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  • 1.
    Antonsson, Cecilia
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Mjölk, gluten och ADHD: En litteraturundersökning om mjölk och glutens påverkan hos barn med ADHD2014Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Attention Deficit Hyperactivity Disorder (ADHD) is becoming a more common diagnosis of younger children. In recent years the perception that some ingredients in our food may have a negative effect regarding the symptoms in children with ADHD has grown stronger. Children with ADHD often suffer from irritated bowel syndromes which affect their ability to digest food. This may result in malnutrition as well as a release of substances that are harmful.The purpose of this report is to compile and illustrate the knowledge of how special food, particular milk protein and gluten, may affect the symptoms of children with ADHD. Also, the report aims to evaluate if there should be changes made in Kindergarten to increase the well-being of these children. The report is a summary of research results on the effects milk protein and gluten have on children with ADHD.The majority of children with ADHD demonstrate decreased symptoms if they receive a diet without milk protein and gluten.If children with ADHD would be given a special diet excluding milk protein and gluten it is realistic to assume that their ADHD-symptoms might be reduced with a greater sense of well-being and quality of life as a result.

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    Examensarbete
  • 2.
    Bermúdez, Eduardo
    et al.
    Universidad de la Republic, URY.
    Ventura, Oscar N
    Universidad de la Republic, URY.
    Saenz Mendez, Patricia
    Universidad de la Republic, URY.
    Mechanism of the organocatalyzed decarboxylative Knoevenagel-Doebner reaction. A theoretical study.2010In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, no 50, p. 13086-92Article in journal (Refereed)
    Abstract [en]

    We have investigated important intermediates and key transition states of the organocatalyzed Knoevenagel condensation using density functional theory and two different basis sets (6-31 G(d,p) and 6-311++G(2df,2pd)), both in gas phase and simulating the bulk solvent (pyridine) using the PCM method. Calculated structures for reactants, intermediates, and key transition states suggest that the secondary amine catalyst is essential, both for activating the aldehyde for nucleophilic attack, and in the possible decarboxylation pathways. The calculated results are shown to agree with available experimental information. On the basis of the results obtained, the studied mechanism may be important in the understanding of vinylphenol production during malting and brewing of wheat and barley grains.

  • 3.
    Brovetto, Margarita
    et al.
    Universidad de la Republic, URL.
    Gamenara, Daniela
    Universidad de la Republic, URL.
    Saenz Mendez, Patricia
    Universidad de la Republic, URL.
    Seoane, Gustavo A.
    Universidad de la Republic, URL.
    C-C Bond-Forming Lyases in Organic Synthesis2011In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 111, no 7, p. 4346-4403Article, review/survey (Refereed)
  • 4.
    Cerecetto, H
    et al.
    Universidad de la República, URY.
    Dias, E
    Universidad de la República, URY.
    Di Maio, R
    Universidad de la República, URY.
    Gonzalez, M
    Universidad de la República, URY.
    Pacce, S
    Universidad de la República, URY.
    Saenz Mendez, Patricia
    Universidad de la República, URY.
    Seoane, G
    Universidad de la República, URY.
    Suescun, L
    Universidad de la República, URY.
    Mombru, A
    Universidad de la República, URY.
    Fernandez, G
    Universidad de la República, URY.
    Lema, M
    Universidad de la República, URY.
    Villalba, J
    Universidad de la República, URY.
    Synthesis and herbicidal activity of N-oxide derivatives2000In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 48, no 7, p. 2995-3002Article in journal (Refereed)
    Abstract [en]

    As part of an ongoing program on the chemistry and biological activity of N-oxide-containing molecules, a number of novel 1,2,5-oxadiazole N-oxide, benzo[1,2-c]1,2,5-oxadiazole N-oxide, and quinoxaline N,N'-dioxide derivatives were synthesized and evaluated for their herbicidal activity. Many of these compounds exhibited moderate to good herbicidal pre-emergence activity against Triticum aestivum. Dose-response studies were done on the more representative compounds (12, 20, and 26). The most active compound, butylcarbamoylbenzo[1,2-c]l,2,5-oxadiazole N-oxide, 26, displayed herbicidal activity at concentrations as low as 24 g/ha.

