The effect of the pore structure and zeta potential of porous polymer monoliths on separation performance in ion-exchange mode
Department of Chemical Engineering, University of Missouri, Columbia, Missouri, United States Journal of Separation Science
(Impact Factor: 2.74).
03/2007; 30(5):648-57. DOI: 10.1002/jssc.200600421
Most often, in bioseparations involving charged macromolecules, the chromatographic systems have low Reynolds and high Peclet numbers. For such systems, an expression is developed and presented in this work for evaluating the throughput in polymeric monoliths where ion-exchange adsorption occurs, as a function of (i) the pressure drop along the length of the monolith, (ii) the functional form and width of the throughpore-size distribution of the monolith, and (iii) the magnitude of the zeta potential on the surface of the throughpores of the monolith. Gaussian and log-normal throughpore-size distributions whose mean throughpore-size and standard deviation values are based on experimentally measured throughpore-size distribution data by mercury porosimetry employed on polymeric monoliths are used in this work, and their effect on the throughput relative to that obtained from a polymeric monolith having a uniform throughpore-size distribution is studied for different values of the ratio of the standard deviation to the mean throughpore-size. The results indicate that relatively modest increases in the throughput, when compared with the throughput that could be achieved in a polymeric monolith having a uniform throughpore-size distribution, could be obtained in polymeric monoliths having disperse throughpore-size distributions, and the magnitude of the increase becomes larger when the disperse distribution is skewed to larger throughpore sizes. Furthermore, the results of this work indicate that, under certain conditions, relatively modest increases in the throughput of a charged analyte could also be achieved by altering the value of the zeta potential on the surface of the throughpores of the monolith. Due to the difficulties inherent in controlling the functional form and width of the throughpore-size distribution during the synthesis of polymeric monoliths, it would appear to be more practical to increase the value of the throughput of a charged analyte by altering the value of the zeta potential through prudent selection of the ion-exchange surface functional groups and fine-tuned with the pH of the mobile phase. Thus, for ion-exchange chromatography systems, the zeta potential could be considered an important parameter for column designers and operators to manipulate, since its alteration could increase the through-put of a charged analyte in polymeric monoliths or in columns packed with charged particles.
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- "(2) and (3) is equal to the sum of p w,I and p in,I (P I = p w,I + p in,I ). The dusty-gas model has the major advantage of not requiring detailed information     about the porous structure of the dried layer I; if one has a rather detailed information of the pore structure of the dried layer I obtained from high-resolution optical microscopy    methods, then pore network theory    could be used to determine even more accurately the transport of heat and mass in the porous dried layer I. An estimate for the value of Darcy's flow permeability, C 01 could be obtained from the Blake–Kozeny correlation  "
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ABSTRACT: A mathematical model is presented that can be used to study the heat and mass transfer mechanisms that determine the dynamic behavior of the primary and secondary drying stages of spray freeze drying (freeze drying of particle based materials) in trays and in vials on trays. Simulation results indicate that particle based materials require longer primary drying times than solution based materials (conventional freeze drying) due to (a) reductions in the heat and mass transfer capabilities of particle based materials, and (b) the development of a secondary porous dried layer near the surface of the lower heating plate during the primary drying stage of the spray freeze drying process. The results of spray freeze drying for the systems studied in this work indicate that the drying rate during the primary drying stage increases as (i) the product height decreases, (ii) the particle diameter increases, and (iii) the value of the packing porosity increases. The mathematical model presented in this work is considered to offer a necessary and essential capability that could be used for the design, optimization, and control of the spray freeze drying process as well as of a process involving the drying of frozen particles in packed beds.
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ABSTRACT: The mass transport of a charged analyte in ion-exchange mode from the flowing fluid stream in the channels for bulk flow in a packed bed of charged particles (or in the throughpores for bulk flow of a monolith) to the surface of the charged particles (or to the charged surfaces of the throughpores of a monolith) occurs by the mechanisms of convection, diffusion, and electrophoretic migration, and the theoretical expression for the film mass transfer coefficient, Kf, of a charged analyte involves parameters that have to be determined from experimental data. In this work, the type of chromatographic ion-exchange experiments and the data that have to be measured in the experiments together with two different methods for calculating the experimental values of the film mass transfer coefficient, Kf, as well as a procedure for determining the parameters of the theoretical expression for Kf are presented.
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ABSTRACT: Capillary electrochromatography suffered in its development because of difficulty in producing stable columns with good permeability. Variability in frit characteristics gave rise to non-reproducible capillaries whose fabrication was extremely difficult and time consuming. Monolithic stationary phases gained popularity in the early 1990s due to the fact that they were easy to fabricate and required no retaining frits. They were also able to be manufactured in a wide variety of chemistries which made them very interesting to the analytical chemist who is constantly looking for materials with different selectivity to the popular silica-based stationary phases.
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