| 1. |
- Degerman, Marcus, et al.
(författare)
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Constrained optimization of a preparative ion-exchange step for antibody purification
- 2006
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1113:1-2, s. 92-100
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Tidskriftsartikel (refereegranskat)abstract
- Today, the optimization of chromatographic separation is usually based on experimental work and rule of thumb. The process and analytical technology (PAT) initiative, of the US Food and Drug Administration, has provided the opportunity of using model-based approach when designing downstream processing of pharmaceutical substances. A nonlinear chromatography model was used in this study to optimize a preparative ion-exchange separation step involving two components. Separation was simulated with the general rate model employing Langmuir kinetics. Optimization was performed with an indirect method allowing constraints on the purity, thus avoiding sub-optimization, which can lead to noisy objective functions. The six decision variables used in the optimizations were flow rate, loading volume, initial salt concentration in the elution, final salt concentration in the linear elution gradient and the two cut points. A graphical representation of the effect of the decision variables on the objective function was used to verify that the optimization had converged to the true optimum. The optimal operating points, using productivity and yield separately as objective functions, were found and compared with the product of productivity and yield as objective function. The optimum obtained with this objective function had a lower productivity, than the productivity function, but much higher yield, which makes it a good substitute for a cost function. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Degerman, Marcus, et al.
(författare)
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Modeling and optimization of preparative reversed-phase liquid chromatography for insulin purification
- 2007
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1162:1, s. 41-49
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a model for reversed-phase purification of insulin from desamido insulin. The system is described by a reaction dispersive model with a competitive Langmuir isotherm. A model building and calibration method is presented and the model's region of validity is defined. The model is calibrated using only two-component experiments on the raw mixture by the inverse method and then experimentally validated. The model is then used to optimize the system's production rate with both purity and yield requirements. The yield requirement is varied between 80 and 95% to study the effect on the production rate and the operating point. The operating points found with the optimization were found outside the model's region of validity, but the experimental validation of the operating points shows that the model can be extrapolated to the interesting operating points. (c) 2007 Elsevier B.V. All rights reserved.
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| 3. |
- Jakobsson, Niklas, et al.
(författare)
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Model based robustness analysis of an ion-exchange chromatography step
- 2007
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1138:1-2, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Process development, optimization and robustness analysis for chromatographic separation are often entirely based on experimental work and generic knowledge. This paper describes a model-based approach that can be used to am process knowledge and assist in the robustness analysis of an ion-exchange chromatography step using a model-based approach. A kinetic dispersive model, where the steric mass action model accounts for the adsorption is used to describe column performance. Model calibration is based solely on gradient elution experiments at different gradients, flow rates, pH and column loads. The position and shape of the peaks provide enough information to calibrate the model and thus single-component experiments can be avoided. The model is calibrated to the experiments and the confidence intervals for the estimated parameters are used to account for the model error throughout the analysis. The model is used to predict the result of a robustness analysis conducted as a factorial experiment and to design a robust pooling approach. The confidence intervals are used in a "worst case" approach where the parameters for the components are set at the edge of their confidence intervals to create a worst case for the removal of impurities at each point in the factorial experiment. The pooling limit was changed to ensure product quality at every point in the factorial analysis. The predicted purities and yields were compared to the experimental results to ensure that the prediction intervals cover the experimental results. (c) 2006 Elsevier B.V. All rights reserved.
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| 4. |
- Jakobsson, Niklas, et al.
(författare)
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Optimisation and robustness analysis of a hydrophobic interaction chromatography step
- 2005
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 118:Supplement 1, s. 61-61
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Tidskriftsartikel (refereegranskat)abstract
- Process development, optimisation and robustness analysis for chromatography separations are often entirely based on experimental work and generic knowledge. The present study proposes a method of gaining process knowledge and assisting in the robustness analysis and optimisation of a hydrophobic interaction chromatography step using a model-based approach. Factorial experimental design is common practice in industry today for robustness analysis. The method presented in this study can be used to find the critical parameter variations and serve as a basis for reducing the experimental work. In addition, the calibrated model obtained with this approach is used to find the optimal operating conditions for the chromatography column. The methodology consists of three consecutive steps. Firstly, screening experiments are performed using a factorial design. Secondly, a kinetic-dispersive model is calibrated using gradient elution and column load experiments. Finally, the model is used to find optimal operating conditions and a robustness analysis is conducted at the optimal point. The process studied in this work is the separation of polyclonal IgG from BSA using hydrophobic interaction chromatography.
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| 5. |
- Jakobsson, Niklas, et al.