  • 5.
    Christophliemk, Hanna
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Koskinen, Ari M.P.
    An Improved Synthesis of the C1-C9 -fragment of Calyculin C.1997Conference paper (Other academic)
  • 6.
    Dabrowski, Patrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Rening av rökgaskondensat i ett fjärrvärmeverk: Återanvändning av rökgaskondensat som spädvatten2017Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    Arvika Fjärrvärme AB is manufacturing and distributing district heating to around 300 customers in Arvika. Heat production consists of a BFB boiler fed with GROT fuel (branches and peaks) and delivers a maximum power of 30 MW. In order to operate the plant, an average of 60 m3 of water per day is consumed from the urban water network. The water consumption is divided between water treatment, sooting and process cooling.

    In the processes, sulfur is dosed to obtain a more complete combustion of the hazardous flue gases that can occur. This is a result of previous thesis made for Arvika fjärrvärme. GROT is a fuel that contains high levels of moisture, which means that a high amount of condensate is formed during combustion, averaging 100 m3 per day. At present, condensate is sufficient to meet the condensate limit values ​​to be flushed into the drain. This is achieved by sand filtration and pH neutralization.

    Today, Arvika heat production is equipped with a purification stage for the feed water consisting of a softening filter and membrane filtration. This creates good conditions for cleaning the condensate and recirculating it in the process. Questions for this study are which hazardous substances the condensate can contain and how the condensate composition affected due to sulfur dosage. In addition, Arvika fjärrvärme wants to find out whether the purified condensate can replace the use of the urban water and, finally, if the condensate can be purified and used as feed water in the process.

    The execution of the work was based on a full-scale attempt in two operating cases of 9 and 18 MW. The tank collecting all condensate after purification in the sand filter and pH neutralization was coupled to the feed water purification stage. Thus, the condensate was pumped and purified in the softening filter and membrane filter. Assay substrates were collected before and after purification of the condensate.

    In addition to the topics that Arvika investigates, high levels of alkalinity were found in the condensate. The sulfur dosage that Arvika technology works with can be the cause of the high concentrations of sulphate. However, it appears that both the sulfate and alkalinity were purified in the membrane filter.

    The amount of condensate formed cannot completely replace the entire water requirement, but definitely large parts. The condensate can be used as feed water based on the retention rate for all substances. However, it appears that two substances, chloride and sulphate can create problems for the membrane filter. To investigate this, the condensate should be tested over a longer period of time to see the affect the chloride as well as the sulphate in the long run.

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  • 7.
    Forssén, Patrik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Multia, Evgen
    University of Helsinki, Finland.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Andersson, Marie
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Aastrup, Teodor
    Attana AB, Sweden.
    Altun, Samuel
    Attana AB, Sweden.
    Wallinder, Daniel
    Attana AB, Sweden.
    Wallbing, Linus
    Attana AB, Sweden.
    Liangsupree, Thanaporn
    University of Helsinki, Finland.
    Riekkola, Marja-Liisa
    University of Helsinki, Finland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Reliable Strategy for Analysis of Complex Biosensor Data2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 8, p. 5366-5374Article in journal (Refereed)
    Abstract [en]

    When using biosensors, analyte biomolecules of several different concentrations are percolated over a chip with immobilized ligand molecules that form complexes with analytes. However, in many cases of biological interest, e.g., in antibody interactions, complex formation steady-state is not reached. The data measured are so-called sensorgram, one for each analyte concentration, with total complex concentration vs time. Here we present a new four-step strategy for more reliable processing of this complex kinetic binding data and compare it with the standard global fitting procedure. In our strategy, we first calculate a dissociation graph to reveal if there are any heterogeneous interactions. Thereafter, a new numerical algorithm, AIDA, is used to get the number of different complex formation reactions for each analyte concentration level. This information is then used to estimate the corresponding complex formation rate constants by fitting to the measured sensorgram one by one. Finally, all estimated rate constants are plotted and clustered, where each cluster represents a complex formation. Synthetic and experimental data obtained from three different QCM biosensor experimental systems having fast (close to steady-state), moderate, and slow kinetics (far from steady-state) were evaluated using the four-step strategy and standard global fitting. The new strategy allowed us to more reliably estimate the number of different complex formations, especially for cases of complex and slow dissociation kinetics. Moreover, the new strategy proved to be more robust as it enables one to handle system drift, i.e., data from biosensor chips that deteriorate over time.

