Permeating speed

The permeating speed was obtained by the experiments using oxygen and nitrogen gases. The permeability constant and the permeating speed were determined as shown below. 

This application is based on the hydrophilicity of the ion exchange membrane. Though it is not essential to use an ion exchange membrane,219 they show excellent performance in pervaporation for dehydration of organic solvents. Pervaporation is the separation of solvents on the basis of their different affinities for the membrane and different permeation speeds through the membrane phase. The system consists of a liquid mixture to be separated, which contacts one side of the membrane, and a gas phase to permeate under reduced pressure, which is on the other side of the membrane (Figure 6.37). Membrane performance is evaluated by a permeability coefficient (flux) and separation factor (selectivity coefficient). The permeability coefficient, Q, is the permeated solvent through the membrane per unit area and unit time (kgm 2 h1). When a mixed solvent composed of components A and B is separated, the separation factor, a, is defined as... 

Attempts were made to determine number average molecular weights (Mn) by osmometry (Mechrolab Model 502, high speed membrane osmometer, 1 to 10 g/1 toluene solution at 37 °C), however, in many instances irreproducible data were obtained, probably due to the diffusion of low molecular weight polymer through the membrane. This technique was abandoned in favor of gel permeation chromatography (GPC). 

A bench top polysulfone hollow fiber membrane (0.0325m ) with molecular weight cutoff (MWCO) of 30K (A/G Technology Corp., Needham MA) was used (24). UF was run in a total recycle mode at a rate of 1.2 L/min (flow speed of 0.73 m/sec), cross membrane pressure of 25 PSIG and 10 + 1°C. PE permeability is expressed as the fraction of PEU/mL in the permeate to PEU/mL in the retentate. Data presented are representative of at least duplicate replications. 

Hashimoto, T., Sasaki, H., Aiura, M., and Kato, Y., High-speed aqueous gel-permeation chromatography, /. Polym. Sci. Polym. Phys. Ed., 16, 1789, 1978. 

High-Performance High-Speed Gel Permeation Chromatography... 

Efficiencies of 24,000 plates at permeation and 23,000 plates at total exclusion were measured at flow rates of 1.0 ml/minute for this column. Separation speed is quite good also, but does not represent the limit which can be attained. 

High efficiency columns currently available for gel permeation chromatography of small molecules and oligomers provide high speed separations. The use of multiple detectors provides additional information which facilitates characterization and determination of the separated species. 

Cotmnercial cellulose triacetate samples were fractionated by both fractional precipitation and preparative gel permeation chromatography (GPC). The triacetate fractions were characterized by vlsco-metry, high speed membrane osmometry (HSMO) and GPC. A fair agreement has been found between the molecular weights of various triacetate fractions determined by the three procedures. 

Diffusion (A). Lipophilic substances (red dots) may enter the membrane from the extracellular space (area shown in ochre), accumulate in the membrane, and exit into the cytosol (blue area). Direction and speed of permeation depend on the relative concentrations in the fluid phases and the membrane. The steeper the gradient (concentration difference), the more drug will be diffusing per unit of time (Pick s Law). The lipid membrane represents an almost insurmountable obstacle for hydrophilic substances (blue triangles). 

Experiments performed in vitro revealed that in contrast to DFO, which has a major cytotoxic effect only on trophozoites and early schizonts of P. falciparum, reversed siderophores have a cytotoxic effect on ring-stage and cytostatic effects on trophozoites and schizonts . These observations provided the basis for studying combinations of iron chelators for antimalarial therapy. When DFO is added to malaria parasites cultured in erythrocytes in combination with the more lipophilic and more permeate reversed siderophore 66, a strong synergistic inhibitory effect on parasite growth is observed. This effect may result from the different speeds of permeation of the two chelators... 

B.J. Gudzinowicz and K. Alden, High-speed gel permeation chromatography,... 

This handbook makes no attempt to describe environmental transport properties because these phenomena are specific to environmental conditions such as wind speed and water current velocity. A notable exception is the diffusion or permeation rate of a substance through biological membranes, which is the key process controlling dermal absorption and therefore a key determinant of the dose actually available to exert a toxic effect. Chapter 11 treats this topic. The reader seeking estimation methods for molecular diffusiv-ities in air and water should consult the text by Reed et al. (1987). 

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