(författare)
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Using computer simulation to assist in the robustness analysis of an ion-exchange chromatography step
- 2005
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1063:1-2, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a methodology to gain process knowledge and assist in the robustness analysis of an ion-exchange step in a protein purification process using a model-based approach. Factorial experimental design is common practice in industry today to obtain robustness characterization of unit operations with respect to variations in process parameters. This work aims at providing a better insight into what process variations affect quality and to further reduce the experimental work to the regions of process variation that are of most interest. This methodology also greatly increases the ability to predict process performance and promotes process understanding. The model calibration part of the methodology involves three consecutive steps to calibrate a steric mass action (SMA) ion-exchange chromatography model. Firstly, a number of gradient elution experiments are performed. Secondly, experimental breakthrough curves have to be generated for the proteins if the adsorption capacity of the medium for each component is not known. Thirdly, a multi-component loading experiment is performed to calibrate the multi-component effects that cannot be determined from the single-component experiments. The separation process studied in this work is the separation of polyclonal IgG from a mixture containing IgG, myoglobin and BSA. The calibrated model is used to simulate six process variations in a full factorial experiment. The results of the simulations provide information about the importance of the different process variations and the simulations are also used to determine the crucial points for the process parameter variations. The methodology can be used to assist in the robustness analysis normally performed in the pharmaceutical industry today as it is able to predict the impact on process performance resulting from variations in salt concentration, column load, protein concentration and flow rate. (C) 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Karlsson, David, et al.
(författare)
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Methodologies for model calibration to assist the design of a preparative ion-exchange step for antibody purification
- 2004
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1033:1, s. 71-82
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Tidskriftsartikel (refereegranskat)abstract
- This work proposes methodologies using a model-based approach to gain knowledge on and assist the development of an ion-exchange step in a protein purification process; the separation of IgG from a mixture containing IgG, insulin and transferrin. This approach is suitable for capture and intermediate steps in a process. Both methods involve four consecutive steps. Firstly, the retention of the different protein components is determined giving a retention map of the system. From this the optimal pH and buffer can be determined. Secondly, additional salt gradient experiments are performed at the selected pH. Thirdly, experimental breakthrough curves have to be generated for the protein if the adsorption capacity of the medium for each component is not known. Fourthly, a validation experiment is performed. In method 1, where the capacity for the medium is assumed to be known, the protein adsorption is described by Langmuir kinetics with a mobile phase modulator (MPM). In this description salt is considered to be inert. In method 2 the adsorption behavior is described by steric mass action (SMA), where the salt component competes with the proteins for the available binding sites. Both methods use a dispersion model to describe transport in the mobile phase in the column. The methods are able to predict the separation and loading behavior of the three components. The methods can, with reasonable accuracy, predict the breakthrough of transferrin in a mixture of insulin, IgG and transferrin. Method I requires fewer experiments and predicts the mean volume of breakthrough for the loading step in the validation experiment more accurately than method 2. On the other hand, method 2 has a better accuracy to predict the position of 10% breakthrough and the shape of the breakthrough curve. The methods suggested in this work are shown to be efficient in process development. Some additional experiments have to be performed to obtain the unknown parameters in the models. However, the predictability that is achieved results in less experimental work in the process design as a whole. (C) 2004 Elsevier B.V. All rights reserved.
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| 7. |
- Karlsson, David, et al.
(författare)
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Model-based optimization of a preparative ion-exchange step for antibody purification
- 2004
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1055:1-2, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- A method using a model-based approach to design and optimize an ion-exchange step in a protein purification process is proposed for the separation of IgG from a mixture containing IgG, BSA and myoglobin. The method consists of three steps. In the first step, the model is calibrated against carefully designed experiments. The chromatographic model describes the convective and dispersive flow in the column, the diffusion in the adsorbent particles, and the protein adsorption using Langmuir kinetics with mobile phase modulators (MPM). In the second step, the model is validated against a validation experiment and analyzed. In the third and final step, the operating conditions are optimized. In the optimization step, the loading volume and the elution gradient are optimized with regard to the most important costs: the fixed costs and the feed cost. The optimization is achieved by maximizing the objective functions productivity (i.e. the production rate for a given amount of stationary phase) and product yield (i.e. the fraction of IgG recovered in the product stream). All optimization is conducted under the constraint of 99% purity of the IgG. The model calibration and the analysis show that this purification step is determined mainly by the kinetics. although as large a protein as IgG is used in the study. The two different optima resulting from this study are a productivity of 2.7 g IgG/(s m(3)) stationary phase and a yield of 90%. This model-based approach also gives information of the robustness of the chosen operating conditions. It is shown that the bead diameter could only be increased from 15 mum to 35 mum with maximum productivity and a 99% purity constraint due to increased diffusion hindrance in larger beads. (C) 2004 Elsevier B.V. All rights reserved.
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