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  • 51.
    Forssén, Patrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Edström, Lena
    Uppsala University.
    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.
    Injection profiles in liquid chromatography II: Predicting accurate injection-profiles for computer-assisted preparative optimizations2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 34, p. 5794-5800Article in journal (Refereed)
    Abstract [en]

    In computer assisted optimization of liquid chromatography it has been known for some years that it is important to use experimental injection profiles, instead of rectangular ones, in order to calculate accurate elution bands. However, the incorrectly assumed rectangular profiles are still mostly used especially in numerical optimizations. The reason is that the acquisition of injection profiles, for each injection volume and each flow rate considered in a computer-assisted optimization requires a too large number of experiments. In this article a new function is proposed, which enables highly accurate predictions of the injection profiles and thus more accurate computer optimizations, with a minimum experimental effort. To model the injection profiles for any injection volume at a constant flow rate, as few as two experimental injection profiles are required. If it is desirable to also take the effect of flow rate on the injection profiles into account, then just two additional experiments are required. The overlap between fitted and experimental injection profiles at different flow rates and different injection volumes were excellent, more than 90%, using experimental injection profiles from just four different injection volumes at two different flow rates. Moreover, it was demonstrated that the flow rate has a minor influence on the injection profiles and that the injection volume is the main parameter that needs to be accounted for.

  • 52.
    Forssén, Patrik
    et al.
    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).
    Impact of column and stationary phase properties on the productivity in chiral preparative LC2018In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 41, no 6, p. 1346-1354Article in journal (Refereed)
    Abstract [en]

    By generating 1500 random chiral separation systems, assuming two-site Langmuir interactions, we investigated numerically how the maximal productivity (P-R,P-max) was affected by changes in stationary phase adsorption properties. The relative change in P-R,P-max, when one adsorption property changed 10%, was determined for each system and for each studied parameter the corresponding productivity change distribution of the systems was analyzed. We could conclude that there is no reason to have columns with more than 500 theoretical plates and larger selectivity than 3. More specifically, we found that changes in selectivity have a major impact on P-R,P-max if it is below similar to 2 and, interestingly, increasing selectivity when it is above similar to 3 decreases P-R,P-max. Increase in relative saturation capacity will have a major impact on P-R,P-max if it is below similar to 40%, but only modest above this percent. Increasing total monolayer saturation capacity, or decreasing the first eluting enantiomer's retention factor, will have a modest effect on P-R,P-max and increased efficiency will have almost no effect at all on P-R,P-max unless it is below similar to 500 theoretical plates. Finally, we showed that chiral columns with superior analytic performance might have inferior preparative performance, or vice versa. It is, therefore, not possible to assess columns based on their analytical performance alone.

  • 53.
    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.

  • 54.
    Forssén, Patrik
    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.
    Relative importance of column and adsorption parameters on the productivity in preparative liquid chromatography. I: Investigation of a chiral separation system2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1299, p. 58-63Article in journal (Refereed)
    Abstract [en]

    Starting out from an experimental chiral separation system we have used computer simulations for a systematic investigation on how the maximum productivity depends on changes in column length, packing particle size, column efficiency, back pressure, sample concentration/solubility, selectivity, retention factor of the first eluting component and monolayer saturation capacity. The study was performed by changing these parameters, one at a time, and then calculating the corresponding change in maximum productivity. The three most important parameters for maximum production rate was found to be (i) the selectivity (ii) the retention factor of the first eluting component and (iii) the column length. Surprisingly, the column efficiency and sample concentration/solubility were of minor importance. These findings can be used as rough guidelines for column selection, e.g. a low-efficiency column are more likely perform better, in terms of productivity, than a high-efficiency column that have higher retention factor for the first eluting component.

  • 55.
    Forssén, Patrik
    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.
    Relative importance of column and adsorption parameters on the productivity in preparative liquid chromatography II: Investigation of separation systems with competitive Langmuir adsorption isotherms2014In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1347, p. 72-79Article in journal (Refereed)
    Abstract [en]

    In this study we investigated how the maximum productivity for commonly used, realistic separation system with a competitive Langmuir adsorption isotherm is affected by changes in column length, packing particle size, mobile phase viscosity, maximum allowed column pressure, column efficiency, sample concentration/solubility, selectivity, monolayer saturation capacity and retention factor of the first eluting compound. The study was performed by generating 1000 random separation systems whose optimal injection volume was determined, i.e., the injection volume that gives the largest achievable productivity. The relative changes in largest achievable productivity when one of the parameters above changes was then studied for each system and the productivity changes for all systems were presented as distributions. We found that it is almost always beneficial to use shorter columns with high pressure drops over the column and that the selectivity should be greater than 2. However, the sample concentration and column efficiency have very limited effect on the maximum productivity. The effect of packing particle size depends on the flow rate limiting factor. If the pumps maximum flow rate is the limiting factor use smaller packing, but if the pressure of the system is the limiting factor use larger packing up to about 40μm.

  • 56.
    Fredriksson, Robert
    et al.
    AkzoNobel , Separations Products, Bohus, Sweden.
    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).
    The Importance of Overloading Studies in Method Development: A Case Study2012Conference paper (Refereed)
  • 57.
    Friden, Mikael E.
    et al.
    Uppsala Univ, Dept Chem BMC, Analyt Chem, POB 599, S-75124 Uppsala, Sweden..
    Jumaah, Firas
    Lund Univ, Ctr Anal & Synth, Dept Chem, POB 124, S-22100 Lund, Sweden..
    Gustavsson, Christer
    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).
    Turner, Charlotta
    Lund Univ, Ctr Anal & Synth, Dept Chem, POB 124, S-22100 Lund, Sweden..
    Sjoberg, Per J. R.
    Uppsala Univ, Dept Chem BMC, Analyt Chem, POB 599, S-75124 Uppsala, Sweden..
    Samuelsson, Jorgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Evaluation and analysis of environmentally sustainable methodologies for extraction of betulin from birch bark with a focus on industrial feasibility2016In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 18, no 2, p. 516-523Article in journal (Refereed)
    Abstract [en]

    Betulin from birch bark was extracted using two principally different extraction methodologies - classical Reflux Boiling (RB) and Pressurized Liquid Extraction (PLE). The extraction methods were analyzed based on both recovery and purity as well as for RB industrial feasibility. The purity and recovery for the different extraction methods were analyzed using High Performance Liquid Chromatography (HPLC) coupled with three different detection principles: Diode Array Detection (DAD), Mass Spectrometry (MS) and Charged Aerosol Detection (CAD). The chromatographic purity was determined by all detections whereas the DAD was used also for complementary gravimetric calculations of the purity of the extracts. The MS detection (in MS and MS/MS modes) was mainly used to characterize the impurities. Two steps to increase the purity of RB extracts were evaluated - pre-boiling the bark in water and precipitation by adding water to the extract. Finally, the methods were compared in terms of amounts of betulin produced and solvent consumed. The RB method including a precipitation step produced the highest purity of betulin. However, results indicate that PLE using three cycles with the precipitation step gives similar purities as for RB. The PLE method produced up to 1.6 times higher amount of extract compared to the RB method. However, the solvent consumption (liter solvent per gram product) for PLE was around 4.5 times higher as compared to the classical RB. PLE performed with only one extraction cycle gave results more similar to RB with 1.2 times higher yield and 1.4 times higher solvent consumption. The RB process was investigated on an industrial scale using a model approach and several important key-factors could be identified. The most energy demanding step was the recycling of extraction solvent which motivates that solvent consumption should be kept low and calculations show a great putative energy reduction by decreasing the ethanol concentration used in the RB process to lower than 90%.

  • 58.
    Glenne, Emelie
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Leek, Hanna
    AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    Klarqvist, Magnus
    AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    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).
    Peak deformations in preparative supercritical fluid chromatography due to co-solvent adsorption2016In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1468, p. 200-208Article in journal (Refereed)
    Abstract [en]

    In supercritical fluid chromatography (SFC) the mobile phase comprises of carbon dioxide (CO2) as main solvent and smaller amounts of an organic polar solvent (often an alcohol) as co-solvent. The co-solvent is considered to function by changing the overall polarity of the eluent, i.e. by acting as a "modifier". However, recent studies indicate that the co-solvent methanol can also adsorb to some common SFC stationary phases. Hence, the co-solvent should also be able to function as an "adsorbing additive", i.e. an eluent component that competes with the injected solutes about the stationary phase surface. In this study it was found by fitting different mechanistic models to systematic experimental data, that the co-solvent methanol can have both functions: at low co-solvent fractions, methanol acts as an additive whereas at larger fractions it acts as a modifier. Moreover, it was found that when the co-solvent adsorbs more strongly to the stationary phase than the solute, "bizarre" deformations of the preparative band shapes can occur. This is illustrated by a solute that converts from a normal "Langmuirian" band shape to an "anti-Langmuirian" shape when changing from neat carbon dioxide (CO2) to an eluent containing co-solvent. This peak shape transition is dependent on both (i) the relative retention of the solute and co-solvent to the stationary phase in eluent containing neat CO2 and on (ii) the relative retention of the additive perturbation peak and the solute peak in eluent containing also co-solvent. 

