Solute reflection coefficient

Transport Properties. Important transmembrane transport parameters of the fibers are Lp, the hydraulic conductivity Pm, the diffusive permeability for a given solute o, the solute reflection coefficient and R, the solute rejection. These coefficients appear in the following equations, which are assumed to be valid at the steady state at each position Z along the fiber wall ... 

Solute reflection coefficients change markedly when solute size approaches the average pore size of the membrane. 

Note Here Cj, tt and P correspond to infinitely thin solutions in equilibrium with the local section of the membrane therefore C, is the molar concentration of solute i in a solution of osmotic pressure w.) There are three parameters here Qjj (the intrinsic hydraulic permeability), P (the local solute permeahility coefficient) and <7,- (the local solute reflection coefficient). When these two equations are integrated across a membrane of thickness assuming Qsi, P and <7 to be essentially constant across the membrane thickness, one obtains, for the whole membrane, two equations for the Spiegler-Kedem model (based on the Kedem-Katchalsky model) ... 

That the rate profiles are close to parallel shows that the variations in rates reflect the changing concentration of nitronium ions, rather than idiosyncrasies in the behaviour of the activity coefficients of the aromatic compounds. The acidity-dependences of the activity coefficients of / -nitrotoluene, o- and -chloronitrobenzene (fig. 2.2, 2.3.2), are fairly shallow in concentrations up to about 75 %, and seem to be parallel. In more concentrated solutions the coefficients change more rapidly and it... 

The pressure difference between the high and low pressure sides of the membrane is denoted as AP the osmotic pressure difference across the membrane is defined as Att the net driving force for water transport across the membrane is AP — (tAtt, where O is the Staverman reflection coefficient and a = 1 means 100% solute rejection. The standardized terminology recommended for use to describe pressure-driven membrane processes, including that for reverse osmosis, has been reviewed (24). 

The simplest osmotic dosage form, ALZA Corporation s OROS elementary osmotic pump (Fig. 7), combines the dmg and sometimes an osmotic agent in a monolithic core and deflvers the dmg in solution (102). The mass dehvery rate with time dm df) of the dmg solution is described by equation 4, where is the hydrauHc permeabiUty of the membrane, a is the membrane reflection coefficient, Atz is the osmotic pressure gradient, APis the hydrostatic back pressure, A is the area of the membrane, C is the dissolved concentration of the dmg, and b is the membrane thickness. 

Here the permeability of the membrane to the solute is defined in terms of reflection coefficients aQ and for osmosis and filtration respectively. When (To = 1, then perfect semi-permeabihty results. in Eq. (4) is the diffusive permeabihty of the membrane, while (Cj) is the average composition of the solute in the membrane. 

The influence of an interfacial kinetic barrier on the transfer process is readily illustrated by fixing the concentrations and the diffusion coefficients of Red for the two phases and examining the current response of the UME as K is varied. For illustrative purposes, we arbitrarily set and y = 1, i.e., initially the equilibrium conditions are such that there are equal concentrations of the target solute in the two phases, and the solute diffusion coefficient is phase-independent. Figure 17 shows the chronoamperometric characteristics for several K values from zero up to 1000. Under the defined conditions, these values of K reflect the ease with which the transfer process can respond to a perturbation of the local concentration of Red in phase 1, due to electrolytic depletion. 

The transport of both solute and solvent can be described by an alternative approach that is based on the laws of irreversible thermodynamics. The fundamental concepts and equations for biological systems were described by Kedem and Katchalsky [6] and those for artificial membranes by Ginsburg and Katchal-sky [7], In this approach the transport process is defined in terms of three phenomenological coefficients, namely, the filtration coefficient LP, the reflection coefficient o, and the solute permeability coefficient to. 

TABLE 1. Biophysical characteristics of human fetal liver CD34 CD38 cells. Legends Vo - cell volume in isoosmotic solutions, Vb - osmotically inactive volume, Lp - permeability coefficient of membranes for water, p - permeability coefficient of membranes for DMSO cryoprotectant, a - reflection coefficient. 

I. 46. The magnitude of the coefficient reflects the electric charge distribution of the ionic species. A 0.1 molal solution of Al2(S04)3 has an activity coefficient of only 0.035. It should also be noted that, in dilute solutions, activity coefficients of electrolytes decrease in magnitude with increasing concentration. A minimum is reached and the coefficient then increases with concentration. See Activity Debye-Huckel Law Biomineralization... 

The reflection coefficient ( a ) was estimated by allowing leaf tissue to equilibrate first in distilled water, then in a O.U M mannitol solution for two hr and finally in a distilled water solution overnight. The difference in weight between the initial distilled water equilibration and final distilled water equilibration was assumed to be an estimate of internal solute leakage and, therefore, a direct estimate of a. The data in Table V shows that loss of solute by the tissue is significant after ozone fumigation and verifies the predicted decrease in the reflection coefficient. 

It is rather difficult to rationalize a decreased membrane permeability to water (Lp) because of oxidant exposure. We suspect, therefore, that the apparent decreased water permeability results in fact from a decreased reflection coefficient leading to solute loss and hence an apparent lower water transport rate. In any case, these data clearly demonstrate the occurrence of oxidant-induced alterations in membrane properties. 

The apparent reflection coefficient (=(C5g - C pf/C, centration of solute in the permeate) may depend on the filtrate flux, when the real reflection coefficient cr is constant. Explain the possible reason for this. 

Experimentally, / and a have been poorly quantified (Levick, 1994 McGuire and Yuan, 2001 Parameswaran et al., 1999). Retardation and reflection coefficients may depend on flow rate, solute and tissue properties. 

Here An = RT cosm, Lp = permeability for solute (cm s 1), AP = hydrostatic pressure difference, An = osmotic pressure, a = reflection coefficient, Acs = solute concentration difference, and cs = average solute concentration in upstream solution. Membranes with a reflection coefficient cj —> 0 are permeable to all components whereas a membrane with <7—> 1 rejects all solutes. 

Figure l(ii) shows experimental results obtained when a membrane of compacted clay separates salt solutions initially at 3 M and 0.5 M. The salt reflection coefficient 1 — A transient pressures are observed the curves in fig. l(ii) are best fits to the form (10a). From the two rate constants and magnitude of the pressure we may estimate the three transport coefficients in (4). 

In general, the flow of water due to a chemical potential gradient is called chemical osmosis. When compacted, clay can act as a semi-permeable membrane due to overlapping diffuse double layers. This means that the movement of solute particles is restricted across the membrane, while solvent is free to flow. To attain chemical equilibrium in case of an initial concentration gradient across the clay, water flows from low to high salt concentration. The degree of semi-permeability is described by the reflection coefficient a, which ranges from 0 (no osmosis) to 1 (no solute transport). 

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