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Adsorption Isotherm

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Torgny Fornstedt – One of the best experts on this subject based on the ideXlab platform.

  • Combining Chemometric Models with Adsorption Isotherm Measurements to Study Omeprazole in RP-LC.
    Chromatographia, 2016
    Co-Authors: Dennis Åsberg, Marek Leśko, Krzysztof Kaczmarski, Jörgen Samuelsson, Anders Karlsson, Torgny Fornstedt
    Abstract:

    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 soluteadsorbent 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.

  • Choice of Model for Estimation of Adsorption Isotherm Parameters in Gradient Elution Preparative Liquid Chromatography.
    Chromatographia, 2015
    Co-Authors: Marek Leśko, Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Torgny Fornstedt, Krzysztof Kaczmarski
    Abstract:

    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 elutelution conditions. However, the inverse method in gradient elutelution is cumbersome due to the complex Adsorption Isotherm models found in gradient elutelution. 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.

  • fast estimation of Adsorption Isotherm parameters in gradient elution preparative liquid chromatography i the single component case
    Journal of Chromatography A, 2013
    Co-Authors: Dennis Åsberg, Marek Leśko, Krzysztof Kaczmarski, Martin Enmark, Jörgen Samuelsson, Torgny Fornstedt
    Abstract:

    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 elutelution 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.

Andreas Seidelmorgenstern – One of the best experts on this subject based on the ideXlab platform.

Jörgen Samuelsson – One of the best experts on this subject based on the ideXlab platform.

  • Combining Chemometric Models with Adsorption Isotherm Measurements to Study Omeprazole in RP-LC.
    Chromatographia, 2016
    Co-Authors: Dennis Åsberg, Marek Leśko, Krzysztof Kaczmarski, Jörgen Samuelsson, Anders Karlsson, Torgny Fornstedt
    Abstract:

    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.

  • Choice of Model for Estimation of Adsorption Isotherm Parameters in Gradient Elution Preparative Liquid Chromatography.
    Chromatographia, 2015
    Co-Authors: Marek Leśko, Dennis Åsberg, Martin Enmark, Jörgen Samuelsson, Torgny Fornstedt, Krzysztof Kaczmarski
    Abstract:

    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.

  • fast estimation of Adsorption Isotherm parameters in gradient elution preparative liquid chromatography i the single component case
    Journal of Chromatography A, 2013
    Co-Authors: Dennis Åsberg, Marek Leśko, Krzysztof Kaczmarski, Martin Enmark, Jörgen Samuelsson, Torgny Fornstedt
    Abstract:

    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.

Jessica M Rosenholm – One of the best experts on this subject based on the ideXlab platform.

  • modeling of a hybrid langmuir Adsorption Isotherm for describing interactions between drug molecules and silica surfaces
    Journal of Pharmaceutical Sciences, 2017
    Co-Authors: Thomas Sandberg, Christian Weinberger, Didem şen Karaman, Jessica M Rosenholm
    Abstract:

    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.