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Molecular Weight Cut-off (molecular + weight_cut-off)
Selected AbstractsAssessment of a semi-quantitative method for estimation of the rejection of organic compounds in aqueous solution in nanofiltrationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Bart Van der Bruggen Abstract A large number of different mechanisms describing the retention of dissolved organic compounds in nanofiltration have been proposed. A recent review identified the parameters possibly involved in the separation performance and suggested a qualitative classification of dissolved compounds. Continuing this approach, a semi-quantitative assessment of the observed rejections in nanofiltration is given in this paper, based on threshold values of key parameters such as molecular weight and molecular weight cut-off (MWCO), molecular size, pH and pKa, hydrophobicity (logKow) and membrane charge. Experimental values and literature data were used to provide a broad basis for comparison. It was concluded that (a) all categories that contain hydrophobic components are badly defined, in particular for small components, with rejections varying from low to very high, (b) all components that contain hydrophilic components have relatively high rejections and (c) all categories that contain charged components have well-defined, high rejections (intermediate for membranes with low surface charge). In all cases, the average rejection is higher when the component's molecular weight is larger than the MWCO of the membrane and when the molecular size is larger than the pore size of the membrane. Copyright © 2006 Society of Chemical Industry [source] QUANTIFICATION OF FLUX DECLINE OF DEPECTINIZED MOSAMBI (CITRUS SINENSIS[L.] OSBECK) JUICE USING UNSTIRRED BATCH ULTRAFILTRATIONJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2005P. RAI ABSTRACT Ultrafiltration of enzymatically treated mosambi (Citrus sinensis [L.] Osbeck) juice was performed in a batch, unstirred membrane cell. Thin film composite polyamide membrane of molecular weight cut-off 50,000 was used. The flux-decline mechanism was identified by the growth of a gel-type layer over the membrane surface. The flux decline, the gel resistance, the gel-layer thickness and various domains of resistances were calculated at a constant pressure difference in the range of 276,552 kPa. The conventional gel-filtration theory was employed to analyze the flux-decline behavior. The calculated permeate flux and gel-layer resistances were consistent with the experimental results. The calculated gel-layer thickness varied from 4.12 to 74.1 µm for different operating condition (pressure) and time. The time at which the gel resistance becomes equal to the membrane-hydraulic resistance ranged from 13 to 31 s for the pressure range studied herein. Thus, the deposited layer resistance to permeate flow was substantial, throughout the whole operation, except in the first few seconds. [source] Scaleable purification process for gene therapy retroviral vectorsTHE JOURNAL OF GENE MEDICINE, Issue 4 2007Teresa Rodrigues Abstract Background Retroviral vectors (RVs) constitute one of the preferred gene therapy tools against inherited and acquired diseases. Development of scaleable downstream processes allowing purification under mild conditions and yielding viral preparations with high titer, potency and purity is critical for the success of clinical trials and subsequent clinical use of this technology. Methods A purification process for murine leukaemia virus (MLV)-derived vector supernatants was developed based on membrane separation and anion-exchange chromatography (AEXc). Initial clarification of the vector stocks was performed using 0.45 µm membranes followed by concentration with 500 kDa molecular weight cut-off (MWCO) membranes; further purification was performed by AEXc using a tentacle matrix bearing DEAE functional ligands. Finally, concentration/diafiltration was performed by 500 kDa MWCO membranes. To validate final product quality the process was scaled up 16-fold. Results Optimization of microfiltration membrane pore size and ultrafiltration transmembrane pressure allowed the recovery of nearly 100% infectious particles. Further purification of the RVs by AEXc resulted in high removal of protein contaminants while maintaining high recoveries of infectious vectors (77 ± 11%). Up-scaling of the process resulted in high titer vector preparations, 3.2 × 108 infectious particles (IP)/ml (85-fold concentration), with an overall recovery reaching 26%. The process yielded vectors with transduction efficiencies higher than the starting material and more than 99% pure, relative to protein contamination. Conclusions The combination of membrane separation and AEXc processes results in a feasible and scaleable purification strategy for MLV-derived vectors, allowing the removal of inhibitory contaminants thus yielding pure vectors with increased transduction efficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimization of mass transfer for toxin removal and immunoprotection of hepatocytes in a bioartificial liverBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Geir I. Nedredal Abstract This study was designed to determine optimal operating conditions of a bioartificial liver (BAL) based on mass transfer of representative hepatotoxins and mediators of immune damage. A microprocessor-controlled BAL was used to study mass transfer between patient and cell compartments separated by a hollow fiber membrane. Membrane permeability (70, 150, or 400,kDa molecular weight cut-off,MWCO), membrane convection (high: 50,mL/min; medium: 25,mL/min; low: 10,mL/min; diffusion: 0,mL/min), and albumin concentration in the cell compartment (0.5 or 5,g%) were considered for a total of 24 test conditions. Initially, the patient compartment contained pig plasma supplemented with ammonia (0.017,kDa), unconjugated bilirubin (0.585,kDa), conjugated bilirubin (0.760,kDa), TNF-, (17,kDa), pig albumin (67,kDa), pig IgG (147,kDa), and pig IgM (900,kDa). Mass transfer of each substance was determined by its rate of appearance in the cell compartment. Membrane fouling was assessed by dextran polymer technique. Of the three tested variables (membrane pore size, convection, and albumin concentration), membrane permeability had the greatest impact on mass transfer (P,<,0.001). Mass transfer of all toxins was greatest under high convection with a 400,kDa membrane. Transfer of IgG and IgM was insignificant under all conditions. Bilirubin transfer was increased under high albumin conditions (P,=,0.055). Fouling of membranes ranged from 7% (400,kDa), 24% (150,kDa) to 62% (70,kDa) during a 2-h test interval. In conclusion, optimal toxin removal was achieved under high convection with a 400-kDa membrane, a condition which should provide adequate immunoprotection of hepatocytes in the BAL. Biotechnol. Bioeng. 2009; 104: 995,1003. © 2009 Wiley Periodicals, Inc. [source] Physico-Chemical Characterization of Nanofiltration MembranesCHEMPHYSCHEM, Issue 3 2007Katleen Boussu Abstract This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25,1.55 Å as well as a pore size of 3.20,3.95 Å (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly. [source] Ultrafiltration of industrial waste liquors from the manufacture of soy protein concentratesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Andrés Moure Abstract Protein-containing waste liquors from the manufacture of soy protein concentrates were processed by ultrafiltration to recover soluble protein using three different membranes (with molecular weight cut-offs of 10, 30 and 50 kDa). Operating at 20 °C under reversible conditions, the experimental data of the normalized permeate flux (NPF) obtained at various transmembrane pressures were well described by a model reported in the literature. For each membrane and transmembrane pressure, the values of the parameters involved in the model were calculated. Operating at selected transmembrane pressures, protein rejections of 0.705, 0.747 and 0.637 were determined for the 10, 30 and 50 kDa membranes, respectively. Operation with the 10 kDa membrane at temperatures in the range 30,50 °C and operation with the 30 or 50 kDa membranes at 40 or 50 °C resulted in hysteresis. Copyright © 2006 Society of Chemical Industry [source] | |||||||||||||