The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Torgny Fornstedt - One of the best experts on this subject based on the ideXlab platform.
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Combining Chemometric Models with Adsorption Isotherm Measurements to Study Omeprazole in RP-LC.
Chromatographia, 2016Co-Authors: Dennis Åsberg, Jörgen Samuelsson, Krzysztof Kaczmarski, Marek Leśko, Anders Karlsson, Torgny FornstedtAbstract:The Adsorption of the proton-pump inhibitor omeprazole was investigated using RP-LC with chemometric models combined with Adsorption Isotherm modelling to study the effect of pH and type of organic modifier (i.e., acetonitrile or methanol). The chemometric approach revealed that omeprazole was tailing with methanol and fronting with acetonitrile along with increased fronting at higher pH. The increased fronting with higher pH for acetonitrile was explored using a pH-dependent Adsorption Isotherm model that was determined using the inverse method and it agreed well with the experimental data. The model indicated that the peaks exhibit more fronting at high pH due to a larger fraction of charged omeprazole molecules. This model could accurately predict the shape of elution profiles at arbitrary pH levels in the studied interval. Using a two-layer Adsorption Isotherm model, the difference between acetonitrile and methanol was studied at the lowest pH at which almost all omeprazole molecules are neutral. Omeprazole had adsorbate-adsorbate interactions that were similar in strength for the acetonitrile and methanol mobile phases, while the solute-adsorbent interactions were almost twice as strong with methanol. The difference in the relative strengths of these two interactions likely explains the different peak asymmetries (i.e., tailing/fronting) in methanol and acetonitrile. In conclusion, thermodynamic modelling can complement chemometric modeling in HPLC method development and increase the understanding of the separation.
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Choice of Model for Estimation of Adsorption Isotherm Parameters in Gradient Elution Preparative Liquid Chromatography.
Chromatographia, 2015Co-Authors: Marek Leśko, Torgny Fornstedt, Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Krzysztof KaczmarskiAbstract: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.
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fast estimation of Adsorption Isotherm parameters in gradient elution preparative liquid chromatography i the single component case
Journal of Chromatography A, 2013Co-Authors: Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Krzysztof Kaczmarski, Marek Leśko, Torgny FornstedtAbstract: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.
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impact of an error in the column hold up time for correct Adsorption Isotherm determination in chromatography i even a small error can lead to a misunderstanding of the retention mechanism
Journal of Chromatography A, 2008Co-Authors: Jörgen Samuelsson, Peter Sajonz, Torgny FornstedtAbstract:The impact of a realistic error in the column hold-up time on the determination of the Adsorption Isotherm model was systematically investigated. Frontal analysis and the inverse method were used for the accurate determination of the Adsorption Isotherm. The true retention times of the breakthrough curves were used with a known hold-up time as reference. The Adsorption Isotherms were calculated using the same procedure that is used for real experimental Adsorption Isotherms, where the true hold-up time is unknown. The raw data were analyzed with calculations of Adsorption energy distributions (AEDs), Scatchard plots, fitting to different rival Adsorption models and finally their ability to predict true profiles. The results show that for a true Langmuir and bi-Langmuir model with an underestimated hold-up time the error may lead to a more heterogeneous model and for overestimated cases false Adsorption processes like multi-layer Adsorption or solute-solute interaction are assumed. The Scatchard plots for data obtained using a Langmuir Adsorption Isotherm are nonlinear and the AEDs show clear deviations from Langmuir behavior already at small deviations from the true hold-up time at a moderate surface coverage. The inverse method confirms the result that was obtained from the frontal analysis procedure.
Andreas Seidelmorgenstern - One of the best experts on this subject based on the ideXlab platform.