  • 59.
    Glenne, Emelie
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Leek, Hanna
    AstraZeneca R&D, Innovat Med & Early Dev, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    Klarqvist, Magnus
    AstraZeneca R&D, Innovat Med & Early Dev, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    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).
    Systematic investigations of peak deformations due to co-solvent adsorption in preparative supercritical fluid chromatography2017In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1496, p. 141-149Article in journal (Refereed)
    Abstract [en]

    Strangely shaped overloaded bands were recently reported using a standard supercritical fluid chromatographic system comprising a diol column as the stationary phase and carbon dioxide with methanol as the mobile phase, Some of these overloaded elution profiles appeared strongly deformed and even had "anti-Langmuirian" shapes although their solute compounds had "Langmuirian" adsorption. To obtain a more complete understanding of the generality of these effects, the investigation was expanded to cover also other common co-solvents, such as ethanol, 2-propanol, and acetonitrile, as well as various stationary phase materials, such as silica, and 2-ethylpyridine. From this expanded study it could be confirmed that the effects of deformed overloaded solute band shapes, due to co-solvent adsorption, is general phenomena in supercritical fluid chromatographic. It could also be concluded that these effects as well as previously observed "solvent effects" or "plug effects" are entirely due to competition between the solute and solvent molecules for the adsorption sites on the stationary phase surface. Finally, guidelines were given for how to evaluate the risk of deformations occurring for a given solvent-column combination, based simply on testing retention times of solutes and co-solvent. (C) 2017 Elsevier B.V. All rights reserved.

  • 60.
    Glenne, Emelie
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Ohlen, Kristina
    AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    Leek, Hanna
    AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    Klarqvist, Magnus
    AstraZeneca R&D, Innovat Med, Resp Inflammat & Autoimmun, S-43183 Molndal, Sweden..
    Samuelsson, Jorgen
    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 methanol adsorption and its impact on solute retentions in supercritical fluid chromatography2016In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1442, p. 129-139Article in journal (Refereed)
    Abstract [en]

    Surface excess adsorption isotherms of methanol on a diol silica adsorbent were measured in supercritical fluid chromatography (SFC) using a mixture of methanol and carbon dioxide as mobile phase. The tracer pulse method was used with deuterium labeled methanol as solute and the tracer peaks were detected using APCI-MS over the whole composition range from neat carbon dioxide to neat methanol. The results indicate that a monolayer (4 angstrom) of methanol is formed on the stationary phase. Moreover, the importance of using the set or the actual methanol fractions and volumetric flows in SFC was investigated by measuring the mass flow respective pressure and by calculations of the actual volume fraction of methanol. The result revealed a significant difference between the value set and the actually delivered volumetric methanol flow rate, especially at low modifier fractions. If relying only on the set methanol fraction in the calculations, the Methanol layer thickness should in this system be highly overestimated. Finally, retention times for a set of solutes were measured and related to the findings summarized above concerning methanol adsorption. A strongly non-linear relationship between the logarithms of the retention factors and the modifier fraction in the mobile phase was revealed, prior to the established monolayer. At modifier fractions above that required for establishment of the methanol monolayer, this relationship turns linear which explains why the solute retention factors are less sensitive to changes in modifier content in this region.

  • 61.
    Hernandez, Victor Agmo
    et al.
    Uppsala University, Sweden.
    Samuelsson, Jorgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Forssen, 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. Uppsala University, Sweden.
    Enhanced interpretation of adsorption data generated by liquid chromatography and by modern biosensors2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1317, p. 22-31Article in journal (Refereed)
    Abstract [en]

    In this study we demonstrate the importance of proper data processing in adsorption isotherm estimations. This was done by investigating and reprocessing data from five cases on two closely related platforms: liquid chromatography (LC) and biosensors. The previously acquired adsorption data were reevaluated and reprocessed using a three-step numerical procedure: (i) preprocessing of adsorption data, (ii) adsorption data analysis and (iii) final rival model fit. For each case, we will discuss what we really measure and what additional information can be obtained by numerical processing of the data. These cases clearly demonstrate that numerical processing of LC and biosensor data can be used to gain deeper understanding of molecular interactions with adsorption media. This is important because adsorption data, especially from biosensors, is often processed using old and simplified methods. (C) 2013 Elsevier B.V. All rights reserved.

  • 62.
    Lesko, Marek
    et al.
    Rzeszów University of Technology, Poland.
    Åsberg, Dennis
    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).
    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).
    Kaczmarski, Krzysztof
    Poland.
    Choice of Model for Estimation of Adsorption Isotherm Parameters in Gradient Elution Preparative Liquid Chromatography2015In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 78, no 19-20, p. 1293-1297Article in journal (Refereed)
    Abstract [en]

    The inverse method is a numerical method for fast estimation of adsorption isotherm parameters directly from a few overloaded elution profiles and it was recently extended to adsorption isotherm acquisition in gradient elution conditions. However, the inverse method in gradient elution is cumbersome due to the complex adsorption isotherm models found in gradient elution. In this case, physicochemically correct adsorption models have very long calculation times. The aim of this study is to investigate the possibility of using a less complex adsorption isotherm model, with fewer adjustable parameters, but with preserved/acceptable predictive abilities. We found that equal or better agreement between experimental and predicted elution profiles could be achieved with less complex models. By being able to select a model with fewer adjustable parameters, the calculation times can be reduced by at least a factor of 10. 

  • 63.
    Liangsupree, Thanaporn
    et al.
    University Helsinki, Finland.
    Multia, Evgen
    University Helsinki, Finland.
    Metso, Jari
    Biomedicum 2U, Finland.
    Jauhiainen, Matti
    Biomedicum 2U, Finland.
    Forssén, Patrik
    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).
    Oorni, Katariina
    Wihuri Research Institute, Finland.
    Podgornik, Ales
    University Ljubljana, Slovenia.
    Riekkola, Marja-Liisa
    University Helsinki, Finland.
    Rapid affinity chromatographic isolation method for LDL in human plasma by immobilized chondroitin-6-sulfate and anti-apoB-100 antibody monolithic disks in tandem2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 11235Article in journal (Refereed)
    Abstract [en]

    Low-density lipoprotein (LDL) is considered the major risk factor for the development of atherosclerotic cardiovascular diseases (ASCVDs). A novel and rapid method for the isolation of LDL from human plasma was developed utilising affinity chromatography with monolithic stationary supports. The isolation method consisted of two polymeric monolithic disk columns, one immobilized with chondroitin-6-sulfate (C6S) and the other with apolipoprotein B-100 monoclonal antibody (anti-apoB-100 mAb). The first disk with C6S was targeted to remove chylomicrons, very-low-density lipoprotein (VLDL) particles, and their remnants including intermediate-density lipoprotein (IDL) particles, thus allowing the remaining major lipoprotein species, i.e. LDL, lipoprotein(a) (Lp(a)), and high-density lipoprotein (HDL) to flow to the anti-apoB-100 disk. The second disk captured LDL particles via the anti-apoB-100 mAb attached on the disk surface in a highly specific manner, permitting the selective LDL isolation. The success of LDL isolation was confirmed by different techniques including quartz crystal microbalance. In addition, the method developed gave comparable results with ultracentrifugation, conventionally used as a standard method. The reliable results achieved together with a short isolation time (less than 30 min) suggest the method to be suitable for clinically relevant LDL functional assays.

  • 64.
    Lin, G.
    et al.
    Zhejiang Univ, China.
    Zhang, Y.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Örebro universitet.
    Cheng, X.
    Zhejiang Univ, China.
    Gulliksson, M.
    Örebro universitet.
    Forssén, Patrik
    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 regularizing Kohn-Vogelius formulation for the model-free adsorption isotherm estimation problem in chromatography2018In: Applicable Analysis, ISSN 0003-6811, E-ISSN 1563-504X, Vol. 97, no 1, p. 13-40Article in journal (Refereed)
    Abstract [en]

    Competitive adsorption isotherms must be estimated in order to simulate and optimize modern continuous modes of chromatography in situations where experimental trial-and-error approaches are too complex and expensive. The inverse method is a numeric approach for the fast estimation of adsorption isotherms directly from overloaded elution profiles. However, this identification process is usually ill-posed. Moreover, traditional model-based inverse methods are restricted by the need to choose an appropriate adsorption isotherm model prior to estimate, which might be very hard for complicated adsorption behavior. In this study, we develop a Kohn-Vogelius formulation for the model-free adsorption isotherm estimation problem. The solvability and convergence for the proposed inverse method are studied. In particular, using a problem-adapted adjoint, we obtain a convergence rate under substantially weaker and more realistic conditions than are required by the general theory. Based on the adjoint technique, a numerical algorithm for solving the proposed optimization problem is developed. Numerical tests for both synthetic and real-world problems are given to show the efficiency of the proposed regularization method.