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    fulltext
  • 8.
    Franco, Leandro R.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Cardenuto, Marcelo Hidalgo
    Cidade Universitária, Brazil.
    Unraveling the Impact of Flexibility and Solvent Effects on the UV-Vis Absorption Spectrum of Subphthalocyanine in Liquid Chloroform within the Born-Oppenheimer Molecular Dynamics Approach2023In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 127, no 38, p. 7937-7942Article in journal (Refereed)
    Abstract [en]

    A study based on Born-Oppenheimer molecular dynamics (BOMD) of the subphthalocyanine (SubPc) with a chloride attached to the central boron atom was carried out. The BOMD simulation is used to access the dynamic evolution of the SubPc in liquid chloroform, and the electronic absorption spectrum is calculated using the Time-Dependent Density Functional Theory (TDDFT) considering explicit solvent models. We show that the conformational changes and solvent effects produce a red shift of the Q-band, where the largest contribution is due to the geometry changes of the symmetric structure of SubPc. A large splitting (0.2 eV) of the first electronic transition is also described, and it originates as a shoulder in the Q-band, which according to previous experimental studies is attributed to a vibronic origin. The red shift is obtained in agreement with experiment within less than 0.1 eV. The splitting is a consequence of the symmetry breaking in the SubPc central ring structure occurring during the molecular dynamics, with a significant contribution to the large red shift and the broadening of the spectrum.

  • 9.
    Gamenara, D.
    et al.
    Universidad de la Republic, URY.
    Seoane, G. A.
    Universidad de la Republic, URY.
    Saenz Mendez, Patricia
    Universidad de la Republic, URY.
    Dominguez de Maria, P
    RWTH Aachen University, DEU.
    Redox Biocatalysis: Fundamentals and Applications2012Book (Other academic)
  • 10.
    Gamenara, Daniela
    et al.
    Universidad de la Republica, URY.
    Saenz Mendez, Patricia
    Universidad de la Republica, URY.
    Seoane, Gustavo
    Universidad de la Republica, URY.
    Dominguez de Maria, Pablo
    RWTH Aachen University, DEU.
    Ionic Liquids as (Co-)Solvents for Nonhydrolytic Enzymes2012In: Ionic Liquids as (Co-)Solvents for Nonhydrolytic Enzymes / [ed] Pablo Domínguez de María, John Wiley & Sons, Ltd , 2012, p. 229-259Chapter in book (Other academic)
    Abstract [en]

    Summary This chapter contains sections titled: Nomenclature of ILs Ionic Liquids and Nonhydrolytic Enzymes Use of ILs in Oxidoreductase-Catalyzed Enzymatic Reactions ILs in Lyase-Catalyzed Reactions Prospects References

  • 11.
    Lord, Sandra
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Study of yield variation in a pharmaceutical manufacturing process and optimization of purification subsection: By a design of experiments study of the production parameters and a laboratory study of the purification step2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The product R1-MR2E is an ester formed from an esterification of a carboxylic acid and an alcohol at Cambrex Karlskoga AB. The production of the intermediate R1-MR2E is a large-scale production and there are two main objectives and two sub-objectives that this project aims to study of the manufacturing.The manufacturing of R1-MR2E experience big variations in the product yield which is affecting theproductions stability and economic aspects of it. Thus, one of the main objectives in this project was to use experimental design to find significant factors that causes yield variations. The results from this study showed five significant factors that affect the yield positively or negatively by resulting in higher or lower product weight. The factors found are the amount of charged toluene solution containing the by-product R1-DR2E from the recycling system, the amount of charged carboxylic acid, the reaction time, the amount of added Na2SO3 in the neutralisation step and the regulated pH value after the crystallisation step. The other main objective is to optimize the purification sub-section using activated carbon (AC). There are two sub-objectives for this part of the study where the first sub-objective is to evaluate how much activated carbon that is needed to remove the impurities and colouration in the product. The second sub-objective is to investigate if an activated carbon filter could be used as a substitute for the commonly used loose powder activated carbon. To answer this objective a laboratory method was used, where the large-scale purification- and crystallisation step as well as after treatment were scaled down to lab scaleand then experiments were conducted to determine the effects of different amounts of activated carbon, using no carbon, and utilizing another type of activated carbon known as activated carbon filters. The results were then analysed for colour and purity by a visual observation method and High-Performance Liquid Chromatography (HPLC) method. The conclusion from this study is that only 25% of the amount of activated carbon used today is needed to remove the colouration in the product. The activated carbon did not completely remove the impurities in the product. The other conclusion was that the idea that the activated carbon removed the small impurities was wrong, and the levels of the impurities are already small enough in the large-scale production that the purification step is not needed to reach approved levels of these impurities. The activated carbon filter also works to remove the colouration with only one filtration but does not work well on removing the impurities in the product. 