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design of the simulated moving bed process based on Adsorption Isotherm measurements using a perturbation method
Journal of Chromatography A, 1998Co-Authors: Christian Heuer, Ernst Kusters, Thomas Plattner, Andreas SeidelmorgensternAbstract:Abstract The design of a simulated moving bed (SMB) chromatography process for the enantioseparation of 1-phenoxy-2-propanol with Chiralcel OD as stationary phase is described using equilibrium theory and a dispersion model. The most essential prerequisite for reliable process simulation is the proper experimental determination of the corresponding Adsorption Isotherms. This paper evolved from the need to: (i) elaborate a technique for Adsorption Isotherm measurement based on a perturbation method; and (ii) to demonstrate the applicability of the equilibrium-dispersion model for quick process design. The accuracy of the obtained Adsorption Isotherms was evaluated by comparison with results that have been obtained independently using the classical Adsorption–desorption procedure. As the main result, it turned out that the suggested SMB design concept based both on Adsorption Isotherms measured with the perturbation method and on the equilibrium-dispersion model could be verified experimentally.
Jörgen Samuelsson - One of the best experts on this subject based on the ideXlab platform.
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Combining Chemometric Models with Adsorption Isotherm Measurements to Study Omeprazole in RP-LC.
Chromatographia, 2016Co-Authors: Dennis Åsberg, Jörgen Samuelsson, Krzysztof Kaczmarski, Marek Leśko, Anders Karlsson, Torgny FornstedtAbstract:The Adsorption of the proton-pump inhibitor omeprazole was investigated using RP-LC with chemometric models combined with Adsorption Isotherm modelling to study the effect of pH and type of organic modifier (i.e., acetonitrile or methanol). The chemometric approach revealed that omeprazole was tailing with methanol and fronting with acetonitrile along with increased fronting at higher pH. The increased fronting with higher pH for acetonitrile was explored using a pH-dependent Adsorption Isotherm model that was determined using the inverse method and it agreed well with the experimental data. The model indicated that the peaks exhibit more fronting at high pH due to a larger fraction of charged omeprazole molecules. This model could accurately predict the shape of elution profiles at arbitrary pH levels in the studied interval. Using a two-layer Adsorption Isotherm model, the difference between acetonitrile and methanol was studied at the lowest pH at which almost all omeprazole molecules are neutral. Omeprazole had adsorbate-adsorbate interactions that were similar in strength for the acetonitrile and methanol mobile phases, while the solute-adsorbent interactions were almost twice as strong with methanol. The difference in the relative strengths of these two interactions likely explains the different peak asymmetries (i.e., tailing/fronting) in methanol and acetonitrile. In conclusion, thermodynamic modelling can complement chemometric modeling in HPLC method development and increase the understanding of the separation.
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Choice of Model for Estimation of Adsorption Isotherm Parameters in Gradient Elution Preparative Liquid Chromatography.
Chromatographia, 2015Co-Authors: Marek Leśko, Torgny Fornstedt, Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Krzysztof KaczmarskiAbstract: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.
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fast estimation of Adsorption Isotherm parameters in gradient elution preparative liquid chromatography i the single component case
Journal of Chromatography A, 2013Co-Authors: Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Krzysztof Kaczmarski, Marek Leśko, Torgny FornstedtAbstract: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.
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impact of an error in the column hold up time for correct Adsorption Isotherm determination in chromatography i even a small error can lead to a misunderstanding of the retention mechanism
Journal of Chromatography A, 2008Co-Authors: Jörgen Samuelsson, Peter Sajonz, Torgny FornstedtAbstract:The impact of a realistic error in the column hold-up time on the determination of the Adsorption Isotherm model was systematically investigated. Frontal analysis and the inverse method were used for the accurate determination of the Adsorption Isotherm. The true retention times of the breakthrough curves were used with a known hold-up time as reference. The Adsorption Isotherms were calculated using the same procedure that is used for real experimental Adsorption Isotherms, where the true hold-up time is unknown. The raw data were analyzed with calculations of Adsorption energy distributions (AEDs), Scatchard plots, fitting to different rival Adsorption models and finally their ability to predict true profiles. The results show that for a true Langmuir and bi-Langmuir model with an underestimated hold-up time the error may lead to a more heterogeneous model and for overestimated cases false Adsorption processes like multi-layer Adsorption or solute-solute interaction are assumed. The Scatchard plots for data obtained using a Langmuir Adsorption Isotherm are nonlinear and the AEDs show clear deviations from Langmuir behavior already at small deviations from the true hold-up time at a moderate surface coverage. The inverse method confirms the result that was obtained from the frontal analysis procedure.