  • 65.
    Lipponen, Katriina
    et al.
    Univ Helsinki, Dept Chem, Analyt Chem Lab, FIN-00014 Helsinki, Finland..
    Stege, Patricia W.
    Univ Helsinki, Dept Chem, Analyt Chem Lab, FIN-00014 Helsinki, Finland.;Natl Univ San Luis, CONICET, Dept Chem, INQUISAL,Lab Analyt Chem, San Luis, Argentina..
    Cilpa, Geraldine
    Univ Helsinki, Dept Chem, Analyt Chem Lab, FIN-00014 Helsinki, Finland..
    Samuelsson, Jorgen
    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. Karlstad Univ, Dept Chem & Biomed Sci, SE-65188 Karlstad, Sweden.;Uppsala Univ, Dept Phys & Analyt Chem, SE-75124 Uppsala, Sweden..
    Riekkola, Marja-Liisa
    Univ Helsinki, Dept Chem, Analyt Chem Lab, FIN-00014 Helsinki, Finland..
    Three Different Approaches for the Clarification of the Interactions between Lipoproteins and Chondroitin-6-sulfate2011In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 83, no 15, p. 6040-6046Article in journal (Refereed)
    Abstract [en]

    Two different experimental approaches were used for obtaining a comprehensive view and understanding of the interactions between apolipoprotein B-100 (ApoB-100) of low-density lipoprotein and apolipoprotein E (ApoE) of high-density lipoprotein and chondroitin-6-sulfate (C6S) of arterial proteoglycan. The techniques employed were partial filling affinity capillary electrophoresis (PF-ACE) and continuous flow quartz crystal inicrobalance (QCM). In addition, molecular dynamic (MD) simulations were used to provide a supportive visual insight into the interaction mechanism. A new tool for analysis of QCM-data was utilized, i.e., adsorption energy distribution calculations, which allowed a deeper understanding of the interactions, especially at different temperatures. The PF-ACE technique probed mainly the strong adsorption interactions whereas in the MD calculations short:- and long-range interactions could be distinguished. Although there are differences in the techniques, a pretty good agreement was achieved between the three approaches for the interaction of 19 amino acid peptide of ApoB with C6S giving log affinity constants of 4.66 by QCM, 5.02 by PP-ACE, and 7.39 by MD, and for 15 amino acid peptide of ApoE with C6S 5.34 by QCM, 5.28 by PT-ACE, and 4.60 by MD at physiological temperature 37.0 degrees C.

  • 66.
    Lipponen, Katriina
    et al.
    Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Helsinki, Finland.
    Tähkä, Sari
    Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Helsinki, Finland.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Jauhiainen, Matti
    National Institute for Health and Welfare and FIMM, Institute of Molecular Medicine Finland, Biomedicum, Haartmaninkatu 8, FIN-00290 Helsinki,.
    Metso, Jari
    National Institute for Health and Welfare and FIMM, Institute of Molecular Medicine Finland, Biomedicum, Haartmaninkatu 8, FIN-00290 Helsinki, Finland,.
    Cilpa-Karhu, Geraldine
    Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Helsinki, Finland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Kostiainen, Mauri
    Biohybrid Materials, Department of Biotechnology and Chemical Technology, FIN-00076 Aalto University, Espoo, Finland.
    Riekkola, Marja-Liisa
    Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Helsinki, Finland.
    Partial-filling affinity capillary electrophoresis and quartz crystal microbalance with adsorption energy distribution calculations in the study of biomolecular interactions with apolipoprotein E as interaction partner2014In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 406, no 17, p. 4137-4146Article in journal (Refereed)
    Abstract [en]

    Adsorption energy distribution (AED) calculations were successfully applied to partial-filling affinity capillary electrophoresis (PF-ACE) to facilitate more detailed studies of biomolecular interactions. PF-ACE with AED calculations was employed to study the interactions between two isoforms of apolipoprotein E (apoE) and dermatan sulfate (DS), and a quartz crystal microbalance (QCM) was used in combination with AED calculations to examine the interactions of the 15-amino-acid peptide fragment of apoE with DS. The heterogeneity of the interactions was elucidated. Microscale thermophoresis was used to validate the results. The interactions studied are of interest because, in vivo, apolipoprotein E localizes on DS-containing regions in the extracellular matrix of human vascular subendothelium. Two-site binding was demonstrated for the isoform apoE3 and DS, but only one-site binding for apoE2–DS. Comparable affinity constants were obtained for the apoE2–DS, apoE3–D3, and 15-amino-acid peptide of apoE–DS using the three techniques. The results show that combining AED calculations with modern biosensing techniques can open up another dimension in studies on the heterogeneity and affinity constants of biological molecules.

  • 67.
    Multia, Evgen
    et al.
    University of Helsinki, Finland..
    Sirén, Heli
    Uppsala universitet.
    Andersson, Karl
    Uppsala universitet.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Forssén, Patrik
    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).
    Öörni, Katariina
    Wihuri Research Institute Finland.
    Jauhiainen, Matti
    National Institute for Health and Welfare Finland.
    Riekkola, Marja-Liisa
    University of Helsinki, Finland.
    Thermodynamic and kinetic approaches for evaluation of monoclonal antibody - Lipoprotein interactions.2016In: Analytical Biochemistry, ISSN 0003-2697, E-ISSN 1096-0309, Vol. 518, p. 25-34Article in journal (Refereed)
    Abstract [en]

    Two complementary instrumental techniques were used, and the data generated was processed with advanced numerical tools to investigate the interactions between anti-human apoB-100 monoclonal antibody (anti-apoB-100 Mab) and apoB-100 containing lipoproteins. Partial Filling Affinity Capillary Electrophoresis (PF-ACE) combined with Adsorption Energy Distribution (AED) calculations provided information on the heterogeneity of the interactions without any a priori model assumptions. The AED calculations evidenced a homogenous binding site distribution for the interactions. Quartz Crystal Microbalance (QCM) studies were used to evaluate thermodynamics and kinetics of the Low-Density Lipoprotein (LDL) and anti-apoB-100 Mab interactions. High affinity and selectivity were observed, and the emerging data sets were analysed with so called Interaction Maps. In thermodynamic studies, the interaction between LDL and anti-apoB-100 Mab was found to be predominantly enthalpy driven. Both techniques were also used to study antibody interactions with Intermediate-Density (IDL) and Very Low-Density (VLDL) Lipoproteins. By screening affinity constants for IDL-VLDL sample in a single injection we were able to distinguish affinity constants for both subpopulations using the numerical Interaction Map tool.

  • 68.
    Petersson, Patrik
    et al.
    AstraZeneca R&D Lund, SE-221 87 Lund, Sweden.
    Forssén, Patrik
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Edström, Lena
    Department of Physical and Analytical Chemistry, BMC Box 577, SE-751 23 Uppsala, Sweden.
    Samie, Farzad
    AstraZeneca Nordic Headquarters (ISMO), Södertälje.
    Tatterton, Stephen
    AstraZeneca R&D Charnwood, Loughborough, Leicestershire LE11 5RH, UK.
    Clarke, Adrian
    AstraZeneca R&D Charnwood, Loughborough, Leicestershire LE11 5RH, UK.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Why ultra high performance liquid chromatography produces more tailing peaks than high performance liquid chromatography, why it does not matter and how it can be addressed2011In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 1218, no 39, p. 6914-6921Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to demonstrate, with experiments and with computer simulations based on a firm chromatographic theory, that the wide spread perception of that the United States Pharmacopeia tailing factor must be lower than 2 (Tf < 2) is questionable when using the latest generation of LC equipment. It is shown that highly efficient LC separations like those obtained with sub-2 μm porous and 2.7 μm superficially porous particles (UHPLC) produce significantly higher Tf-values than the corresponding separation based on 3 μm porous particles (HPLC) when the same amount of sample is injected. Still UHPLC separations provide a better resolution to adjacent peaks. Expressions have been derived that describe how the Tf-value changes with particle size or number of theoretical plates. Expressions have also been derived that can be used to scale the injection volume based on particle size or number of theoretical plates to maintain the Tf-value when translating a HPLC separation to the corresponding UHPLC separation. An aspect that has been ignored in previous publications. Finally, data obtained from columns with different age/condition indicate that Tf-values should be complemented by a peak width measure to provide a more objective quality measure.

