analysis of tricyclic antidepressant (TCA) drugs imipramine, desipramine, clomipramine and norclomipramine in human plasma has been optimized. The CE capillaries were modified with omega-iodo-alkyl ammonium salt (M7C4I coating) to reduce analyte adsorption to the silica wall. The use of a strong cation exchange (SCX) solid-phase extraction (SPE) column specifically designed for the extraction of basic drug species from biofluids gave very clean extracts with high and reproducible recoveries. The extraction recoveries were ranging between 87 and 91% with % RSD values of 0.5-1.7% (n = 3). The obtained strong cation exchange-SPE extracts of the TCA in human plasma only contained the analytes of interest. The optimized CE separation conditions were obtained by adding ACN and acetic acid to the sample while using an aqueous BGE. The CE-ESI-TOF-MS analysis was performed within 6 min for all TCA analytes under the optimized condition with peak efficiencies up to 1.4 x 10(5) plates/m and an average % RSD of the migration times of the analytes of 0.3% (n = 5). The presented method can readily be used for the extraction and quantification of basic drug species in human biological fluids and in pharmaceutical formulations.

  • 217.
    Enmark, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fundamental Investigations of Supercritical Fluid Chromatography2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis aims at a deeper understanding of Supercritical Fluid

    Chromatography (SFC). Although preparative SFC has started to replace Liquid Chromatography (LC) in the pharmaceutical industry - because of its advantages in speed and its less environmental impact - fundamental understanding is still lacking. Therefore there is no rigid framework to characterize adsorption or to understand the impact of changes in operational conditions.

     

    In Paper I we demonstrated, after careful system verification, that most methods applied to determine adsorption isotherms in LC could not be applied directly in SFC. This was mainly due to operational differences and to the fact that the fluid is compressible which means that everything considered constant in LC varies in SFC.

     

    In Paper II we showed that the most accurate methods for adsorption isotherm determination in LC, the so called plateau methods, do not work properly for SFC. Instead, methods based on overloaded profiles should be preferred.

     

    In Paper III a Design of Experiments approach was successfully used to quantitatively describe the retention behavior of several solutes and the productivity of a two component separation system. This approach can be used to optimize SFC separations or to provide information about the separation system.

     

    In Paper IV severe peak distortion effects, suspected to arise from injection solvent and mobile phase fluid mismatches, were carefully investigated using experiments and simulations. By this approach it was possible to examine the underlying reasons for the distortions, which is vital for method development.

     

    Finally, in Paper V, the acquired knowledge from Paper I-IV was used to perform reliable scale-up in an industrial setting for the first time. This was done by carefully matching the conditions inside the analytical and preparative column with each other. The results could therefore provide the industry with key knowledge for further implementation of SFC.

  • 218.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Gyllenhaal, Olle
    Computer-assisted optimization in preparative SFC, Challenges, Pitfalls and Solutions2010Conference paper (Refereed)
    Abstract [en]

    Preparative packed column SFC (pSFC) is an environmentally favorable alternative to normal phase HPLC. We are participating in a larger research project where the overreaching goal is to make an impact in the recovery of high-value compounds from agricultural byproducts and waste materials using environmentally sustainable techniques. Our specific task is to isolate large amounts of valuable compounds from discarded biomaterials using pSFC. It is still not possible to accurately model, simulate and optimize a preparative SFC proess, although SFC has been in use for almost fifty years. This is mainly because of the compressibility of the mobile phase and how this influences the physical parameters of the system. More particular, if pSFC is operated under combinations of back pressures and flow rates that give negligible pressure drop, it has been demonstrated and implied, that the tools developed and used within HPLC, can be transferred and used successfully [1, 2]. However, when the pressure drop becomes noticeable, the induced density gradient significantly increases the complexity. An earlier study has clearly described the effect of this pressure gradient on the retention factor, and also the column efficiency [3]. However, it remains to be investigated how the entire adsorption isotherm depends on the density.In this study we will investigate the use of the inverse and the perturbation peak methods, originally developed within LC, to determine the nonlinear adsorption isotherm for i) negligible, and ii) non-negligible pressure drop conditions respectively. To do this, we will use a simple racemic substance and a cellulose based CSP with a column equipped with pressure sensors at the inlet and outlet. Using obtained parameters we will validate the methods by simulating the separation using a variable coefficient version of the Equilibrium-Dispersive model for cases i and ii. [1] S. Ottiger, J. Kluge, A. Rajendran , M. Mazzotti, J. Chromatogr., A 1162 (2007) 74-82[2] C. Wenda, A. Rajendran, J. Chromatogr., A 1216 (2009) 8750-8758[3]A. Rajendran, O. Kräuchi, M. Mazzotti, M. Morbidelli, J Chromatogr., A, 1092 (2005) 149-160[4] G. Guiochon, A. Felinger, D. G. Shirazi, A. M. Katti, Fundamentals of Preparative and Nonlinear Chromatography 2nd Ed, Elsevier Academic Press (2006).