Jessica M Rosenholm - One of the best experts on this subject based on the ideXlab platform.
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modeling of a hybrid langmuir Adsorption Isotherm for describing interactions between drug molecules and silica surfaces
Journal of Pharmaceutical Sciences, 2017Co-Authors: Thomas Sandberg, Christian Weinberger, Didem şen Karaman, Jessica M RosenholmAbstract:Abstract The interaction between disulfiram (Antabus ® ) and silica was studied experimentally by Adsorption from apolar solvent onto highly porous silica material (Santa Barbara amorphous material-3) with large surface area. The Adsorption Isotherm was fitted to the Langmuir model by accounting 2 different affinities contributing to the overall behavior, which were attributed to 2 different types of silanol groups (i.e., geminal and vicinal) present on amorphous silica surfaces. This assumption was supported by theoretical calculations. In addition, the model could describe the Adsorption of ibuprofen to the carrier material, indicating that the model bears big potential for describing the interactions between silica surfaces and drug molecules.
Toshiya Sakata - One of the best experts on this subject based on the ideXlab platform.
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potentiometric Adsorption Isotherm analysis of a molecularly imprinted polymer interface for small biomolecule recognition
ACS omega, 2018Co-Authors: Shoichi Nishitani, Toshiya SakataAbstract:In this paper, we report a direct and quantitative analytical method of small-biomolecule recognition with a molecularly imprinted polymer (MIP) interface, taking advantage of the potentiometric principle of a field-effect transistor (FET) sensor, which enables the direct detection of ionic charges without using labeling materials such as fluorescent dyes. The interaction of low-molecular-weight oligosaccharides such as paromomycin and kanamycin with the MIP interface including phenylboronic acid (PBA) was directly and quantitatively analyzed from the electrical signals of an MIP-coated FET sensor. In particular, the change in the potential response of the FET sensor was derived on the basis of the multi-Langmuir Adsorption Isotherm equations, considering the change in the molecular charges of PBA caused by the Adsorption equilibrium of the analytes with the vinyl PBA-copolymerized MIP membrane. Thus, the potentiometric Adsorption Isotherm analysis can elucidate the formation of selective binding sites at...
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Potentiometric Adsorption Isotherm Analysis of a Molecularly Imprinted Polymer Interface for Small-Biomolecule Recognition
2018Co-Authors: Shoichi Nishitani, Toshiya SakataAbstract:In this paper, we report a direct and quantitative analytical method of small-biomolecule recognition with a molecularly imprinted polymer (MIP) interface, taking advantage of the potentiometric principle of a field-effect transistor (FET) sensor, which enables the direct detection of ionic charges without using labeling materials such as fluorescent dyes. The interaction of low-molecular-weight oligosaccharides such as paromomycin and kanamycin with the MIP interface including phenylboronic acid (PBA) was directly and quantitatively analyzed from the electrical signals of an MIP-coated FET sensor. In particular, the change in the potential response of the FET sensor was derived on the basis of the multi-Langmuir Adsorption Isotherm equations, considering the change in the molecular charges of PBA caused by the Adsorption equilibrium of the analytes with the vinyl PBA-copolymerized MIP membrane. Thus, the potentiometric Adsorption Isotherm analysis can elucidate the formation of selective binding sites at the MIP interface. The electrochemical analysis of the functional biointerface used in this study supports the design and construction of sensors for small biomarkers