  • 69.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Cavazzini, Alberto
    Univ Ferrara, Dept Chem & Pharmaceut Sci, I-44100 Ferrara, Italy..
    Shalliker, Ross Andrew
    Uppsala Univ, Dept Chem BMC, Uppsala, Sweden.;Univ Western Sydney, Australian Ctr Res Separat Sci ACROSS, Sch Sci & Hlth, Parramatta, NSW, Australia..
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Regeneration of a silica monolithic rod column using harsh methods followed by firm thermodynamic and kinetic validation2014In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 37, no 8, p. 906-911Article in journal (Refereed)
    Abstract [en]

    In this study, a numerical tool is introducedbased on thermodynamic and kinetic separation theoryfor validating the regeneration of monolithic rod columns after cutting their inlet sections. A long-used RP-18e monolithic column was deemed to be unfit for further coffee analysis because of poor separation performance. The columns brownish inlet section was physically removed with a lathe, leaving a clean white inlet section. The original and regenerated columns were extensively analyzed and compared using numerical tools for processing adsorption data. The perturbation peak method was used to measure the adsorption isotherm of phenol on the original and regenerated monolith and the adsorption energy distributions were calculated for identifying any change in the degree of heterogeneity. Although peak shapes improved considerably after regeneration, no significant differences were found in the detailed characterization of the processed adsorption data between the original column and the regenerated one. This indicates that the removal of a section of the monolithic bed can be undertaken without damaging the column and columns in which their inlet head sections are contaminated may still function with normal adsorption behavior. In addition, the combined thermodynamic and kinetic methodology could accurately be used to evaluate any regeneration method of columns.

  • 70.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Eiriksson, F. F.
    University of Iceland.
    Åsberg, Dennis
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Thorsteinsdóttir, M.
    University of Iceland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Determining gradient conditions for peptide purification in RPLC with machine-learning-based retention time predictions2019In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1598, p. 92-100Article in journal (Refereed)
    Abstract [en]

    A strategy for determining a suitable solvent gradient in silico in preparative peptide separations is presented. The strategy utilizes a machine-learning–based method, called ELUDE, for peptide retention time predictions based on the amino acid sequences of the peptides. A suitable gradient is calculated according to linear solvent strength theory by predicting the retention times of the peptides being purified at three different gradient slopes. The advantage of this strategy is that fewer experiments are needed to develop a purification method, making it useful for labs conducting many separations but with limited resources for method development. The preparative separation of met-enkephalin and leu-enkephalin was used as model solutes on two stationary phases: XBridge C18 and CSH C18. The ELUDE algorithm contains a support vector regression and is pre-trained, meaning that only 10–50 peptides are needed to calibrate a model for a certain stationary phase and gradient. The calibration is done once and the model can then be used for new peptides similar in size to those in the calibration set. We found that the accuracy of the retention time predictions is good enough to usefully estimate a suitable gradient and that it was possible to compare the selectivity on different stationary phases in silico. The absolute relative errors in retention time for the predicted gradients were 4.2% and 3.7% for met-enkephalin and leu-enkephalin, respectively, on the XBridge C18 column and 2.0% and 2.8% on the CSH C18 column. The predicted retention times were also used as initial values for adsorption isotherm parameter determination, facilitating the numerical calculation of overloaded elution profiles. Changing the trifluoroacetic acid (TFA) concentration from 0.05% to 0.15% in the eluent did not seriously affect the error in the retention time predictions for the XBridge C18 column, an increase of 1.0 min (in retention factor, 1.3). For the CSH C18 column the error was, on average, 2.6 times larger. This indicates that the model needs to be recalibrated when changing the TFA concentration for the CSH column. Studying possible scale-up complications from UHPLC to HPLC such as pressure, viscous heating (i.e., temperature gradients), and stationary-phase properties (e.g., packing heterogeneity and surface chemistry) revealed that all these factors were minor to negligible. The pressure effect had the largest effect on the retention, but increased retention by only 3%. In the presented case, method development can therefore proceed using UHPLC and then be robustly transferred to HPLC.

  • 71.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enmark, Martin
    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.
    Highlighting Important Parameters Often Neglected in Numerical Optimization of Preparative Chromatography2012In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 35, no 1, p. 149-156Article in journal (Refereed)
    Abstract [en]

    When a chromatographic separation process is numerically optimized, a number of input parameters to the column model need to be accurately determined, and the accuracy will affect the reliability of the predicted optimal operational conditions. Furthermore, the numerical accuracy of the solution to the column model will have similar impact. The input parameters holdup volume, injection profiles, and the selection of an algorithm for solving the column model were investigated. Errors in parameters or a numerical error in the solution of the column model were found to lead to a prediction of a product fraction where the set purity and/or yield requirements are not met.

  • 72.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enmark, Martin
    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.
    Characterization of adsorption in SFC: An evaluation of methods used in LC2012Conference 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

  • 73.
    Samuelsson, Jörgen
    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.
    Recent Developments on the Elution by Characteristic Points Method for Rapid and Accurate Determination of Adsorption Isotherms2011Other (Other academic)
    Abstract [en]

    Adsorption isotherms are the most important pieces of information needed to understand the analytical and preparative separation system. Several methods are used for their determinations. In this poster we will analyze the elution by characteristic point method (ECP) that is faster and also consumes less amounts analyte and solvent as compared to classic methods such as the frontal analysis (FA) and the perturbation peak method. Classically, ECP is conducted by integrating the diffuse part of an overloaded elution profile, which means that just one single overloaded elution profile and a calibration curve is needed to determine the adsorption isotherm. However, the ECP method is derived assuming that the column has infinite efficiency and that the injection profile is rectangular. All deviation from this will lead to errors in the determined adsorption isotherm. Because the adsorption isotherm is also integrated, a continuous diffuse part of the elution profiles is required. This means that adsorption isotherms from only tailing and fronting peaks could classically only be determined. In this poster we will present: (i) A method to experimentally achieve rectangular injection-profiles [1]. (ii) Determination of the raw slope of the adsorption isotherm data without integrating the elution profile. (iii) Strategies to expand the ECP method for the determination of more complex adsorption isotherms including such containing inflection points [3]. [1] J. Samuelsson, T. Fornstedt, Anal. Chem. 80 (2008) 7887. [2] J. Samuelsson, T. Undin, A. Törncrona, T. Fornstedt, J. Chromatogr. A 1217 (2010) 7215. [3]. J. Samuelsson, T. Undin, T. Fornstedt, J. Chromatogr. A, under review

  • 74.
    Samuelsson, Jörgen
    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.
    Högblom, Joakim
    Eka Chemicals.
    A Holistic View on Optimization of Preparative Liquid Chromatography – Importance of Column Properties and Design.2012Conference paper (Refereed)
    Abstract [en]

    Several important studies based on firm theory ground - have been made on the different parameters of importance in chromatographic process optimizations during the recent years. In this presentation we take an holistic view by investigating i) the relative importance of the operational parameters and column properties and ii) how these effect the optimal column design. For optimization we used an advanced global response surface method combined with local gradient methods. As a model system we used the practical problem of purification of one or both optical isomers of a racemate. In the first part, we investigated the relative importance of stationary phase characteristics such as: (i) the retention factor, (ii) the selectivity, (iii) the saturation capacity (iv), the efficiency and (v) the maximum allowed operational pressure. In the second part we investigated how the optimal column design for a preparative separation problem is affected by column properties, such as particle size, and optimization constraints, such as required yield. The investigation showed – in contrast to what is generally believed – that the saturation capacity of the stationary phase is of minor importance, instead the maximum allowed operational pressure is one of the most important parameter. Moreover, smaller size packing materials always shows much lower solvent consumption. This is a great environmental and economical advantage of using smaller packing materials. Rules of thumbs, derived from the holistic optimizations, will be given for industrial preparative settings in the batch mode.

  • 75.
    Samuelsson, Jörgen
    et al.
    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, Andrew
    Australia.
    Exogenous factors contributing to column bed heterogeneity: Part 1: Consequences of 'air' injections in liquid chromatography2015In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1406, p. 186-91Article in journal (Refereed)
    Abstract [en]

    It has been shown that not only the packing homogeneity, but also factors external to the column bed, such as, frits and distributors can have important effects on the column performance. This current communication is the first in a series focusing on the impact of exogenous factors on the column bed heterogeneity. This study is based on several observations by us and others that chromatographic runs often, for technical reasons, include more or less portions of air in the injections. It is therefore extremely important to find out the impact of air on the column performance, the reliability of the results derived from analyses where air was injected, and the effect on the column homogeneity. We used a photographic approach for visualising the air transport phenomena, and found that the air transport through the column is comprised of many different types of transport phenomena, such as laminal flow, viscous fingering like flows, channels and bulbs, and pulsations. More particularly, the air clouds within the column definitely interact in the adsorption, i.e. mobile phase adsorbed to the column surface is displaced. In addition, irrespective of the type of air transport phenomena, the air does not penetrate the column homogeneously. This process is strongly flow dependent. In this work we study air transport both in an analytical scale and a semi-prep column.