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    Study of yield variation in a pharmaceutical manufacturing process and optimization of purification subsection
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    Arkivfil
  • 12.
    Risso, Mariela
    et al.
    University of the Republic, URY.
    Mazzini, Mauro
    University of the Republic, URY.
    Kroeger, Santiago
    University of the Republic, URY.
    Saenz Mendez, Patricia
    University of the Republic, URY.
    Seoane, Gustavo
    University of the Republic, URY.
    Gamenara, Daniela
    University of the Republic, URY.
    Microwave-assisted solvent-free lipase catalyzed transesterification of beta-ketoesters2012In: Green Chemistry Letters and Reviews, ISSN 1751-8253, E-ISSN 1751-7192, Vol. 5, no 4, p. 539-543Article in journal (Refereed)
    Abstract [en]

    Lipase-catalyzed transesterification was used as an efficient tool for the interconversion of beta-ketoesters. Catalytic activity of commercial lipase B from Candida antarctica (Novozym 435) was evaluated in systems involving non activated acyl donors, and enhanced using microwave irradiation. Interestingly, the combination of CAL B in microwave irradiation worked excellent in solvent-free conditions, thus assuring a highly competitive and environment-friendly process with high yields (up to 96%) in competitive times (< 2h). The combination of biocatalysis with solvent-free systems and microwave assistance is currently scarcely used, and may represent a powerful synergy for preparative reactions.

  • 13.
    Vera, C. M.
    et al.
    Phenomenex Australia, Pty Ltd, Lane Cove, NSW 2067, Australia.
    Shock, D.
    Phenomenex Australia, Pty Ltd, Lane Cove, NSW 2067, Australia.
    Dennis, G. R.
    Australian Centre for Research on Separation Science, School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Enmark, Martin
    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).
    Shalliker, R. Andrew
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Australian Centre for Research on Separation Science, School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
    A preliminary study on the selectivity of linear polynuclear aromatic hydrocarbons in SFC using phenyl-type stationary phases2015In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 121, p. 136-140Article in journal (Refereed)
    Abstract [en]

    The retention behaviour of a homologous series of polyaromatic hydrocarbons was evaluated on two phenyl-type stationary phases in reversed phase supercritical fluid chromatography (SFC). These phases were the Synergi polar-RP phase and the Cosmosil 5PBB phase, both of which are polar end-capped and incorporate an ether in a propyl chain that tethers the phenyl ring to the silica surface. The Cosmosil 5PBB phase also has five bromine atoms on the phenyl ring. The retention capacity of the Cosmosil column was substantially greater than the Synergi column. However, selectivity on the Cosmosil column was effectively independent of the acetonitrile modifier composition in the CO2 mobile phase, whereas, selectivity on the Synergi column was greatly affected by the acetonitrile modifier in the CO2 mobile phase. The results from this study showed that selectivity and retention studies in HPLC cannot be used to predict selectivity and retention behaviour in SFC. (C) 2015 Elsevier B.V. All rights reserved.

  • 14.
    Wu, Jingnan
    et al.
    Chalmers University of Technology, Sweden; Aalborg University, Denmark.
    Ling, Zhaoheng
    King Abdullah University of Science & Technology, Saudi Arabia.
    Franco, Leandro R.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Jeong, Sang Young
    Korea University, South Korea.
    Genene, Zewdneh
    Chalmers University of Technology, Sweden.
    Mena, Josue
    Chalmers University of Technology, Sweden.
    Chen, Si
    King Abdullah University of Science & Technology, Saudi Arabia.
    Chen, Cailing
    King Abdullah University of Science & Technology, Saudi Arabia.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Marchiori, Cleber
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Kimpel, Joost
    Chalmers University of Technology, Sweden.
    Chang, Xiaoming
    King Abdullah University of Science & Technology, Saudi Arabia.
    Isikgor, Furkan H. H.
    King Abdullah University of Science & Technology, Saudi Arabia.
    Chen, Qiaonan
    Chalmers University of Technology, Sweden.
    Faber, Hendrik
    King Abdullah University of Science & Technology, Saudi Arabia.
    Han, Yu
    King Abdullah University of Science & Technology, Saudi Arabia.
    Laquai, Frederic
    King Abdullah University of Science & Technology, Saudi Arabia.
    Zhang, Maojie
    Shandong University, China.
    Woo, Han Young
    Korea University, South Korea.
    Yu, Donghong
    Aalborg University, Denmark.
    Anthopoulos, Thomas D. D.
    King Abdullah University of Science & Technology, Saudi Arabia.
    Wang, Ergang
    Chalmers University of Technology, Sweden.
    On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 %2023In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773Article in journal (Refereed)
    Abstract [en]

    The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular & pi;-& pi; interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.