  • 219.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Arnell, Robert
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Kaczmarski, Krzysztof
    A systematic investigation of algorithm impact in preparative chromatography with experimental verifications2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 5, p. 662-672Article in journal (Refereed)
    Abstract [en]

    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

  • 220.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Arnell, Robert
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Kaczmarski, Krzysztof
    Computer Assisted Optimization of Pharmaceutical Purification - The Impact of Algorithms and Experimental Approach2010Conference paper (Refereed)
    Abstract [en]

    Computer assisted process optimization of chromatographic separations requires the selection of computer algorithms and measurement of relevant parameters. In this study, we will investigate how the choice of algorithms and the number of performed initial experiments affect the estimated optimal separations conditions. We will focus on conditions typically encountered for slurry packing coated 20 µm CSP in large-scale columns used for pharmaceutical intermediate purification.Probably the most essential for parameters in this context are the adsorption isotherm parameters for the components. The rapid "inverse method" is commonly used and this method requires that one numerically solve the mass balance equations describing the chromatographic process. Here we thoroughly investigate how different algorithms that solve the Equilibrium-Dispersive (ED) mass balance equations will affect the estimated adsorption isotherm parameters.Furthermore, we will investigate and compare how different strategies affect the prediction of the optimal separation conditions. First, we will use a more rapid approach that requires a minimum of experiments and uses standard algorithms to estimate optimal conditions. Secondly, we will use a more exact approach that requires more experiments and uses more advanced simulation- and optimization algorithms

  • 221.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Kaczmarski, Krzysztof
    A systematic investigation on the accuracy of computer simulations for optical isomers in industrial settings2010Conference paper (Refereed)
    Abstract [en]

    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.

  • 222.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Determination of adsorption isotherms in supercritical fluid chromatography2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1312, p. 124-133Article in journal (Refereed)
    Abstract [en]

    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.

  • 223.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Uppsala University.
    Rova, Maria
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Örnskov, Eivor
    IMED Biotech Unit, Sweden.
    Schweikart, Fritz
    IMED Biotech Unit, Sweden.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Investigation of factors influencing the separation of diastereomers of phosphorothioated oligonucleotides2019In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 411, no 15, p. 3383-3394Article in journal (Refereed)
    Abstract [en]

    This study presents a systematic investigation of factors influencing the chromatographic separation of diastereomers of phosphorothioated pentameric oligonucleotides as model solutes. Separation was carried out under ion-pairing conditions using an XBridge C18 column. For oligonucleotides with a single sulfur substitution, the diastereomer selectivity was found to increase with decreasing carbon chain length of the tertiary alkylamine used as an ion-pair reagent. Using an ion-pair reagent with high selectivity for diastereomers, triethylammonium, it was found the selectivity increased with decreased ion-pair concentration and shallower gradient slope. Selectivity was also demonstrated to be dependent on the position of the modified linkage. Substitutions at the center of the pentamer resulted in higher diastereomer selectivity compared to substitutions at either end. For mono-substituted oligonucleotides, the retention order and stereo configuration were consistently found to be correlated, with Rp followed by Sp, regardless of which linkage was modified. The type of nucleobase greatly affects the observed selectivity. A pentamer of cytosine has about twice the diastereomer selectivity of that of thymine. When investigating the retention of various oligonucleotides eluted using tributylammonium as the ion-pairing reagent, no diastereomer selectivity could be observed. However, retention was found to be dependent on both the degree and position of sulfur substitution as well as on the nucleobase. When analyzing fractions collected in the front and tail of overloaded injections, a significant difference was found in the ratio between Rp and Sp diastereomers, indicating that the peak broadening observed when using tributylammonium could be explained by partial diastereomer separation.