  • 76.
    Samuelsson, Jörgen
    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.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Sample conditions to avoid pH distortion in RP-LC2013In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 36, no 23, p. 3769-3775Article in journal (Refereed)
    Abstract [en]

    Band deformations might take place for acids and bases in preparative applications and adsorption studies where it is necessary to use overloaded injections. In this study, we focus on how deformations can be prevented without using highly concentrated buffers that may precipitate in the eluent. We have systematically investigated how the elution zones depend on which protolytic form the analyte has when it is dissolved. Basic and acidic model compounds are investigated using eluents with different pH values and the resulting elution profiles are compared when the analytes are dissolved in their protonated and deprotonated form, i.e., in uncharged form or as different kinds of salts. Depending on the analyte's protolytic form, a sample zone is created at the column inlet whose pH deviates, more or less, from the bulk eluent's. If the local adsorption strength in this sample zone is greater than the bulk eluent's, the elution profiles are compressed. Under opposite conditions, the eluted bands are more or less deformed and may even be split; completely different deformations can even take place for different kinds of salt combinations. Explanations of these, and other, effects, together with detailed guidelines for proper sample preparation to avoid peak deformations, are given.

  • 77.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Shalliker, R. Andrew
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci, North Parramatta, NSW 2751, Australia..
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Viscosity contrast effects in analytical scale chromatography: Evidence and impact2017In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 130, p. 102-107Article in journal (Refereed)
    Abstract [en]

    The phenomenon known as viscous fingering has been shown to be very detrimental to separation performance in preparative and size exclusion chromatography, and also in multidimensional HPLC However, there are few reports of viscous fingering in analytical scale high performance liquid chromatography (HPLC), despite samples very often being introduced to the analytical-size HPLC columns in a solvent have a substantially different viscosity than the mobile phase. With this study we aim at first hand to investigate if viscous fingering or any similar and related effects to these in preparative levels also take place in analytical scale HPLC and if so, what impact this have on the separation performance. We could show that not only viscous finger does occur in analytical scale columns but also that peak distortions are apparent already at viscosity ratios between eluent and sample solution approaching unity. The latter indicates that a pre-viscous phenomenon is occurring that could be more important than the viscous fingering itself at the analytical format. As the viscosity contrast increases, the leading edge of the sample band distorts and the band volume increases, both leading to a decrease in performance.

  • 78.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Undin, Torgny
    Uppsala University.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Expanding the elution by characteristic point method for determination of various types of adsorption isotherms2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 24, p. 3737-3742Article in journal (Refereed)
    Abstract [en]

    Important improvements have recently been made on the elution by characteristic point (ECP) method to increase the accuracy of the determined adsorption isotherms. However, the method has so far been limited/used for only type I adsorption isotherms (e.g. Langmuir, Tóth, bi-Langmuir). In this study, general strategies are developed to expand the ECP method for the determination of more complex adsorption isotherms including such containing inflection points. We will exemplify the methodology with type II, type III and type V isotherms. Guidelines are given for how to determine such isotherms using the ECP method and for the experimental considerations that must be taken into account or that may be eliminated in the particular case.

  • 79.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Undin, Torgny
    Uppsala University, Sweden.
    Törncrona, Anders
    Eka Chemicals AB, Sweden.
    Fornstedt, Torgny
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Improvement in the generation of adsorption isotherm data in the elution by characteristic points method-: the ECP-slope approach2010In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1217, no 46, p. 7215-7221Article in journal (Refereed)
    Abstract [en]

    The elution by characteristic points (ECP) method is a very rapid and precise method for determination of the phase system equilibrium of phase systems in broad solute concentration ranges. Thus, the method is especially suitable for rapid characterization of high efficient separation systems. One important source of error, the effects by the post-loop dispersion, was eliminated in a recent investigation. In this study, the systematic error caused by the selection of the integration starting point at concentration equal to 0 is eliminated. This is done by developing and validating a new procedure for isotherm data generation; the ECP-slope method. The method generates raw slope data of the adsorption isotherm instead of raw adsorption data by integrations as the classical ECP does. Both numerical and experimental data were used for the comparison of the classical ECP approach with the slope-ECP method

  • 80.
    Samuelsson, Jörgen
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Ņsberg, Dennis
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enmark, Martin
    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.
    Modeling Competitive Adsorption Isotherms in Gradient Elution Nonlinear Reversed Phase Liquid Chromatography.2012Conference paper (Refereed)
    Abstract [en]

    Several important studies – based on firm theory ground - have been made on the different parameters of importance in chromatographic process optimizations during the recent years. In this presentation we take an holistic view by investigating i) the relative importance of the operational parameters and column properties and ii) how these effect the optimal column design. For optimization we used an advanced global response surface method combined with local gradient methods. As a model system we used the practical problem of purification of one or both optical isomers of a racemate. In the first part, we investigated the relative importance of stationary phase characteristics such as: (i) the retention factor, (ii) the selectivity, (iii) the saturation capacity (iv), the efficiency and (v) the maximum allowed operational pressure. In the second part we investigated how the optimal column design for a preparative separation problem is affected by column properties, such as particle size, and optimization constraints, such as required yield. The investigation showed – in contrast to what is generally believed – that the saturation capacity of the stationary phase is of minor importance, instead the maximum allowed operational pressure is one of the most important parameter. Moreover, smaller size packing materials always shows much lower solvent consumption. This is a great environmental and economical advantage of using smaller packing materials. Rules of thumbs, derived from the holistic optimizations, will be given for industrial preparative settings in the batch mode.

  • 81.
    Sandblad, Peter
    et al.
    Uppsala universitet, Institutionen för fysikalisk och analytisk kemi.
    Arnell, Robert
    Uppsala universitet, Institutionen för fysikalisk och analytisk kemi.
    Samuelsson, Jörgen
    UDepartment of Physical and Analytical Chemistry, BMC Box 599, SE-751 24, Uppsala, Sweden.
    Fornstedt, Torgny
    Department of Physical and Analytical Chemistry, BMC Box 599, SE-751 24, Uppsala, Sweden.
    Approach for reliable evaluation of drug proteins interactions using surface plasmon resonance technology2009In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 9, p. 3551-3559Article in journal (Refereed)
    Abstract [en]

    The surface plasmon resonance (SPR) biosensor was recently introduced to the analytical biochemical society for measuring small drug-protein interactions. However, the technique has many times been used without specifying the type of enantiomeric form of the chiral drug measured and/or with using a too narrow drug concentration range resulting in biased values of binding coefficients and sometimes even assumptions about single-site bindings although the binding in reality comprises a multisite interaction. In this study we will give guidelines for reliable experimental and methodological approaches to avoid these pitfalls. For this purpose, we also introduce a new tool, based on physical chemistry, to the sensor community; the calculation of the adsorption energy distribution (AED). The AED-calculations reveal the degree of heterogeneity directly from the SPR raw data and thus guide us into a narrower selection of probable models before the rival model fitting procedure. We demonstrate how to measure reliable equilibrium data for the two typically different cases: drug binding to (i) transport (plasma) proteins and to (ii) a target protein. Both the binding of the chiral beta-blocker propranolol to alpha(1)-acid glycoprotein (AGP) and that of the anticoagulant warfarin to human serum albumin were heterogeneous, with a few strong enantioselective sites and many weak nonselective sites. We also demonstrate how the multisite binding rapidly falsely turns to single-site as the concentration range is narrowed and how adding dimethyl sulfoxide to the buffer affects multisite drug-protein data. The binding of the enantiomers of the thrombin inhibitor melagatran was investigated on both thrombin and the transport proteins, revealing clear enantioselectivity for thrombin in favor of the active enantiomer, but almost similar binding properties for both enantiomers to the transport protein AGP. The AED-calculations verified that both these system has a unimodal energy distribution and are best described with a homogeneous adsorption model.

  • 82.
    Shalliker, R. Andrew
    et al.
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci ACROSS, North Parramatta, NSW 2150, Australia.;Karlstad Univ, INTERACT, Dept Engn & Chem Sci, SE-65188 Karlstad, Sweden..
    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).
    Sample introduction for high performance separations2016In: TrAC. Trends in analytical chemistry, ISSN 0165-9936, E-ISSN 1879-3142, Vol. 81, p. 34-41Article, review/survey (Refereed)
    Abstract [en]

    In this review we discuss how viscosity contrasts between the injection plug and the mobile phase may lead to loss in separation performance, especially in UHPLC columns or SFC environments. Firstly, the wall effect is discussed, and how it can amplify viscosity contrast effects. We then illustrate how viscosity contrasts lead to the phenomenon known as viscous fingering, and we detail the destructive effects of this phenomenon. We expand on the viscous fingering component, however, demonstrating that viscosity contrast effects begin to deteriorate performance long before the conditions are such that viscous fingering occurs. Subtle changes in band-shape are apparent even with very low viscosity contrasts. Lastly we illustrate how viscosity contrast effects lead to severe peak distortions in SFC. Analysts who seek high efficiency separations must make every effort to eliminate, or at least minimise the viscosity contrast between the injection plug and the mobile phase. 

