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Charged species transport

The Case for Charged-Species Transport from Cellular and Liposomal Models... [Pg.218]

Although the basic principles of type III potentiometric sensors are apphcable for gaseous oxide detection, this should not obscure the fact that these sensors still require further development. This is especially true in view of the kinetics of equilibria and charged species transport across the solid electrolyte/electrode interfaces where auxiliary phases exist. Real life situations have shown that, in practice, gas sensors rarely work under ideal equilibrium conditions. The transient response of a sensor, after a change in the measured gas partial pressure, is in essence a non-equilibrium process at the working electrode. Consequently, although this kind of sensor has been studied for almost 20 years, practical problems still exist and prevent its commercialization. These problems include slow response, lack of sensitivity at low concentrations, and lack of long-term stability. " It has been reported " that the auxiliary phases were the main cause for sensor drift, and that preparation techniques for electrodes with auxiliary phases were very important to sensor performance. ... [Pg.120]

Griffiths, S.K. and Nilson, R.H., Charged species transport, separation, and dispersion in nanoscale channels Autogenous electric field-flow fractionation. AnaZ. Chem., 2006, 78 8134—8141. [Pg.1117]

Of all the techniques, it is those of Group 1 that are likely to give the most realistic data, simply because they measure transport of charged species only. They are not the easiest experimental techniques to perform on polymeric systems and this probably explains why so few studies have been undertaken. The experimental difficulties associated with the Tubandt-Hittorf method are in maintaining nonadherent thin-film compartments. One way is to use crosslinked films [79], while an alternative has been to use a redesigned Hittorf cell [80]. Although very succesful experimentally, the latter has analytical problems. Likewise, emf measurements can be performed with relative ease [81, 82] it is the necessary determination of activity coefficients that is difficult. [Pg.511]

In the transport across a phospholipid bilayer by passive diffusion, the permeability of the neutral form of a molecule is 10X times greater than that of the charged form. For the epithelium, the discrimination factor is 105. The basement membrane (Fig. 2.5) allows passage of uncharged molecules more readily than charged species by a factor of 10 [76]. [Pg.17]

Palm et al. [578] derived a two-way flux equation which is equivalent to Eq. (7.13), and applied it to the permeability assessment of alfentanil and cimeti-dine, two drugs that may be transported by passive diffusion, in part, as charged species. We will discuss this apparent violation of the pH partition hypothesis (Section 7.7.7.1). [Pg.142]

The transport of charged species across a membrane requires an additional term to be added to Equation 9.1 to allow for the electric field ... [Pg.269]

Ambipolar diffusion involves the transport of charged species, and in such cases overall electric charge neutrality must be maintained during diffusion. Moreover, during ambipolar diffusion the difference in the mobilities of the diffusing species sets up a field, the Nernst field, that influences the rates of motion of the particles. [Pg.241]

As suggested before, the role of the interphasial double layer is insignificant in many transport processes that are involved with the supply of components from the bulk of the medium towards the biosurface. The thickness of the electric double layer is so small compared with that of the diffusion layer 8 that the very local deformation of the concentration profiles does not really alter the flux. Hence, in most analyses of diffusive mass transport one does not find any electric double layer terms. For the kinetics of the interphasial processes, this is completely different. Rate constants for chemical reactions or permeation steps are usually heavily dependent on the local conditions. Like in electrochemical processes, two elements are of great importance the local electric field which affects rates of transfer of charged species (the actual potential comes into play in the case of redox reactions), and the local activities... [Pg.121]


See other pages where Charged species transport is mentioned: [Pg.218]    [Pg.80]    [Pg.405]    [Pg.168]    [Pg.117]    [Pg.639]    [Pg.288]    [Pg.3]    [Pg.218]    [Pg.80]    [Pg.405]    [Pg.168]    [Pg.117]    [Pg.639]    [Pg.288]    [Pg.3]    [Pg.206]    [Pg.350]    [Pg.475]    [Pg.529]    [Pg.559]    [Pg.136]    [Pg.543]    [Pg.53]    [Pg.168]    [Pg.215]    [Pg.127]    [Pg.260]    [Pg.296]    [Pg.305]    [Pg.346]    [Pg.230]    [Pg.279]    [Pg.29]    [Pg.6]    [Pg.117]    [Pg.207]    [Pg.670]    [Pg.504]    [Pg.548]    [Pg.342]    [Pg.30]    [Pg.170]   


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