Permeation data

AU that might be due to the influence of a strong magnetic field in which nitrogen and oxygen form aggregates [36] which carry more nitrogen, and spoil, in a sense, the separation process. 

Source Reprinted with permission from Journal of Membrane Science, On the air enrichment by polymer magnetic membranes by A. Rybak, Z. J. Grzywna and W. Kaszuwara, 336, 1-2, 79-85 Copyright (2009) Elsevier Ltd zico was obtained using a late time permeation curve according to Equation (9.23). Other methods mentioned above could be used only in the case of the sufficient amount of  

No Membrane B (mT) Measured oxygen content in permeate (%) Predicted (calculated) oxygen content in permeate (%) 

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Nevertheless, professional industrial hygienists are called upon routinely to select protective clothing that will provide an adequate, if not absolute, level of protection, even when permeation data are not available for a specific chemical/polymer combination. Their task is formidable. It is also a task that can be performed more easily with the assistance of an expert system. 

The program has been useful in searching and summarizing all of the polymers, with specific vendor models, that have published chemical permeation data on a chemical class basis. The advantage of this is the increased the probability of selecting polymers and/or vendors models that may exhibit equal or better chemical permeation resistance to similar chemicals that have not yet been tested. Thus, fewer models may have to be tested with untested chemicals to find an acceptable garment. 

It is noted that the time required for reaching the steady state of hydrogen diffusion is stress, specimen geometry, and dimension dependent, and cannot be used to compare with the permeation data as discussed earlier, which was measured from stress- and crack-free thin membrane specimens. 

Figure 7. Permeation data for a typical Fe-based MetGlass sample...

The rather time- and cost-expensive preparation of primary brain microvessel endothelial cells, as well as the limited number of experiments which can be performed with intact brain capillaries, has led to an attempt to predict the blood-brain barrier permeability of new chemical entities in silico. Artificial neural networks have been developed to predict the ratios of the steady-state concentrations of drugs in the brain to those of the blood from their structural parameters [117, 118]. A summary of the current efforts is given in Chap. 25. Quantitative structure-property relationship models based on in vivo blood-brain permeation data and systematic variable selection methods led to success rates of prediction of over 80% for barrier permeant and nonper-meant compounds, thus offering a tool for virtual screening of substances of interest [119]. 

Narayanan and Gunturi [33] developed QSPR models based on in vivo blood-brain permeation data of 88 diverse compounds, 324 descriptors, and a systematic variable selection method called Variable Selection and Modeling method based on the Prediction (VSMP). VSMP efficiently explored all... 

Au nanotubule membranes with the following approximate nanotubule diameters were used to obtain the majority of the data reported here i.d. = 28 1, 7.0 0.1, 1.9 0.1, and 1.5 0.2 nm. Figure 19 shows permeation data for transport of pyridine through these various membranes. Data for membranes derivatized with both the R = -C2H4-OH (upper solid curve) and the R = -C16H33 (lower dashed curve) thiols are shown. The corresponding flux data are shown in Table 3. As would be expected [114], the flux of pyridine decreases with decreasing tubule diameter for both the... 

FIG. 20. Toluene permeation data (membranes as per Fig. 19). In each case, the upper dashed line is for the R = -CieH, membrane and the lower solid line is for the R = -C2H4-OH membrane. 

Figure 3. Hydraulic permeation data jor PVA-water system (6)...

The numbers are the permeate concentrations divided by the bulk concentration. All the corrections to determine the degree of association are not yet known, but a decrease in this number is evidence of an increase in the degree of association. The solute is Indulin AT. The permeate data are obtained from the intercept of figures similar to Figure 4. 

The data were then treated with equation (2), and the cumulative amounts of drug released (0 were plotted against the square root of the time (t1/2) (Fig. 1). Excellent linearity was found, confirming that the release-permeation data followed the Higuchi model. 

TPX has a high selectivity for hydrogen gas permeation. Data of selected polymers are shown in Table 4.5. 

Eqs. (25) and (26) are, of course, identical when z = 1 and have been applied successfully to Dye I in two cases 81,82) (cf. Fig. 10). Eq. (26) has been applied with reasonable success to two divalent dyes80). Finally, Eq. (25) was tested against data for Dyes II and III. Some discrepancies between the experimental and calculated D(C) curves have been noted at the high concentration end82). No comparable anomalies are noticeable in the corresponding steady-state permeation data plotted in Fig. 9 (but it should be borne in mind that the high C region tends to be deemphasized in the latter type of plot). Further data are desirable. 

Some preliminary kinetic analyses of transient sorption and permeation data have been reported144,149. Examples from kinetic regimes where ideal kinetics is expected to be obeyed are shown in Fig. 17. The linearity of the relevant plots is satisfactory and the values of D3, D4 and D , Dd determined from these plots deviate from De in opposite directions, as expected l50-151 even though the detailed spatial dependence of S and DT in the membrane in question is two-dimensional145) (cf. previous subsection) and is, therefore, more complicated than envisaged in the theoretical... 