  • 224.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    A Deeper Understanding of a Complex Adsorption Behavior in a Common Chiral, Separation System2011Conference paper (Refereed)
    Abstract [en]

    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.

  • 225.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    A thermodynamic and kinetic study of an unusual adsorption behavior-Methyl Mandelate on commercially available Tris-(3,5- dimethylphenyl)carbamoyl Cellulose Chiral Stationary Phase2012Conference paper (Other academic)
    Abstract [en]

    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

  • 226.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Characterization of the Adsorption of Racemic Methyl Mandelate on Tris-(3,5-dimethylphenyl)carbamoyl Cellulose Chiral Stationary Phase2011Conference paper (Refereed)
    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.

  • 227.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    On the Reproducibility between Different Modern Supercritcal Fluid Chromatographic Systems2013Conference paper (Other academic)
    Abstract [en]

    Three different, commercially available, Supercritical Fluid Chromatography (SFC) systems were investigated: Thar Super Pure Discovery Series SFC, Waters UPC2 and Agilent 1260 Infinity SFC. The reason for choosing the two analytical systems from Agilent and Waters is that they represent two of the latest commercial systems available while the semi-preparative instrument was added to widen the study to include instruments also used for preparative purposes. With identical operational conditions set these systems were used to acquire analytical retention data and adsorption isotherms from overloaded injections. The investigation was limited to the use of methanol as modifier and operational conditions, temperature and back pressure most typically observed when utilizing SFC to separate polar compounds. The results clearly show that both analytical retention times and elution profiles are system dependent. Since the overloaded elution profiles are system dependent the adsorption isotherm will also be different. However, this do not mean that the adsorption is different, instead this it is due to the fact that identical instrumental settings, especially pressure and modifier composition settings, does not necessarily mean that the conditions inside the column are identical. This means that it is not possible to transfer an established separation method from one system to another, even if one is using the same column and identical instrument settings. Understanding of SFC-systems will be of fundamental importance for successful transfer of methods between systems, reliable adsorption isotherm determination, and analytical quality work and scaling up from analytical to preparative mode. These issues can probably be solved by measuring mass flow, pressure and temperature along the column, together with a sound understanding of the density variations of the mobile phase. However, the work of finding acceptable applications or guidelines to remove the tedious need for these measurements is currently investigated in our lab. This is a contribution from the Fundamental Separation Science Group www.FSSG.se

  • 228.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Using Modern SFC Systems for Adsorption Characterization2013Conference paper (Other academic)
    Abstract [en]

    Recently the pharmaceutical industry has started to replace preparative HPLC with preparative SFC to lower the environmental impact and to increase 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 isotherm data over a broad concentration range. If properly processed, this data gives not only correct information about the degree of heterogeneity but also the energy of interactions and mono layer capacities of each individual type of adsorption site in the phase system. Ultimately, this can result in identification of the types of interactions, i.e., dipole-dipole, van der Waals interactions etc. In this study we will present transfer of selected adsorption characterization methods, traditionally applied with success in LC, to SFC. We have here transferred all available knowledge from LC – from model selection to validation. We will also, using recent findings, explain the effects of pressure and temperature variations as well as how to accurately measure the volumetric flow rate on a modern analytical SFC system. We will demonstrate how the latest SFC instruments, with some critical modifications; have the potential for rapid and reliable acquisition of thermodynamic data using the ECP method. Finally we will elaborate on how the adsorption depends on density, temperature and modifier content in the mobile phase. This is a contribution from the Fundamental Separation Science Group www.FSSG.se

