| 1. |
- Fornstedt, Torgny, et al.
(författare)
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New Procedure for Predictions of Overloaded Profiles in Gradient Elution
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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, levels covering 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. In this talk, we will 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 calculated and experimental elution profiles. This is a new 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 open up the opportunity 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. We also intend to transfer the metholology for SFC in near future; but there are some problems to be solved first (see our SFC posters). This is a contribution from the Fundamental Separation Science Group www.FSSG.se
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| 2. |
- Åsberg, Dennis, et al.
(författare)
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Fast estimation of adsorption isotherm parameters in gradient elution preparative liquid chromatography. I : The single component case
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1299, s. 64-70
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Åsberg, Dennis, et al.
(författare)
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Fast estimation of adsorption isotherm parameters in gradient elution preparative liquid chromatography. II : The competitive case
- 2013
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1314:Nov, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 4. |
- Åsberg, Dennis, 1998-, et al.
(författare)
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Method transfer from high-pressure liquid chromatography to ultra-high-pressure liquid chromatography. I. A thermodynamic perspective
- 2014
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1362, s. 206-217
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Tidskriftsartikel (refereegranskat)abstract
- This is the first investigation in a series that aims to enhance the scientific knowledge needed for reliable analytical method transfer between HPLC and UHPLC using the quality by design (QbD) framework. Here, we investigated the differences and similarities from a thermodynamic point of view between RP-LC separations conducted with 3.5 μm (HPLC) and 1.7 μm (UHPLC) C18 particles. Three different model solutes and one pharmaceutical compound were used: the uncharged cycloheptanone, the cationic benzyltriethylammonium chloride, the anionic sodium 2-naphatlene sulfonate and the pharmaceutical compound omeprazole, which was anionic at the studied pH. Adsorption data were determined for the four solutes at varying fractions of organic modifier and in gradient elution in both the HPLC and UHPLC system, respectively. From the adsorption data, the adsorption energy distribution of each compound was calculated and the adsorption isotherm model was estimated. We found that the adsorption energy distribution was similar, with only minor differences in degree of homogeneity, for HPLC and UHPLC stationary phases. The adsorption isotherm model did not change between HPLC and UHPLC, but the parameter values changed considerably especially for the ionic compounds. The dependence of the organic modifier followed the same trend in HPLC as in UHPLC. These results indicates that the adsorption mechanism of a solute is the same on HPLC and UHPLC stationary phases which simplifies design of a single analytical method applicable to both HPLC and UHPLC conditions within the QbD framework.
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| 5. |
- Åsberg, Dennis, et al.
(författare)
-
Prediction of Overloaded Profiles in Gradient Elution Chromatography
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This poster is a compliment to the oral presentation “A new procedure for improved predictions of overloaded profiles in gradient elutionâ€. 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
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