Membrane permeation technique

Ono, N. Hirayama, F. Arima, H. Uekama, K. Determination of stability constant of P-cyclodextrin complexes using the membrane permeation technique and the permeation behavior of drug-competing agent-P-cyclodextrin ternary systems. Eur. J. Pharm. Sci. 1999, 8 (2), 133-139. 

The absorption/desorption method is more involved experimentally compared to the membrane permeation technique, since the protein must be incorporated into the hydrogel, but not adsorbed, and subsequently dried. The dissolution study is typically carried out in USP no. 2 apparatus, with media continuously being monitored by UV analysis. Penetration of the dissolution media into the dehydrated polymer complicates the diffusion process, commonly producing a lag time prior to protein release. 

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). 

While in vivo studies assess absorption rates as process-lumped time constants from blood level versus time data, these rate parameters encompass the kinetics of dosage-form release, GI transit, metabolism, and membrane permeation. The use of isolated tissue and cellular preparations to screen for drug absorption potential and to evaluate absorption rate limits at the tissue and cellular levels has been expanded by the pharmaceutical industry over the past several years. For more detail in this regard, the reader is referred to an article by Stewart et al. [68] for references on these preparations and for additional details on the various experimental techniques outlined below. 

The permeation technique is another commonly employed method for determining the mutual diffusion coefficient of a polymer-penetrant system. This technique involves a diffusion apparatus with the polymer membrane placed between two chambers. At time zero, the reservoir chamber is filled with the penetrant at a constant activity while the receptor chamber is maintained at zero activity. Therefore, the upstream surface of the polymer membrane is maintained at a concentration of c f. It is noted that c f is the concentration within the polymer surface layer, and this concentration can be related to the bulk concentration or vapor pressure through a partition coefficient or solubility constant. The amount... 

Evapomeation is a new membrane-separation technique for liquids mixtures, which eliminates some disadvantages of the pervaporation technique such as the decreasing of membrane permselectivity, due to its swelling by the direct contact with the feed solution. In evapomeation technique the membrane is not in direct contact with the feed solution, only with the solution s vapors. In this way the swelling of the membrane could be suppressed and consequently, the permeation rates in evapomeation are smaller than those in pervaporation, but the separation factor is greater [83],... 

G. L. Flynn, H. Durrheim, and W. I. Higuchi. Permeation of hairless mouse skin II Membrane sectioning techniques and influence on alkanol permeabihties. J. Pharm. Sci. 70 52-56 (1981). 

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. 

It has recently been demonstrated that solutes can be extracted from ionic liquids by perevaporation. This technique is based on the preferential partitioning of the solute from a liquid feed into a dense, non-porous membrane. The ionic liquids do not permeate the membrane. This technique can be applied to the recovery of volatile solutes from temperature-sensitive reactions such as bioconversions carried out in ionic liquids (34). 

Table 1.1 shows two developing industrial membrane separation processes gas separation with polymer membranes (Chapter 8) and pervaporation (Chapter 9). Gas separation with membranes is the more advanced of the two techniques at least 20 companies worldwide offer industrial, membrane-based gas separation systems for a variety of applications. Only a handful of companies currently offer industrial pervaporation systems. In gas separation, a gas mixture at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the feed mixture the membrane permeate is enriched in this species. The basic process is illustrated in Figure 1.4. Major current applications... 

A number of membrane materials and membrane preparation techniques have been used to make reverse osmosis membranes. The target of much of the early work was seawater desalination (approximately 3.5 wt% salt), which requires membranes with salt rejections of greater than 99.3 % to produce an acceptable permeate containing less than 500 ppm salt. Early membranes could only meet... 

In an attempt to overcome the significant difficulties that the presence of water vapor poses to the analysis of very volatile compounds, purge-and-membrane extraction techniques have been developed that largely prevent the introduction of water into the analytical system. Typical implementations of this form of sample introduction have been called by its developers membrane extraction with a sorbent interface (MESI),97 or membrane introduction mass spectrometry (MIMS).98 " They are based on a silicone hollow-fiber membrane that is inserted into the sample to be monitored, and the passing of a certain volume of inert gas through the membrane. Volatile compounds permeate the membrane and are swept to the adsorbent trap from which they are desorbed into the GC. This method of sample introduction is particularly suited for field and process monitoring and for dirty samples, since it prevents any nonvolatile compounds from entering the analytical system.100... 

The permeation technique as discussed in the context of permeation membranes in Section II.2, can also be used to determine diffusion coefficients and minority conductivities (in fact steady-state oxygen flux that is given by (see Eq. (34))... 

Enrichment consists of a significant increase in the concentration of one or several species in the desired stream, although by this operation neither high recovery nor purity is achieved. Condensation, physical absorption, membrane permeation, cryogenic distillation, and adsorption are convenient separation techniques. 

The second technique for C02/methane separation is membrane permeation, now standard in industry. Cryogenic distillation may be applied for methane-enrichment purposes with some technical precautions because of C02 freezing. Equilibrium adsorption on activated carbon would give poor separation. Molecular sieving would permit only the removal of oxygen and nitrogen. 

In all types of membrane extraction, the membrane separates the sample phase (often called donor or feed solution) from the acceptor or strip phase and the analyte molecules pass through the membrane from the donor to the acceptor. This process is often called pertraction (permeation-extraction). The membrane extraction techniques can be divided into porous and nonporous membrane techniques. Another distinction is between one-, two-, or three-phase membrane extraction techniques. 

Both retentate and permeate from membrane separation techniques have become important starting materials in producing novel products and ingredients from milk of unique functional properties and organoleptic quality. Henning et al. [7] enumerated the current and new applications of membrane technologies in the dairy industry, which include... 

ORD-CD ], potentiometry, microcalorimetry, surface tension, membrane permeation, electro-phoresis, and freezing point depression. Chromatographic methods include HPLC, paper, and TLC techniques. 

Geus et al. [75] reports diffusion data at 21 and 145°C for Hj, N2, CH4, CO2 and CF2CI2 in silicalite membranes on a clay support which are obtained with the similar transient permeation technique as used above by Vroon. The diffusion coefficients for methane are about two orders of magnitude smaller than those obtained by PF-NMR methods. Usually this last technique gives relatively large diffusion coefficient values, which in the case of n-butane are of the same order of magnitude as reported for FR techniques and membrane techniques as reported by Kapteyn. 

The conclusion so far must be that synthesis and sample preparation techniques play an important role. Diffusion data to be used in permeation experiments should be measured on membranes with techniques which reflect as closely as possible the transport phenomena during permeation. This also minimises heat effects due to adsorption/desorption which play an important role in diffusion experiments based on large crystals, but is of minor importance in membrane experiments [101]. 

Roughness (placing protuberance or corrugation on the surface) These techniques are difficult to scale-up to intermediate or large size modules and are often limited by their high axial pressure drop. The approach, however, does demonstrate that shear stresses developed by flow instabilities enhance membrane permeation rates for difficult feeds. ... 

These developments result from the introduction of composite membranes, originally developed in the 1970s primarily, for desalination by reverse osmosis. Application of the same membrane fabrication techniques to pervaporation membranes radically improved their performance and spurred commercial utilization. Today, pervaporation and vapor permeation plants are widely used to dehydrate volatile organics and separate other mixtures, primarily in the pharmaceutical and fine chemical industries. 

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