Membrane Permeation Experiments

All parameters used in equations (1) and (2) were calculated from single gas adsorption and membrane permeation experiment. The numerical method for solving above equations were MOL(Method Of Line). These calculations were executed using LSODE solver(FORTRAN code). 

With the aim to develop a drug delivery system with thermal stimuli respons-ing, Nozawa et al. have been investigated liquid crystal (LC)-entrapped membranes, polymer alloyed membranes and LC-adsorbed membranes for the transport and release of indomethacin. Polymer alloyed membranes were obtained by polymerizing aaylic monomers in presence of LC and LC-adsorbed membrane were obtained by adsorbing LC into porous hydrophobic polymer membrane. Permeation experiments showed that below and above the gel-liquid crystal phase transition tanperature of the LC, the extent of thermo-sensitivity for LC-adsorbed... 

Returning to Eq. (21), direct evaluation of is difficult due to cj,/ , the solute concentration at the membrane retentate surface. In principle, c, /g could be experimentally determined by using feed solutions of high solute concentration so that b/s — b/0- However, solutions with high solute concentrations have physical properties which make data from membrane permeation experiments difficult to collect and evaluate, i.e., high viscosities, solute—solute (activity coefficient) interactions, aggregate formation, etc. Instead, a graphical mediod is preferable after modification of Eq. (21). 

In a permeation experiment, an HERO module with a membrane area of 200 m is used to remove a nickel salt from an electroplating wastewater. TTie feed to the module has a flowrate of 5 x IQ— m /s, a nickel-salt composition of 4,(X)0 ppm and an osmotic pressure of 2.5 atm. The average pressure difference across the membrane is 28 atm. The permeate is collected at atmospheric pressure. The results of the experiment indicate that the water recovery is 80% while the solute rejection is 95%. Evaluate the transport parameters Ay and (D2u/KS). 

The evaluation of the apparent ionization constants (i) can indicate in partition experiments the extent to which a charged form of the drug partitions into the octanol or liposome bilayer domains, (ii) can indicate in solubility measurements, the presence of aggregates in saturated solutions and whether the aggregates are ionized or neutral and the extent to which salts of dmgs form, and (iii) can indicate in permeability measurements, whether the aqueous boundary layer adjacent to the membrane barrier, Umits the transport of drugs across artificial phospholipid membranes [parallel artificial membrane permeation assay (PAMPA)] or across monolayers of cultured cells [Caco-2, Madin-Darby canine kidney (MDCK), etc.]. 

Various membrane types suitable for permeation experiments are listed below. More details are available in literature [66],... 

Reconstructed Human Epidermis Equivalents Because of the limited availability of human skin, reconstructed human epidermis equivalents are under investigation to serve as membranes in permeation experiments. A summary on these replacement tools has been recently published by Netzlaff et al. [92], First results of a German prevalidation study have shown the suitability of such bioengineered human epidermis equivalents in permeation studies [93],... 

The successful application of in vitro models of intestinal drug absorption depends on the ability of the in vitro model to mimic the relevant characteristics of the in vivo biological barrier. Most compounds are absorbed by passive transcellular diffusion. To undergo tran-scellular transport a molecule must cross the lipid bilayer of the apical and basolateral cell membranes. In recent years, there has been a widespread acceptance of a technique, artificial membrane permeation assay (PAMPA), to estimate intestinal permeability.117118 The principle of the PAMPA is that, diffusion across a lipid layer, mimics transepithelial permeation. Experiments are conducted by applying a drug solution on top of a lipid layer covering a filter that separates top (donor) and bottom (receiver) chambers. The rate of drug appearance in the bottom wells should reflect the diffusion across the lipid layer, and by extrapolation, across the epithelial cell layer. 

Results of such single-molecule permeation experiments, using the MV +/ Ru(bpy)3 pair (Fig. 16), and membranes with four different nanotubule i.d.s, are shown in Fig. 17. The slopes of these permeation curves define the fluxes of and Ru(bpy)3 across the membrane. A permeation selectivity coefficient (ai)t can be obtained by dividing the flux by the Ru(bpy)3 flux. 

The smallest i.d. nanotubule membrane (Fig. 17D) showed a measurable flux for MV +, but the larger Ru(bpy)3 could not be detected in the permeate solution, even after a 2-week permeation experiment. 

A). To demonstrate this point, the rate and selectivity of transport across a conventional (Fig. 15A) and a bottleneck membrane were compared. Both membranes were able to cleanly separate from Ru(bpy)3 in the two-molecule permeation experiment (see below). Hence, these membranes showed comparable, excellent selectivity. However, as expected, the flux of across the bottleneck nanotubule membrane was dramatically higher than for the conventional nanotubule membrane (14 vs. 0.07 nmol hr cm ). 

