Membrane permeation measurements

In permeation measurements the first signs of hydrogen diffusing through 1 mm steel membranes can be observed in a few minutes. The practical measurement of diffusion parameters tends to be rather unreproducibie. 

Water Permeation and Solute Separation through the Membrane. The measurements of water permeability of the 67 membranes prepared under different conditions were carried out by using an Amicon Diaflo Cell (effective membrane area, 13.9 cm2) under a pressure of 3 kg/cm2 at 25 °C. Some results are listed in Table 1067. It is apparent that much higher water absorption and permeability than the cellulosic membrane are characteristic of the 67 membranes prepared by both the casting polymerization and conventional casting. 

For gases, both permeation and diffusion data are best measured by permeation tests, many different types been described elsewhere. The same sheet membrane permeation test can quantify permeation coefficient Q, diffusion coefficient D, solubility coefficient s, and concentration c. The membrane, of known area and thickness, must be completely sealed to separate the high-pressure (initial) region from that containing the permeated gas it may need an open-grid support to withstand the pressure. The permeant must be suitably detected and quantified (e.g., by pressure or volume buildup, infrared (IR) spectroscopy, ultraviolet (UV), gas chromatography, etc.). 

Permeation measurements were conducted on the Pd and Pd-Ag/PSS membranes at elevated temperature (623 K to 873 K) and pressures (up to 1 MPa). Surfece morphology of the deposited layer was observed with a scanning electron microscope (SEM, S3(K)0N, HITACHI Co.) equipped with an energy dispersive spectrometer (EDS, HORIBA Co.). 

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.]. 

Membrane osmometry measurements were carried out with the capillary osmometer shown in Figure 3. Owing to the short equilibration time of the instrument and the low cut-off molar mass of the membrane, solute permeation through the membrane, which would show up as a drift of the baseline, did not cause problems even for the lowest molar mass fraction. M was obtained from... 

Passive diffusion through the lipid bilayer of the epithelium can be described using the partition coefficient between octanol/water (log P) and A log P (the difference between the partition into octanol/water and heptane/ethylene glycol or heptane/ octanol) [157, 158], The lipophilicity of the drug (log P) (or rather log D at a certain pH) can easily be either measured or calculated, and is therefore generally used as a predictor of drug permeability. Recently, a method using artificial membrane permeation (PAMPA) has also been found to describe the passive diffusion in a similar manner to the Caco-2 cell monolayers [159]. 

In the third part of the chapter the solid state properties of our block copolymer are examined. The surface energies of these materials are characterized by contact angle measurements. The organization of the polymer chains in the solid state phase is investigated by small-angle X-ray scattering (SAXS) and the gas selectivity of porous membranes coated with these block copolymers is characterized by some preliminary permeation measurements. 

Encouraged by the X-ray and contact angle results, we performed some preliminary gas-permeation measurements. Here, a self-supporting film is required and only the longer block copolymers were used. Fluoro-PSB-II and Fluoro-triblock were coated on porous Celgard 2400 membranes the measurements were taken at room temperature at a driving pressure of 5 bars. Since no absolute polymer layer thickness has been determined, only relative values of the permeability are given (Table 10.6). In the case of the separation of C02 from... 

Solubility and permeability were measured by a high throughput solubility assay and parallel artificial membrane permeation assay (PAMPA), respectively [56], The assays categorized 14 out of 18 drugs based on the BCS consistent with their known solubility and permeability characteristics [56],... 

HTS plates permit to determine drug permeability across a cell monolayer with a throughput similar to that of the parallel artificial membrane permeation assay (PAMPA), which measures rate of diffusion across a lipid layer.46 As is the case with PAMPA, the tiny surface area of the filters of the 96-well HTS presents an analytical challenge for compounds with low-to-moderate permeability. 

Another in vitro method for permeability screening was parallel artificial membrane permeation assay (PAMPA) initially reported by Kansy. In a PAMPA permeability screen, the Caco-2 cell mono-layer membrane is replaced by an artificially generated membrane. Versions of different artificial membranes that lack active transporter systems and pores have been developed to mimic the in vivo transcellular intestinal epithelial cell barrier. Therefore, the PAMPA screen only measures the intrinsic... 

Recently, there is some negativity towards PAMPA [52], seemingly due to an overexpectation and misunderstanding of PAM PA and the science of passive membrane permeation [53]. PAMPA is a refined descendant of log Poet and is an improved surrogate measurement for passive transcellular permeation. PAMPA permeability usually correlates well with passive transcellular permeation. It is important to correctly understand the pros and cons of this tool and to use it appropriately in drug discovery. 

Permeability of prodrugs will depend on the mechanism and (anatomical) site of conversion to the drug substance. When the prodrug-to-drug conversion is shown to occur predominantly after intestinal membrane permeation, the permeability of the prodrug should be measured. When this conversion occurs prior to intestinal permeation, the permeability of the drug should be detennined. Dissolution and... 

When the gas or vapor feed stream contains a component that is highly soluble in the polymer membrane and causes plasticization, then the selectivity as defined by Equation 4.6 will depend on the partial pressure or the amount of the plasticizing component sorbed into the membrane. Furthermore, pure-gas permeation measurements are generally not a good indicator of the separation performance, and mixed-gas permeation measurements will be needed [21-23]. Often, the mixed-gas selectivity is less than predicted from pure-gas measurements [8] however, the opposite has been observed [24], Competitive sorption effects can also compromise the prediction of mixed-gas behavior from pure-gas measurements [25], For gas pairs where each component is less condensable than C02, like 02/N2, it is generally safe to conclude that the selectivity characteristics can be accurately judged from pure-gas permeabilities at all reasonable pressures. When the gas pair involves a component more condensable than C02, plasticization is likely to be a factor and pure-gas data may not adequately reflect mixed-gas selectivity. When C02 is a component, the situation depends on the partial pressures and the nature of the polymer. 

The performance of a specific already produced membrane characterized by a defined (known or unknown) thickness depends on permeance, which can be evaluated by means of a permeation measurement. 

After preparation of newly developed membranes, high temperature permeation measurements were performed by VITO in Belgium. Steam treatment and membrane material characterisation were performed at SINTEF in Norway and reactor testing together with kinetic modelling of the reactor at IRC in France. The development of a high temperature test module for this reactor testing was the task of Velterop BV in the Netherlands. 

Since the relative concentration of residual adsorbed molecules at every level that can be identified by some physical measurement (from saturation to virtual dryness) is a linear function of as, it is reasonable to conclude that oq might indeed be a parameter of fundamental scientific value, potentially helpful in improving our understanding of phenomena that involve molecular association, e.g. chromatography, membrane permeation (Sect. 2.1), solubility and thermally induced gel-formation. 

---