  • 83.
    Undin, Torgny
    et al.
    Department of Chemistry –BMC, Uppsala University,Uppsala, Sweden.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. Department of Chemistry –BMC, Uppsala University,Uppsala, Sweden.
    Törncrona, Anders
    AkzoNobel Pulp & Performance Chemicals AB, Bohus, Sweden.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Evaluation of a combined linear–nonlinear approach for column characterization using modern alkaline-stable columns as model2013In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 36, no 11, p. 1753-1761Article in journal (Refereed)
    Abstract [en]

    This study investigates if deeper understanding is achieved when combining nonlinear and linear chromatographic column characterization methods. As test systems, two hybrid columns (Phenomenex Gemini-NX C18 and Kromasil Eternity C18) and one classic one (Kromasil-C18) were selected. The nonlinear methods were based on firm adsorption theory and involved determination of adsorption isotherms followed by calculations with a new numerical tool, adsorption energy distribution, on probe components at different pH values. The linear methods involved the hydrophobic subtraction model and selected probe components retention factors as a function of pH. The combined analysis indicated that both complementary and confirmative information can be achieved regarding the actual model systems.

  • 84. Vera, C. M.
    et al.
    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).
    Dennis, G. R.
    Shalliker, R. A.
    Protocol for the visualisation of axial temperature gradients in ultra high performance liquid chromatography using infrared cameras2018In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 141, p. 141-147Article in journal (Refereed)
    Abstract [en]

    A protocol was developed for the visualisation of axial temperature gradients on a Kinetex column (1.3 μm C18 100 Å 50 × 2.1 mm) operated at near maximum pressure of the system (Pmax) using an infrared camera. Real time viscous frictional heating effects across the entire column length was observed, and showed that with increasing flow rate there was an increase in the maximum temperature of the column, and the difference between the inlet and outlet temperatures. Temperature profile data over the entire length of the column revealed the dynamics of heat exchange processes along different parts of the column, and raises the question on potential heating effects on eluents. The axial temperature gradients of eluents such as pure methanol, isopropyl alcohol and acetonitrile near Pmax were compared; finding that acetonitrile which had the highest flow velocity at Pmax gave the highest overall temperature increase for these eluents.

  • 85.
    Vera, C. M.
    et al.
    Western Sydney Univ, Australian.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences. 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). Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Dennis, G. R.
    Western Sydney Univ, Australian.
    Shalliker, R. A.
    Western Sydney Univ, Australian.
    Visualisation of axial temperature gradients and heat transfer process of different solvent compositions in ultra high performance liquid chromatography using thermography2019In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 145, p. 927-935Article in journal (Refereed)
    Abstract [en]

    Thermal imaging was used to visualise axial temperature gradients in chromatography columns running solvents of water, methanol and acetonitrile at various compositions. The non-monotonic relationship between solvent composition and viscosity enabled the testing of solvent conditions with equivalent viscosities, but with different percentages of water. It was observed that at equivalent power the increase in water composition leads to an increase in the magnitude of the axial temperature gradients (Delta T-A). Observing the change in temperature at defined points (Delta T-p) with increasing power indicates that the relationship between Delta T-p and power is not linear but deviates at higher power. The degree of this deviation depends on what point along the column axis is observed as well what solvent composition is used. Being able to monitor the entire length of the column using thermography also allowed for the observation of different rates of heat transfer through to the bulky stainless steel end fittings from solvent to solvent. Revealing that water is able to transfer heat to the stainless steel surface in such a way that the temperature profile of transition point between columns to end fitting is more gradual compared to when methanol or acetonitrile is used. This evidence plus video data collected indicates that at constant flow rate an equilibrium between heat generated and heat dissipated through the stainless steel is formed, which differs from solvent to solvent. Moreover any disruption to this equilibrium, i.e. a change in flow rate will momentarily change the shape of the temperature profile.

  • 86.
    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.
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci, Penrith, NSW 2751, Australia..
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Enmark, Martin
    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.
    Shalliker, R. A.
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci, Penrith, NSW 2751, Australia.
    Contrasting selectivity between HPLC and SFC using phenyl-type stationary phases: A study on linear polynuclear aromatic hydrocarbons2015In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 119, p. 40-43Article in journal (Refereed)
    Abstract [en]

    A selectivity study was undertaken using two types of phenyl-type (Synergi polar RP and Cosmosil 5PBB) stationary phases in supercritical fluid chromatography. The mobile phases used in the SFC environment employed CO2 with methanol as the modifier. These columns were tested using linear polynuclear aromatic hydrocarbons as the test solutes. The retention behaviour of these PAHs in SFC was compared to their behaviour in HPLC and there were very distinct differences. On the Synergi-polar stationary phase the PAH selectivity was highly dependent on the methanol modifier concentration, but in comparison on the Cosmosil column, the selectivity between the members of this PAH test group showed almost no change as a function of the methanol concentration, even though the retentivity on the Cosmosil stationary phase was far greater than the Synergi stationary. In fact, the mobile phase played a very passive role in the separations observed on the Cosmosil stationary phase. (C) 2014 Elsevier B.V. All rights reserved.

  • 87.
    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.
    Enmark, Martin
    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.
    Shalliker, R. Andrew
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. 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.

  • 88.
    Zhang, Xiaoou
    et al.
    Department of Biological Science and Technology, School of Environmental and Biological Science and Technology, Dalian University of Technology, Dalian, 116024, China.
    Samuelsson, Jörgen
    Uppsala universitet, Institutionen för fysikalisk och analytisk kemi.
    Janson, Jan-Christer
    Uppsala universitet, Institutionen för fysikalisk och analytisk kemi.
    Wang, Changhai
    Department of Biological Science and Technology, School of Environmental and Biological Science and Technology, Dalian University of Technology, Dalian, 116024, China..
    Su, Zhiguo
    National Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Box 353, Beijing, 100190, China.
    Gu, Ming
    National Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Box 353, Beijing, 100190, China.
    Fornstedt, Torgny
    Uppsala universitet, Institutionen för fysikalisk och analytisk kemi.
    Investigation of the adsorption behavior of glycine peptides on 12% cross-linked agarose gel media2010In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1217, no 12, p. 1916-1925Article in journal (Refereed)
    Abstract [en]

    The highly cross-linked 12% agarose gel Superose 12 10/300 GL Causes retardation of glycine peptides when mobile phases containing varying concentrations of acetonitrile in water are used An investigation has been made into the retention mechanism behind this retardation using the glycine dipeptide (GG) and tripeptide (GGG) as models The dependence of retention times of analytical-size peaks Under different experimental conditions was interpreted such that the adsorption most probably was caused by the formation of hydrogen bonds but that electrostatic interactions cannot be ruled Out Thereafter, a nonlinear adsorption study Was undertaken at different acetonitrile content in the eluent, using the elution by characteristic points (ECPs) method on strongly overloaded GG and GGG peaks With a new evaluation tool, the adsorption energy distribution (AED) Could be calculated prior to the model selection These calculations revealed that when the acetonitrile content in the eluent was varied from 0% to 20% the interactions turned from (i) being homogenous (GG) or mildly heterogeneous (GGG), (ii) via a more or less stronger degree of heterogeneity around one site to (iii) finally a typical bimodal energy interaction comprising of two sites (GG at 20% and GGG at 10% and 20%) The Langmuir, Toth and bi-Langmuir models described these interesting adsorption trends excellently Thus, the retardation observed for these glycine peptides is interpreted as being of mixed-mode character composed of electrostatic bonds and hydrogen bonds.

  • 89.
    Zhang, Y.
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Forssén, Patrik
    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).
    Gulliksson, M.
    Orebrov Univ, Sch Sci & Technol, Dept Math, Orebro, Sweden.
    Dai, X.
    Zhejiang Univ, City Coll, Sch Comp Sci, Hangzhou, Zhejiang, Peoples R China.
    An adaptive regularization algorithm for recovering the rate constant distribution from biosensor data2018In: Inverse Problems in Science and Engineering, ISSN 1741-5977, E-ISSN 1741-5985, Vol. 26, no 10, p. 1464-1489Article in journal (Refereed)
    Abstract [en]

    We present here the theoretical results and numerical analysis of a regularization method for the inverse problem of determining the rate constant distribution from biosensor data. The rate constant distribution method is a modern technique to study binding equilibrium and kinetics for chemical reactions. Finding a rate constant distribution from biosensor data can be described as a multidimensional Fredholm integral equation of the first kind, which is a typical ill-posed problem in the sense of J. Hadamard. By combining regularization theory and the goal-oriented adaptive discretization technique, we develop an Adaptive Interaction Distribution Algorithm (AIDA) for the reconstruction of rate constant distributions. The mesh refinement criteria are proposed based on the a posteriori error estimation of the finite element approximation. The stability of the obtained approximate solution with respect to data noise is proven. Finally, numerical tests for both synthetic and real data are given to show the robustness of the AIDA.

