Experimental procedure permeability measurements

We have developed an vitro experimental procedure to measure the permeation characteristics of drugs through skin (7). The first drug to pass through the development activity is scopolamine, which is a belladonna alkaloid with a pK of 7.35. For scopolamine, skin permeability is strongly pH dependent, in that the nonionic (more lipophilic) form... 

The experimental procedure and method of treatment of compression-permeability data have been explained by Grace [Chem. Eng. Prog., 49, 303, 427 (1953)], who showed that the values of a measured in such a cell and in a pressure filter were the same, and by Tiller [Filtr Sep., 12, 386 (1975)]. 

In this section the laboratory measurements of CC -foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown in the order of the effects of surfactant concentration, CC -foam fraction, and rock permeability. The preparation of the surfactant solution is briefly mentioned in the Effect of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfactant Enordet X2001 (AEGS) from Shell were used for this experimental study. 

For some compounds in the Wilschut database more than one permeability coefficient was gathered from literature. In some cases, the differences in kp were greater than one log unit underlining the interlaboratory variations of such measurements. For the development of a new QSPR model one may now either choose one representative data point for each molecule or combine the multiple data points in a reasonable way. In some cases authors even employed all the available data for a single compound. Apart from the permeability data, the data on the partition coefficient and even on the molecular weight may vary from one report to another. Differences in the partition coefficient are easily explained Some collections list experimentally determined values which depend on the experimental procedure employed... 

Similar approaches are used for most steady-state measurement techniques developed for mixed ionic-electronic conductors (see -> conductors and -> conducting solids). These include the measurements of concentration-cell - electromotive force, experiments with ion- or electron-blocking electrodes, determination of - electrolytic permeability, and various combined techniques [ii-vii]. In all cases, the results may be affected by electrode polarization this influence should be avoided optimizing experimental procedures and/or taken into account via appropriate modeling. See also -> Wagner equation, -> Hebb-Wagner method, and -> ambipolar conductivity. 

We describe the high pressure triaxial cell in which tests will be performed. Then we present the strain local measurements developed to identify and characterize the different mechanical stages that can be correlated to permeability evolution and in particular strain localization. The experimental procedure focused for materials having low permeability and hydromechanical coupling (i.e. effective stress has an important role) is described. Finally we present two materials involved in the SELFRAC project and with which we have to improve our experimental developments. 

An experimental set up (high pressure triaxial cell and local strain measurement system) and an experimental procedure have been developed in order to quantify the permeability evolution with deviatoric stress on clays of very low permeability. Developed techniques have been improved on concrete and sandstone. We are able to detect with precision strain localization and we are able to measure with the pulse method, permeability, at different stages of loading. A testing program on both Boom Clay and Opalinus is in progress. 

Experimental Procedure. Mixed gas transport through a 30jim QPAC-25 film was monitored for a total of seven days using a pressure gradient of 64.7 psia and a temj rature of 35.0 C. As the permeate volume was collected, total system permeability was measured by recording permeate pressure increase with time. After 2 to 10 torr of gas was collected as permeate, the feed pressure was released. Valve B, as shown in Figure 2, was closed, and valve A was opened. 

The information about various properties of microporous materials (especially their adsorption-desorption, permeability, adhesion and mechanical stability characteristics) in the scientific literature is very abundant but still eventual. The ordinary procedure of the study of microporous materials comprises their penetration by such or such method, measurement of some characteristics (for instance, adsorption isotherms) and, sometimes, computer treatment of experimental results. However, it is obvious that the unification of experimental data on various characteristics of such materials in the light of the conditions of their formation and resulting structure could allow not only systematization of the related information but also minimization of the number and the cost of experiments. 

Acquire Basic Data. Because of the novelty of membrane-based gas separations, a scarcity of important design data often b encoitntered. Some tabulations do exist. Cor exat e. Table 20.1-1 and T es 20.4-1 and 20.4-2, which are discussed later. In addition, membrane manufacturers can be of help for common systems. If one b considering unusual systems or novel membranes, some experimental determination of permeabilities is likely to be necessary. Procedures and equipment for such measurements are described in later sections. 

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