  • 229.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Preparative Separation of Chiral Pharmaceutical Compounds - The Effects of Packing Particle Size, Pressure Limit and Column Geometry on Productivity and Solvent Consumption2011Conference paper (Refereed)
    Abstract [en]

    In this study, omeprazole was used as a model compound. Omeprazole and other related sulfoxidebenzimidazolesare used against gastric ulcersand have been extensively studied regarding chromatographic resolution techniques using several different chiral stationary phases.First, AstraZeneca launched Losec, a racemic mixture of RS-omeprazole. Facing loss of patent, the more potent S-enantiomer was developed and marketed as Nexium. Now the patent of Nexium is close expiration why methods for isolation of the pure S-enantiomer will be of importance for the generic pharmaceutical companies.The experimental model separation system represents a system with good selectivity and high solubility of the solute in the eluent. In this investigation the productivity optima for three different particle sizes (5, 10 and 25 µm) at maximum system pressure ranging from 50 to 400 bars are studied. Two different optimizations cases were studied in depth. First,a process optimization with fixed column geometry is studied. The results clearly show that larger packing materials have higher productivity at low pressure drops on the analytical size column.With increasing allowed pressure drops, over 200 bar, the smaller packing materials have substantially higher productivity. The results also show that smaller packing material will always have much lower solvent consumption compared to larger particles.The second process optimization was performed with a fixed column volume, but the column geometry was variable. The results shows that the productivity obtained for the smaller packing particles materials was higher compared to the large for all allowed pressure drops. The productivity obtained for the small particle compared to the large increased by 25-300 % while maintaining 50-300 % less solvent consumption for the purification of the first enantiomer.The addition of TEA seems to be unfavorable for all tested conditions.In conclusion, the optimization of the enantioseparation of omeprazole has been shown to be dependent on column packing particle size as well as column geometry. It has been demonstrated that all parameters need to be simultaneously optimized to reach a global productivity optima.

  • 230.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Preparative Separation of Omeprazole: Predictions of the Optimal Experimental Conditions by Computer Simulations2011Conference paper (Refereed)
    Abstract [en]

    In this study, omeprazole was used as a model compound. Omeprazole and other related sulfoxide benzimidazoles are used against gastric ulcers and have been extensively studied regarding chromatographic resolution techniques using several different chiral stationary phases.First, AstraZeneca launched Losec, a racemic mixture of RS-omeprazole. Facing loss of patent, the more potent S-enantiomer was developed and marketed as Nexium. Now the patent of Nexium is close expiration why methods for isolation of the pure S-enantiomer will be of importance for the generic pharmaceutical companies.The experimental model separation system represents a system with good selectivity and high solubility of the solute in the eluent. In this investigation the productivity optima for three different particle sizes (5, 10 and 25 µm) at maximum system pressure ranging from 50 to 400 bars are studied. Two different optimizations cases were studied in depth. First,a process optimization with fixed column geometry is studied. The results clearly show that larger packing materials have higher productivity at low pressure drops on the analytical size column.With increasing allowed pressure drops, over 200 bar, the smaller packing materials have substantially higher productivity.The results also show that smaller packing material will always have much lower solvent consumption compared to larger particles.The second process optimization was performed with a fixed column volume, but the column geometry was variable. The results shows that the productivity obtained for the smaller packing particles materials was higher compared to the large for all allowed pressure drops. The productivity obtained for the small particle compared to the large increased by 25-300 % while maintaining 50-300 % less solvent consumption for the purification of the first enantiomer.The addition of TEA seems to be unfavorable for all tested conditions.In conclusion, the optimization of the enantioseparation of omeprazole has been shown to be dependent on column packing particle size as well as column geometry. It has been demonstrated that all parameters need to be simultaneously optimized to reach a global productivity optima.

  • 231.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Undin, Torgny
    A Deeper Investigation of Strange Preparative Band Shapes of a Simple Racemic Solute on tris-(3, 5- dimethylphenyl)carbamoyl Cellulose as Chiral Stationary Phase2011Conference paper (Refereed)
    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

  • 232.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Forss, Erik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Investigation of plateau methods for adsorption isotherm determination in supercritical fluid chromatography2014In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1354, p. 129-138Article in journal (Refereed)
    Abstract [en]

    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.