  • 90.
    Zhang, Ye
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Orebro Univ, Sch Sci & Technol, Dept Math, Orebro, Sweden.
    Lin, G.
    Zhejiang Univ, Dept Math, Hangzhou, Zhejiang, Peoples R China..
    Gulliksson, M.
    Orebro Univ, Sch Sci & Technol, Dept Math, Orebro, Sweden..
    Forssén, Patrik
    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).
    Cheng, X.
    Zhejiang Univ, Dept Math, Hangzhou, Zhejiang, Peoples R China..
    An adjoint method in inverse problems of chromatography2017In: Inverse Problems in Science and Engineering, ISSN 1741-5977, E-ISSN 1741-5985, Vol. 25, no 8, p. 1112-1137Article in journal (Refereed)
    Abstract [en]

    How to determine adsorption isotherms is an issue of significant importance in chromatography. A modern technique of obtaining adsorption isotherms is to solve an inverse problem so that the simulated batch separation coincides with actual experimental results. In this work, as well as the natural least-square approach, we consider a Kohn-Vogelius type formulation for the reconstruction of adsorption isotherms in chromatography, which converts the original boundary fitting problem into a domain fitting problem. Moreover, using the first momentum regularizing strategy, a new regularization algorithm for both the Equilibrium-Dispersive model and the Transport-Dispersive model is developed. The mass transfer resistance coefficients in the Transport-Dispersive model are also estimated by the proposed inverse method. The computation of the gradients of objective functions for both of the two models is derived by the adjoint method. Finally, numerical simulations for both a synthetic problem and a real-world problem are given to show the robustness of the proposed algorithm.

  • 91.
    Zhang, Ye
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Örebro Universitet Sverige.
    Lin, Guang-Liang
    Zhejiang Univ, Dept Math, Hangzhou 310027, Zhejiang, Peoples R China..
    Forssén, Patrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Gulliksson, Marten
    Örebro Universitet, Sweden..
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Cheng, Xiao-Liang
    Zhejiang Univ, Dept Math, Hangzhou 310027, Zhejiang, Peoples R China..
    A regularization method for the reconstruction of adsorption isotherms in liquid chromatography2016In: Inverse Problems, ISSN 0266-5611, E-ISSN 1361-6420, Vol. 32, no 10, article id 105005Article in journal (Refereed)
    Abstract [en]

    Determining competitive adsorption isotherms is an open problem in liquid chromatography. Since traditional experimental trial-and-error approaches are too complex and expensive, a modern technique of obtaining adsorption isotherms is to solve the inverse problem so that the simulated batch separation coincides with actual experimental results. This is a typical ill-posed problem. Moreover, in almost all cases the observed concentration at the outlet is the total response of all components, which makes the problem more difficult. In this work, we tackle the ill-posedness with a new regularization method, which is based on the fact that the adsorption isotherms do not depend on the injection profile. The proposed method transfers the original problem to an optimization problem with a time-dependent convection-diffusion equation constraint. Iterative algorithms for solving constraint optimization problems for both the equilibrium-dispersive and the transport-dispersive models are developed. The mass transfer resistance is also estimated by the proposed inverse method. A regularization parameter selection method and the convergence property of the proposed algorithm are discussed. Finally, numerical tests for both synthetic problems and real-world problems are given to show the efficiency and feasibility of the proposed regularization method.

  • 92.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Chutkowski, Marcin
    Rzeszów University of Technology, Polen.
    Leśko, Marek
    Rzeszów University of Technology, Polen.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Kaczmarski, Krzysztof
    Rzeszów University of Technology, Polen.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    A practical approach for predicting retention time shifts due to pressure and temperature gradients in ultra-high-pressure liquid chromatography2017In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1479, p. 107-120Article in journal (Refereed)
    Abstract [en]

    Large pressure gradients are generated in ultra-high-pressure liquid chromatography (UHPLC) using sub–2 μm particles causing significant temperature gradients over the column due to viscous heating. These pressure and temperature gradients affect retention and ultimately result in important selectivity shifts. In this study, we developed an approach for predicting the retention time shifts due to these gradients. The approach is presented as a step-by-step procedure and it is based on empirical linear relationships describing how retention varies as a function of temperature and pressure and how the average column temperature increases with the flow rate. It requires only four experiments on standard equipment, is based on straightforward calculations, and is therefore easy to use in method development. The approach was rigorously validated against experimental data obtained with a quality control method for the active pharmaceutical ingredient omeprazole. The accuracy of retention time predictions was very good with relative errors always less than 1% and in many cases around 0.5% (n = 32). Selectivity shifts observed between omeprazole and the related impurities when changing the flow rate could also be accurately predicted resulting in good estimates of the resolution between critical peak pairs. The approximations which the presented approach are based on were all justified. The retention factor as a function of pressure and temperature was studied in an experimental design while the temperature distribution in the column was obtained by solving the fundamental heat and mass balance equations for the different experimental conditions. We strongly believe that this approach is sufficiently accurate and experimentally feasible for this separation to be a valuable tool when developing a UHPLC method. After further validation with other separation systems, it could become a useful approach in UHPLC method development, especially in the pharmaceutical industry where demands are high for robustness and regulatory oversight.

  • 93.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enmark, Martin
    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.
    An Experimental and Theoretical investigation on Mobile PhaseEffects on Competitive Adsorption Isotherms in Preparative LC2012Conference paper (Refereed)
    Abstract [en]

    This poster serves as background information to the corresponding lecture. Mobile phase gradients have been used in LC since the 1950s and are still an important programming technique in both analytical and preparative LC. Improving the resolution, and thereby making the separation of complex samples possible, and reducing the separation time, which increases the productivity, are the two main advantages of gradient elution. The modelling of band profiles and the optimization of preparative separations has largely been studied under isocratic conditions. The shape of the gradient and the behaviour of the solutes are often determined experimentally with scarce knowledge about the underlying physicochemical equations. This "trial and error" approach results in time consuming and, possibly, expensive experiments. The goal of this work is to investigate the dependence of the adsorption behaviour on the mobile phase composition in reversed phase LC. By knowing the adsorption isotherm as a function of the concentrations of both the solute and the strong organic modifier, the band profiles are modelled under gradient elution conditions.Our aim is to make it possible to use modelling tools so one can optimize a separation and especially the gradient shape. Recent studies have shown that a significant improvement in productivity can be achieved if the gradient shapes are designed carefully [1,2].In this study we discuss how to obtain the adsorption isotherm data experimentally for two substances using the perturbation peak method. The substances which are investigated are cyclohexanone and cycloheptanone on a Kromasil C18-column with methanol-water as the mobile phase. The fitting of the nonlinear experimental data to appropriate theoretical isotherm models will also be discussed.For practical reasons, we will also be looking at how different key parameters, e.g. the column hold-up time, the column efficiency, the retention factor and the equilibrium constant, change with the mobile phase composition.With the experimentally determined adsorption isotherm as a basis, we will simulate overloaded band profiles under gradient elution conditions and compare the simulated results with experimentally obtained band profiles.A contribution from the Fundamental Separation Science Group www.separationscience.se

  • 94.
    Åsberg, Dennis
    et al.
    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).
    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).
    Evaluation of co-solvent fraction, pressure and temperature effects in analytical and preparative supercritical fluid chromatography2014In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1374, p. 254-260Article in journal (Refereed)
    Abstract [en]

    Abstract A chemometric approach is used for studying the combined effect of temperature, pressure and co-solvent fraction in analytical and preparative supercritical fluid chromatography (SFC). More specifically, by utilizing design of experiments coupled with careful measurements of the experimental conditions the interaction between pressure, temperature and co-solvent fraction was studied with respect to productivity, selectivity and retention in chiral SFC. A tris-(3,5-dimethylphenyl) carbamoyl cellulose stationary phase with carbon dioxide/methanol as mobile phase and the two racemic analytes trans-stilbene oxide (TSO) and 1,1′-bi-2-naphthol (BINOL) were investigated. It was found for the investigated model system that the co-solvent fraction and pressure were the parameters that most affected the retention factors and that the co-solvent fraction and column temperature were most important for controlling the selectivity. The productivity in the preparative mode of SFC was most influenced by the co-solvent fraction and temperature. Both high co-solvent fraction and temperature gave maximum productivity in the studied design space.