Transient sorption and permeation data may also be examined in the form of suitable moments. For example, in the case of sorption one may define the following moments171 ... 

Figure 2. Gel permeation data for polypeptide linear random coils plotted according to the method of Porath (8) M0,555 is plotted vs. Kd1/3. Lines drawn through the data from each column are lines of best fit determined by linear least-squares analysis. Numerical designation for each curve represents the agarose...

Figure 3. Gel permeation data for linear randomly coiled polypeptides on various agarose resins, plotted according to the method of Ackers (9). M0 555 is plotted vs. the inverse error function complement of Kd (erfc 1 Kd). Lines drawn through the data points represent best fits obtained from linear least-squares analysis of the data. Numerical designation of each curve represents the percent agarose composition for the resin used. Filled triangles on the curve for the 6% resin, and the filled squares on the curve for the 10% resin are points determined using fluorescent proteins. Data for the labeled polypeptides were not included in the least-squares analysis.

The concept of unrelaxed volume in glassy polymers is used to interpret sorption and transport data for pure and mixed penetrants A review of recent sorption and permeation data for mixed penetrants indicates that competition for sorption sites associated with unrelaxed gaps between chain segments is a general feature of gas/glassy polymer systems This observation provides convincing support for the use of the Langmuir isotherm to describe deviations from simple Henry s law sorption behavior. 

Whereas the dual sorption and transport model described above unifies independent dilatometric, sorption and transport experiments characterizing the glassy state, an alternate model offered recently by Raucher and Sefcik provides an empirical and fundamentally contradictory fit of sorption, diffusion and single component permeation data in terms of parameters with ambiguous physical meanings (28), The detailed exposition of the dual mode model and the demonstration of the physical significance and consistency of the various equilibrium and transport parameters in the model in the present paper provide a back drop for several brief comments presented in the Appendix regarding the model of Raucher and Sefcik,... 

Figure 3. Time lag for diffusion of CO at 35 °C in a U.9 mil thick polycarbonate film conditioned by prior exposure to C02 The data are from Ref. 15. Calculated time lags based on the matrix model (solid line) and the dual-mode model (broken line) use parameters determined from fitting the sorption and permeation data.

As a general rule, membrane material changes affect the diffusion coefficient of a permeant much more than the sorption coefficient. For example, Figure 2.18 shows some typical gas permeation data taken from a paper of Tanaka et al. [23], The diffusion and sorption coefficients of four gases in a family of 18 related polyimides are plotted against each other. Both sorption and diffusion coefficients... 

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...

Figure 7.8 C3H6/C3Hg experimental upper bound based on pure gas permeation data over the range 1-4 atm feed pressure.

Very recently, new descriptors have successfully been derived from 3-D molecular fields. These descriptors were correlated with the experimental permeation data by discriminant partial least-squares methods. The training set consisted of 44 compounds. The authors were able to deduce a simple mathematical model that allows external prediction. More than 90% of blood-brain permeation data were correctly predicted [77]. 

The literature references sodium caprate (CIO) being used as a permeation enhancer in both preclinical (Ishizawa et al. 1987) and clinical studies of Class III compounds (Lindmark et al. 1997). Permeation data from in situ rodent studies calculate tight junctions opening after CIO dosing which is consistent with the cross-sectional diameter of ASOs (Ma et al. 1992 Tsutsumi et al. 2003). The work of Raoof et al. demonstrated in the pig and dog, that the use of permeation enhancers, notably CIO, represents an attractive strategy to enhance the oral delivery of ASO molecules (Raoof et al. 2002, 2004). In Fig. 12.3 the pharmacokinetic of an orally administered ASO utilizing sodium caprate as permeation enhancer is illustrated. 

Despite the fact that the skin is a heterogeneous membrane, Fick s laws of diffusion have been successfully used to analyze skin permeation data. Solutions to the second law have been used in mechanistic interpretations (see later) and in considering concentration profiles within the skin. Fick s first law has been used to analyze steady-state diffusion rates and in the development of predictive models for skin permeability. 

The general features of the D vs. Cj relations for amorphous polymer-solvent systems slightly above or below Tg° are not fully elucidated. This is mainly due to the fact that, as will be explained in the next section, the sorption processes in glassy polymers are not Fickian and hence the methods for the determination of D (cj) presented in the previous section can no longer be applied. In principle, D values of such systems could be determined from steady-state permeation measurements, but Kishimoto (unpublished) has shown that the analysis of permeation data on glassy systems is complicated by factors which are not yet fully resolved. 

From what we have discussed in (b"), it follows that when the two sets of D(Cj) data derived from sorption experiments and permeation experiments do not agree with one another within the expected limits of accuracy, the sorption values of D are incorrect and the measured sorption processes are non-Fickian. This method of examining whether sorption is Fickian or not is particularly useful when the experimental sorption curve has a shape equivalent to the true Fickian curve. Meares (1958a) demonstrated that the D values for the system polyvinyl acetate-allyl chloride at 40° C. determined from steady-state permeation data in-... 

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