Permeation curves early-time

In the early potentiostatic experiments by Devanathan and Stachurski [98], the time required for the subsurface concentration to become constant, as assumed, was treated simply as a shift in the timescale at the beginning of a permeation curve. However, the permeation behavior for the constant concentration case and that in which the... 

Figure 9.8 An example of early-time permeation curve according to Equation (9.22). Reprinted with permission from journal of Membrane Science, On the air enrichment by polymer magnetic membranes by A. Rybak, Z. j. Crzywna and W. Kaszuwara, 336, 1-2, 79-85, Copyright (2009) Elsevier Ltd...

We define this permeability as apparent, to emphasize that there are important but hidden assumptions made in its derivation. This equation is popularly (if not nearly exclusively) used in culture cell in vitro models, such as Caco-2. The sink condition is maintained by periodically moving a detachable donor well to successive acceptor wells over time. At the end of the total permeation time f, the mass of solute is determined in each of the acceptor wells, and the mole sum mA (t) is used in Eq. (7.10). Another variant of this analysis is based on evaluating the slope in the early part of the appearance curve (e.g., solid curves in Fig. 7.14) ... 

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