  • 95.
    Ņsberg, Dennis
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
    Enmark, Martin
    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.
    Modelling of Overloaded Gradient Elution in Reversed-Phase Liquid Chromatography2012Conference paper (Refereed)
    Abstract [en]

    Mobile phase gradients have been used in LC since the 1950s and are still an important programming technique in both analytical and preparative LC. Improving the resolution, and thereby making the separation of complex samples possible - and thus reducing the separation time which increases the productivity- are the two main advantages of gradient elution. The modelling of band profiles and the optimization of preparative separations has largely been studied under isocratic conditions. The shape of the gradient and the behaviour of the solutes are often determined experimentally with scarce knowledge about the underlying physicochemical equations. This “trial and error” approach results in time consuming and, possibly, expensive experiments. The goal of this work is to investigate the dependence of the adsorption behaviour on the mobile phase composition in reversed phase LC. By knowing the adsorption isotherm as a function of the concentrations of both the solute and the strong organic modifier, the band profiles can be modelled under gradient elution conditions. Our aim is to make it possible to use modelling tools for a more reliable computer-assisted optimization, accounting for the gradient shape. Recent studies have shown that a significant improvement in productivity can be achieved if the gradient shapes are designed carefully [1,2]. In this presentation we will discuss how to obtain the adsorption isotherm data experimentally for two substances using the perturbation peak method. The substances investigated are cyclohexanone and cycloheptanone on a system comprising of a Kromasil C18-column and methanol-water as mobile phase. The fitting of the nonlinear experimental data to appropriate theoretical isotherm models will also be discussed. For practical reasons, we will also be looking at how different key parameters, e.g. the column hold-up time, the column efficiency, the retention factor and the equilibrium constant, change with the mobile phase composition. With the experimentally determined adsorption isotherm as a basis, we will simulate overloaded band profiles under gradient elution conditions and compare the simulated results with experimentally obtained band profiles. A contribution from the Fundamental Separation Science Group www.separationscience.se

  • 96.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Karlsson, Anders
    AstraZeneca R and D, Mölndal, Sweden.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Kaczmarski, Krzysztof
    Poland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Analytical method development in the quality by design framework2014In: American Laboratory, ISSN 0044-7749, Vol. 46, no 9, p. 12-15Article in journal (Refereed)
    Abstract [en]

    The development of analytical methods in the Quality by Design (QbD) framework is currently gaining great momentum in the pharmaceutical industry. Presented here is a case study in which a pharmaceutical Quality Control (QC) method was developed using HPLC. The possibilities of continuous improvements during the method’s lifetime are demonstrated by switching to ultrahigh performance liquid chromatography (UHPLC).

  • 97.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lesko, Marek
    Rzeszow University of Technology.
    Enmark, Martin
    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.
    Forssén, Patrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Kaczmarski, Krzysztof
    Rzeszow University of Technology.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Prediction of Overloaded Profiles in Gradient Elution Chromatography2013Conference paper (Other academic)
    Abstract [en]

    This poster is a compliment to the oral presentation “A new procedure for improved predictions of overloaded profiles in gradient elution”. In order to simulate the separation process in liquid chromatography the competitive adsorption isotherms need to be known. In gradient elution the adsorption isotherms are determined with isocratic experiments on different mobile-phase plateaus that covers the range used in the gradient program. This can lead to extreme retention times for some mobile-phase compositions and therefore it might even be impossible to determine all necessary adsorption data using the traditional isocratic approach. We present a method where single and competitive nonlinear adsorption isotherms are determined directly from overloaded elution profiles in gradient elution. The numerical coefficients in the adsorption isotherms are determined by the inverse method that minimizes the difference between the calculated and the experimental elution profiles. This is an extension of the inverse method where the need for tedious/impossible isocratic experiments is eliminated. The method is systematically verified using both synthetic and experimental data. Finally the new method is used to successfully predict elution profiles for a two-component mixture in gradient elution. The new method makes it possible to study the adsorption of substances whose retention factor vary strongly with the mobile-phase composition, like peptides and proteins, where the classic methods will fail. A similar situation occurs in SFC and the proposed approach could with modifications probably be used also there. This is a contribution from the Fundamental Separation Science Group www.FSSG.se

  • 98.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Lesko, Marek
    Leek, Tomas
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Kaczmarski, Krzysztof
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Estimation of Nonlinear Adsorption Isotherms in Gradient Elution RP-LC of Peptides in the Presence of an Adsorbing Additive2017In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 80, no 6, p. 961-966Article in journal (Refereed)
    Abstract [en]

    In electrostatic repulsive interaction chromatography, using a charged surface hybrid sorbent carrying positive charges can improve the peak shape of peptides in reversed-phase liquid chromatography (RP-LC), especially in overloaded conditions, compared with standard C-18 sorbents. However, the positive surface charges can interact with anionic additives commonly used in peptide separations, e.g., trifluoroacetic acid (TFA), complicating adsorption isotherm estimation. We investigated how the competition for available adsorption sites between TFA and two peptides influenced the adsorption isotherm in gradient elution. A model accounting for the competition with TFA was compared with a model neglecting TFA adsorption. We found that the two models predicted elution profiles with the same accuracy. We also found that the adsorption isotherms were extremely similar in shape, leading to the conclusion that neglecting the competition with TFA is a valid approximation enabling faster and more robust adsorption isotherm estimation for the studied type of sorbent.

  • 99.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Leśko, Marek
    Department of Chemical Engineering, Rzeszów University of Technology, Rzeszów, Poland.
    Enmark, Martin
    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.
    Kaczmarski, Krzysztof
    Department of Chemical Engineering, Rzeszów University of Technology, Rzeszów, Poland.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fast estimation of adsorption isotherm parameters in gradient elution preparative liquid chromatography. I: The single component case2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1299, p. 64-70Article in journal (Refereed)
    Abstract [en]

    The inverse method is a numeric method for fast estimation of adsorption isotherm parameters directly from overloaded elution profiles. However, it has previously only been used for isocratic experiments. Here we will extend the inverse method so it can be used for gradient elution too. This extended inverse method will make it possible to study the adsorption of substances whose retention factor vary strongly with the mobile-phase composition, like peptides and proteins, where the classic methods will fail. Our extended inverse method was verified using both simulations and real experiments. For simulated overloaded elution profiles we were able to determine almost exact Langmuir adsorption isotherm parameters with the new approach. From real experimental data, bi-Langmuir adsorption parameters were estimated using both the perturbation peak method and the extended inverse method. The shape of the acquired adsorption isotherms did match over the considered concentration range; however, the adsorption isotherm parameters found with the two methods were not the same. This is probably due to the fact that adsorption isotherm estimated with the inverse method is only a good approximation up to the highest eluted concentration in the used chromatograms. But this is not a serious drawback from a process point of view where the main objective is to make accurate predictions of elution profiles. The bi-Langmuir adsorption isotherm obtained with both methods could accurately predict the shape of overloaded elution profiles.

  • 100.
    Åsberg, Dennis
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Leśko, Marek
    Department of Chemical and Process Engineering, Rzeszów University of Technology.
    Enmark, Martin
    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.
    Kaczmarski, Krzysztof
    Department of Chemical and Process Engineering, Rzeszów University of Technology.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fast estimation of adsorption isotherm parameters in gradient elution preparative liquid chromatography. II: The competitive case2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1314, no Nov, p. 70-76Article in journal (Refereed)
    Abstract [en]

    Abstract Experimental competitive adsorption isotherms were successfully determined directly from overloaded elution profiles in gradient elution mode using an extended inverse method. This approach differs from the existing methods in one important aspect – no isocratic experiments are necessary which makes it possible to study adsorption of substances whose retention factors vary strongly with the mobile-phase composition. The approach was verified with simulated binary data and with experimental data from gradient separations of a cyclohexanone/cycloheptanone mixture. For the synthetic data, the original adsorption isotherm parameters were found using a two-step estimation procedure. In the first step analytical peaks were used to estimate the “analytical” part of the Langmuir equation and in the second step the association equilibrium parameters were estimated from two simulated overloaded elution profiles. For the experimental data, a three-step approach was used. The two first steps were used to reduce the calculation time so that parameter estimation could be performed on an ordinary computer. In the first step, analytical peaks were used to estimate the “analytical” part of the bi-Langmuir equation. In the second step, initial guesses for all other parameters were determined separately for each solute using the faster Rouchon algorithm. In the final and third step, the more accurate orthogonal collocation on finite elements algorithm, was used to fine-tune the isotherm parameters. The model could accurately predict the shape of overloaded elution profiles. The shape of the adsorption isotherms agreed well with those determined with the standard isocratic method, although the numerical values were not the same. The extended inverse method is well suited for process optimization where few experiments and accurate predictions are important.

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