  • 233.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enantioseparation of omeprazole effect of different packing particle size on productivity2012In: Journal of Chromatography A, ISSN 0021-9673, Vol. 1240, no 1, p. 123-131Article in journal (Refereed)
    Abstract [en]

    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.

  • 234.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Högblom, Joakim
    Eka Chemicals.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Adsorption Isotherm Determination for Reliable Phase System Characterization in SFC: Challenges and Pitfalls2012Conference paper (Refereed)
    Abstract [en]

    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

  • 235.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Undin, Torgny
    Uppsala University Analytisk Kemi.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Characterization of an unusual adsorption behavior of racemic methyl-mandelate on a tris-(3,5-dimethylphenyl) carbamoyl cellulose chiral stationary phase2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 38, p. 6688-6696Article in journal (Refereed)
    Abstract [en]

    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.

  • 236.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Åsberg, Dennis
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    The Effect of Temperature, Pressure and Co-Solvent on a Chiral Supercritical Fluid Chromatography Separation2014In: Chromatography Today, ISSN 1752-8070, Vol. 7, no 3, p. 14-17Article in journal (Refereed)
  • 237.
    Enmark, Martin
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Åsberg, Dennis
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Shalliker, Andrew
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    A closer study of peak distortions in supercritical fluid chromatography as generated by the injection2015In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1400, p. 131-139Article in journal (Refereed)
    Abstract [en]

    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.

  • 238.
    enqvist, johanna
    Karlstad University, Faculty of Technology and Science.
    Koronabehandling av polymerbelagd kartong:  Inverkan av process och lagringstid på ytegenskaper och ytkemi hos koronabehandlat polymerbelagt kartong material2009Student thesis
    Abstract [sv]

    Det här arbetet har utförts som ett 30 hp examensarbete för kemiingenjörsutbildning på Karlstads universitet åt Stora Enso, Forshaga. Syftet var att undersöka koronabehandlingens effekt på plastbelagda kartongytor. Frågor som hur effekten minskar under lagringstid, om effekten påverkas av materialets bredd, tjocklek, pigment i plasten samt kylvalsarnas påverkan skulle undersökas.

     

    Största delen i arbetet var att undersöka hur ytenergin på behandlad plastbelagd kartong minskar med tiden och om detta varierar beroende på behandlingsgraden. Resultaten visade som väntat att ytenergin sjunker med tiden och ju högre ytenergin var direkt efter behandlingen desto fortare sjunker den. Direkt efter behandlingen varierade värdena ganska mycket men efter ca en vecka så verkade ytan ha "lugnat sig" (antagligen hade antalet laddningar som fanns på ytan direkt efter behandlingen då minskat). Ytenergin sjunker snabbast under den första månaden och sedan börjar kurvan plana ut. Efter ca två månader är nivån ganska stabil. Vid jämförelse av olika bredder gick det att se små skillnader som visade att breda rullar kräver mindre effekt för att nå ett visst dyntal än vad en smalare rulle gör. Samtidigt gick det att se att rullarna tycks ha något lägre ytenergi i kanten av rullarna än vad de har i mitten, men inte heller här handlar det om några stora skillnader.

     

    Arbetet innefattade även ett test för jämförelse av olika ytvikter på kartongen och det visade sig att ett tjockt material kräver mer energi vid behandlingen än ett tunnare, men skillnaden är liten. Det gick även att se skillnader vid jämförelsen av rullar som belagts med pigmenterad plast och de som belagts med transparent. Polyetylen med pigment i kräver lite högre effekt vid behandlingen för att kunna nå upp till lika hög ytenergi som samma material belagd med transparent plast.

     

    Det sista testet som skulle visa om det finns skillnader mellan matt och blank kylvals visade att olika kylvalsar gav olika ytråhet, men skillnaden mellan valsarna blir större på en ytrå yta än på en slät yta. Det var stora skillnader mellan valsarna om de jämfördes på dekorsidan, men på mer ytråa insidan verkade inte kylvalsen ha lika stor inverkan.