Figure 18B shows the absorption spectrum for the feed solution used in the permeation experiment. Although both molecules are present in solution at the same concentration, the higher absorbance of the quinine nearly swamps out the 252-nm peak of the pyridine. Figure 18C shows the absorption spectrum of the permeate solution after a 72-hour permeation experiment. In spite of the higher absorbance of the quinine (larger molecule), only the peak for the pyridine (smaller molecule) is seen in this spectrum. Note, in particular, the complete absence of the very intense quinine band centered at 225 nm. Figure 18C shows that, to our ability to make the measurement, this bottleneck nanotubule membrane has filtered these two molecules on the basis of molecular size. 

The mechanism of diffusion of these permeant molecules in these membranes is an issue that must be explored in detail. We have shown [71] that the R = -C2H4-OH-derivatized nanotubules flood when immersed in water. In contrast, permeation experiments with inorganic salts suggest that the R = -C16H33 nanotubules do not flood with water. Hence, in these membranes the permeate molecule is partitioned into and diffuses through the Cig phase within the tubes. 

Physicochemical tools can be categorized into two types membrane binding experiments and permeation experiments (Figure 6.4) [3]. The permeation barrier of a phospholipid bilayer is heterogeneous in nature and the rate-limiting barrier... 

The composite membrane was subjected to the permeation experiments in which the volume flux of water and the rejection of polymer solutes, defined by... 

Figure 24 shows the rejections of polymer solutes, polyethylene glycols) (PEG) with monodispersed molecular weights. From Fig. 24, it is apparent that the composite membrane can find application for ultrafiltration. The molecular weight cut-off drastically decreased by more than 10 fold from the swollen state at 25 °C to the shrunken state at 45 °C. Thus the switching ability of the gel was demonstrated in the permeation experiments. 

Fig. 23. Swelling ratios of NIPA gel and volume fluxes across the composite membrane at various temperatures. Pressure difference between permeate and feed solutions in the permeation experiments is 10 [kg cm-2]...

Finally, we described the permeation characteristics of a thermosensitive gel supported on porous glass. The switch functional ability of the membrane was demonstrated in permeation experiments. It was pointed out that the change in the permeation characteristics resulted from that in the pore structure in the gel. 

Typical data for the application of this method are shown in Fig. 16. They refer to standard permeation experiments in which the upstream (at X = 0) and downstream (at X = 1) surfaces of the membrane are maintained at constant penetrant activities... 

The presence of the term y) makes the permeability coefficient a function of the solvent used as the liquid phase. Some experimental data illustrating this effect are shown in Figure 2.7 [11], which is a plot of the product of the progesterone flux and the membrane thickness, 7, against the concentration difference across the membrane, (cio — cif ). From Equation (2.28), the slope of this line is the permeability, P]. Three sets of dialysis permeation experiments are reported, in which the solvent used to dissolve the progesterone is water, silicone oil and poly(ethylene glycol) MW 600 (PEG 600), respectively. The permeability calculated from these plots varies from 9.5 x 10 7 cm2/s for water to 6.5 x 10 10 cm2/s for PEG 600. This difference reflects the activity term yj/ in Equation (2.28). However, when the driving force across the membrane is... 

Figure 2.40 Blocking of hydrogen in hydrogen/sulfur dioxide gas mixture permeation experiments with finely microporous membranes [63] as a function of the amount of sulfur dioxide adsorbed by the membrane. As sulfur dioxide sorption increases the hydrogen permeability is reduced until at about 140 cm3 (SO2) (STP) /g, the membrane is completely blocked and only sulfur dioxide permeates. Data obtained at several temperatures fall on the same master curve ( , 0°C A. —10 °C , — 20.7 °C A, —33.6°C). Reprinted from R. Ash, R.M. Barrer and C.G. Pope, Flow of Adsorbable Gases and Vapours in Microporous Medium, Proc. R. Soc. London, Ser. A, 271, 19 (1963) with permission from The Royal Society...

In the discussion of concentration polarization to this point, the assumption is made that the volume flux through the membrane is large, so the concentration on the permeate side of the membrane is determined by the ratio of the component fluxes. This assumption is almost always true for liquid separation processes, such as ultrafiltration or reverse osmosis, but must be modified in a few gas separation and pervaporation processes. In these processes, a lateral flow of gas is sometimes used to change the composition of the gas on the permeate side of the membrane. Figure 4.14 illustrates a laboratory gas permeation experiment using this effect. As the pressurized feed gas mixture is passed over the membrane surface, certain components permeate the membrane. On the permeate side of the membrane, a lateral flow of helium or other inert gas sweeps the permeate from the membrane surface. In the absence of the sweep gas, the composition of the gas mixture on the permeate side of the membrane is determined by the flow of components from the feed. If a large flow of sweep gas is used, the partial... 

The mean free path, /, of the C02 molecules at the temperatures and pressures of the permeation experiment are by far smaller than the membrane pore size, d, that is, d, /.. Then, Knudsen flow is not possible since the determining process is gaseous laminar flow through the membrane pores [18]. It is therefore feasible to apply Darcy s law for gaseous laminar flow (Equations 10.19 through 10.23). 

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