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  • 15.
    Zaar, Felicia
    et al.
    Uppsala University, Sweden.
    Araujo, Moyses
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013). Uppsala University, Sweden.
    Emanuelsson, Rikard
    Uppsala University, Sweden.
    Stromme, Maria
    Uppsala University, Sweden.
    Sjodin, Martin
    Uppsala University, Sweden.
    Tetraphenylporphyrin electrocatalysts for the hydrogen evolution reaction: applicability of molecular volcano plots to experimental operating conditions2023In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 52, no 30, p. 10348-10362Article in journal (Refereed)
    Abstract [en]

    Recent years have seen an increasing interest in molecular electrocatalysts for the hydrogen evolution reaction (HER). Efficient hydrogen evolution would play an important role in a sustainable fuel economy, and molecular systems could serve as highly specific and tunable alternatives to traditional noble metal surface catalysts. However, molecular catalysts are currently mostly used in homogeneous setups, where quantitative evaluation of catalytic activity is non-standardized and cumbersome, in particular for multistep, multielectron processes. The molecular design community would therefore be well served by a straightforward model for prediction and comparison of the efficiency of molecular catalysts. Recent developments in this area include attempts at applying the Sabatier principle and the volcano plot concept - popular tools for comparing metal surface catalysts - to molecular catalysis. In this work, we evaluate the predictive power of these tools in the context of experimental operating conditions, by applying them to a series of tetraphenylporphyrins employed as molecular electrocatalysts of the HER. We show that the binding energy of H and the redox chemistry of the porphyrins depend solely on the electron withdrawing ability of the central metal ion, and that the thermodynamics of the catalytic cycle follow a simple linear free energy relation. We also find that the catalytic efficiency of the porphyrins is almost exclusively determined by reaction kinetics and therefore cannot be explained by thermodynamics alone. We conclude that the Sabatier principle, linear free energy relations and molecular volcano plots are insufficient tools for predicting and comparing activity of molecular catalysts, and that experimentally useful information of catalytic performance can still only be obtained through detailed knowledge of the catalytic pathway for each individual system.

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  • 16.
    Åsberg, Dennis
    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.
    Lesko, Marek
    Department of Chemical and Process Engineering, Rzeszów University of Technology, PL-35 959 Rzeszów, Poland.
    Cavazzini, Alberto
    Department of Chemical and Pharmaceutical Sciences, University of Ferrara, IT-44 121 Ferrara, Italy.
    Kaczmarski, Krzysztof
    Department of Chemical and Process Engineering, Rzeszów University of Technology, PL-35 959 Rzeszów, Poland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Method transfer from high-pressure liquid chromatography to ultra-high-pressure liquid chromatography. II. Temperature and pressure effects2015In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1401, p. 52-59Article in journal (Refereed)
    Abstract [en]

    The importance of the generated temperature and pressure gradients in ultra-high-pressure liquid chromatography (UHPLC) are investigated and compared to high-pressure liquid chromatography (HPLC). The drug Omeprazole, together with three other model compounds (with different chemical characteristics, namely uncharged, positively and negatively charged) were used. Calculations of the complete temperature profile in the column at UHPLC conditions showed, in our experiments, a temperature difference between the inlet and outlet of 16 degrees C and a difference of 2 degrees C between the column center and the wall. Through van't Hoff plots, this information was used to single out the decrease in retention factor (k) solely due to the temperature gradient. The uncharged solute was least affected by temperature with a decrease in k of about 5% while for charged solutes the effect was more pronounced, with k decreases up to 14%. A pressure increase of 500 bar gave roughly 5% increase in k for the uncharged solute, while omeprazole and the other two charged solutes gave about 25, 20 and 15% increases in k, respectively. The stochastic model of chromatography was applied to estimate the dependence of the average number of adsorption/desorption events (n) and the average time spent by a molecule in the stationary phase (tau(s)) on temperature and pressure on peak shape for the tailing, basic solute. Increasing the temperature yielded an increase in n and decrease in tau(s) which resulted in less skew at high temperatures. With increasing pressure, the stochastic modeling gave interesting results for the basic solute showing that the skew of the peak increased with pressure. The conclusion is that pressure effects are more pronounced for both retention and peak shape than the temperature effects for the polar or charged compounds in our study. (C) 2015 Elsevier B.V. All rights reserved.

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