     

  • 239.
    Eriksson, Björn
    Karlstad University, Division for Chemistry.
    In-line application of electric fields in capillary separation systems2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The magnitude of an electric field possible to apply in a capillary separation system is limited, because a high electric field causes a too high current through the capillary. Application of the electric field in-line will give an increased conductivity in the column, further increasing the risk of too high currents. The conductivity changes were found to result from an overall increase in ionic strength within the electric field. The increase in ionic strength is caused by the increase in mobile phase ions with electrophoretic velocity against the flow, together with OH- or H3O+ ions (depending on polarity) formed at the inlet electrode. Further it was found that the use of a pressurized reservoir or splitting of the flow at the inlet electrode could significantly limit the conductivity changes and thereby the maximum applicable electric field strengths could be increased.

  • 240. Eriksson, Björn
    et al.
    Andersson, M.B.O.
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Deviation from Ohm's law in electric field assisted capillary liquid chromatography2003In: J. Chromatogr. A, 1010 (2003) 17-24Article in journal (Refereed)
  • 241. Eriksson, Björn
    et al.
    Andersson, M.B.O.
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Flow splitting at the inlet electrode as a method for increasing the usable electric field in electric field assisted capillary liquid chromatography2006In: J. Chromatogr. A, J. Chromatogr. A, 1119 (2006) 170-175Article in journal (Refereed)
  • 242. Eriksson, Björn
    et al.
    Dahl, Magnus
    Andersson, M.B.O.
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Changes in mobile phase ion distribution when combining pressurized flow and electric field2004In: Electrophoresis, 25 (2004) 3092-3097Article in journal (Refereed)
  • 243. Eriksson, Björn O.
    et al.
    Skuland, Inger Lill
    Andersson, Magnus B.O.
    Blomberg, Lars G
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    In-line application of electric field in capillary separation systems, Part II, Separation parameters affecting the conductivity2006In: Karlstad University Press, 2006:55, 2006Chapter in book (Other academic)
  • 244.
    Eriksson, Björn
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Skuland, Inger Lill
    Karlstad University, Faculty of Technology and Science.
    Andersson, Magnus
    Blomberg, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    In-line application of electric field in capillary separation systems Part II: Separation parameters affecting the conductivity2006Manuscript (preprint) (Other academic)
  • 245.
    Eriksson, Björn
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Skuland, Inger Lill
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Marlin, Nicola
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Andersson, Magnus
    Early Development, Pharmaceutical and Analytical Research & Development, AstraZeneca, Sweden.
    Blomberg, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    In-line application of electric field in capillary separation systems Part I: Joule heating, pH and conductivity2008In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 75, no 1, p. 83-90Article in journal (Refereed)
    Abstract [en]

    This study concerns the technique electric field-assisted capillary liquid chromatography. In this technique, an electric field is applied over the separation capillary in order to provide an additional selectivity. In this technique, the electric field is applied in-line in the separation capillary and here the electric current is the factor limiting the magnitude of applied electric field. The influence of Joule heating and other factors on the current in such systems has been investigated.

    The temperature in the capillary was first measured within a standard CE set-up, as function of effect per unit of length. Then the same cooling system was applied to an in-line set-up, to replicate the conditions between the two systems, and thus the temperature. Thus Joule heating effects could then be calculated within the in-line system. It was found that for systems applying an electric field in line, the direct influence from Joule heating was only relatively small.

    The pH in the capillary was measured in the in-line set-up using cresol red/TRIS solutions as pH probe. Significant changes in pH were observed and the results suggested that electrolysis of water is the dominant electrode reaction in the in-line system. In summary, the observed conductivity change in in-line systems was found to be mainly due to the pH change by hydrolysis of water, but primarily not due the temperature change in the capillary column.

  • 246.
    Eriksson, Madelene
    Karlstad University, Faculty of Technology and Science.
    Barns tankar om de fysikaliska begreppen avdunstning och kondensation kopplat till fenomenet moln2006Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the dissertation is to find out about children´s thoughts and ideas about the concepts of evaporation and condensation connected to the phenomenon of clouds. To reach the aim of this work, individual semistructured interviews have been made with pupils in grade three. The result shows that the pupils used and could account for the concepts of evaporation to a greater extent than the concepts of condensation. The pupils found it easier to see the connection between evaporation and the formation of clouds than between condensation and the formation of clouds. The conclusion of this work will thus be that pupils have ideas about the water cycle and even if they did not understand the concepts completely and the connections between them, they have deeply rooted explanations of these phenomena.

  • 247. Evans, C
    et al.
    Partyka, M
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences. Karlstad University, Faculty of Technology and Science, Materials Science.
    Naphthalene Complexation by .beta.-Cyclodextrin: Influence of Added Short Chain Branched and Linear Alcohols2000In: J. Incl. Phenom. Mol. Recog., 2000, 38, 381-396Article in journal (Refereed)
  • 248. Evans, CH
    et al.
    De Feyter, S
    Viaene, L
    van Stam, Jan
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences. Karlstad University, Faculty of Technology and Science, Materials Science.
    De Schryver, FC
    Bimolecular Processes of .alpha.-Terthiophene in a .beta.-Cyclodextrin Environment: An Exploratory Study1996In: J. Phys. Chem., 1996, 100, 2129-2135Article in journal (Refereed)
  • 249.
    Evertsson, J.
    et al.
    Lund University.
    Bertram, F.
    Lund University.
    Zhang, Fan
    KTH.
    Rullik, L.
    Lund University.
    Merte, L. R.
    Lund University.
    Shipilin, M.
    Lund University.
    Soldemo, Markus
    KTH.
    Ahmadi, Sareh
    KTH.
    Vinogradov, N.
    ESRF, France.
    Carla, F.
    ESRF, France.
    Weissenrieder, Jonas
    KTH.
    Götelid, Mats
    KTH.
    Pan, Jinshan
    KTH.
    Mikkelsen, A.
    Lund University.
    Nilsson, J. -O
    Sapa Technology, Sweden.
    Lundgren, E.
    Lund University.
    The thickness of native oxides on aluminum alloys and single crystals2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 349, p. 826-832Article in journal (Refereed)
    Abstract [en]

    We present results from measurements of the native oxide film thickness on four different industrial aluminum alloys and three different aluminum single crystals. The thicknesses were determined using X-ray reflectivity, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. In addition, atomic force microscopy was used for micro-structural studies of the oxide surfaces. The reflectivity measurements were performed in ultra-high vacuum, vacuum, ambient, nitrogen and liquid water conditions. The results obtained using X-ray reflectivity and X-ray photoelectron spectroscopy demonstrate good agreement. However, the oxide thicknesses determined from the electrochemical impedance spectroscopy show a larger discrepancy from the above two methods. In the present contribution the reasons for this discrepancy are discussed. We also address the effect of the substrate type and the presence of water on the resultant oxide thickness.

  • 250.
    Filipsson Lopez, Nicolina
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies.
    Vi ska koka soppa, is-soppa!: En observationsstudie om förskolebarns meningsskapande kring aggregationsformer som lärande objekt.2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this study is to see the perceptions that preschool children have about the aggregate states as a phenomena through some simple activities with ice (solid), water (liquid form) and water vapor (gas form) and how the children create meaning through the aggregate states. The theoretical perspective in this study is development pedagogic, a part of phenomenography. The used method is qualitative observation in a preschool group and the data is collected with notes. The children have been observed during two different activities; an experiment, From Ice to Vapor and a game, the Molecular game. The experiment took place twice, one time before the game and one time after. 19 children in the ages 4-6 years have been part of this study. The results show a movement of the conversation from the first experiment when they talked a lot about earlier experiences of water to the last experiment when the conversation was more about molecules. The children changed their perceptions in the meeting with the activities and they created meaning in relation to the aggregate states. The study also shows that the new experiences that the children receive through the activities are helping them with their perception of the object of learning, the aggregate states.

    This study gives preschool teachers an understanding of how children are creating meaning about aggregate states and how understanding of chemistry can take place in preschool. 

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