Solute reflection coefficient measure

Traceability has also been established for ratio measurements such as reflection coefficient, absorbance and angle measurements. Different techniques to establish traceability are used in different fields of measurement and it is a mistake to look for a one size fits all solution. 

These equations correspond, respectively, to the set of Eq. (10.87) for the case of dilute solutions. The value of reflection coefficient cr must depend on the nature of both the solute and the membrane. For the case of volume flow in the absence of the concentration gradient in the permeant solute (AIIS = 0), we see that the quantity (1 - cr) is a direct measure of the extent of coupling between the solute flow and the volume flow. If the membrane is completely nonselective, then a = 0 if the membrane is perfectly selective, permeable only to the solvent, then cr = 1. In most cases, a will lie between 0 and 1. 

If we vary n° and measure V, we can then use Equation 3.45 to obtain the reflection coefficients for various nonelectrolytes in the external solution. 

Myoglobin, cytochrome-C, inulin, and vitamin B-12 were the solutes studied in saline, calf serum, and BSA systems at 37 C and pH 7.4. Observed solute rejections were corrected to intrinsic values by using uniform-wall-flux boundary layer theory for the developing and fully-developed asymptotic regions. The Splegler-Kedem equation ( ) for rejection versus volume flow was used to calculate reflection coefficients and diffusive permeabilities for each solute. There was no significant difference between rejection parameters measured in saline and protein solutions. 

A polarity ranking is not possible based only on dielectric constant and dipole moment because they do not take into account H-bonding thus, polarity series are often constructed empirically, using such factors as the solvent strength parameter obtained from the observed ability of various solvents to elute solutes from aluminum oxide absorbent. However, for environmental chemicals, a numerical index for polarity does not exist only the consequences of polarity, as reflected in measureable properties such as water solubility and octanol-water partition coefficient, are available for fate predictions. 

Polystyrene Solutions 23—300 MHz. Moore et al. (85,86) obtained complex moduli data in the range of 23-300 MHz by measuring the complex reflection coefficient of shear waves reflected from a solid-liquid interface. The measurements were performed for solutions of polystyrene in dibutyl phthalate over the concentration range of 3-20 Vol.-% (86). The result is shown in Fig. 4.4 where (rf — v1 rjs)/ (t] - vt rjs) is plotted against f(t] — v1 f]s) M/cR T, vx being the volume fraction of the solvent and / the frequency in Hz. It is seen that the... 

The Debye-Huckel theory gives a calculation of the activity coefficients of individual ions. However, although the individual concentrations of the ions of an electrolyte solution can be measured, experiment cannot measme the individual activity coefficients. It does, however, furnish a sort of average value of the activity coefficient, called the mean activity coefficient, for the electrolyte as a whole. The term mean is not used in its common sense of an average quantity, but is used in a different sense which reflects the number of ions which result from each given formula. Such mean activity coefficients are related to the individual activity coefficients in a manner dictated by the stoichiometry of the electrolyte. 

Next, one frequently would like to be able to make some assessment of the accuracy of a set of experimental vapor-liquid or activity coefficient measurements. Basic thermodynamic theory (as opposed to the solution modeling of Chapter 9) provides no means of predicting the values of liquid-phase activity coefficients to which the experimental results could be compared. Also, since the liquid solution models discussed in Chapter 9 only approximate real solution behavior, any discrepancy between these models and experiment is undoubtedly more a reflection of the inadequacy of the model than a test of the experimental results. 

ANL s ultrasonic viscometer is a nonintrusive in-line device that measures both fluid density and viscosity. The design of the viscometer is based on a technique that measures acoustic and shear impedance. The technique was first applied by Moore and McSkimin (1970) to measure dynamic shear properties of solvents and polystyrene solutions. The reflections of incident ultrasonic shear (1-10 MHz) and longitudinal waves (1 MHz), launched toward the surfaces of two transducer wedges that are in contact with the fluid, are measured. The reflection coefficients, along with the speed of sound in the fluid, are used to calculate fluid density and viscosity. Oblique incidence was commonly used because of better sensitivity, but mode-converted waves often occur in wedges that do not exhibit perfect crystal structure and lack well-polished surfaces. For practical applications, we use the normal-incidence arrangement. 

In this Section, it is implicitly assumed that the mass transport resistance at the fluid-membrane interface on either side of the membrane is negligible. Also the following is information that is made available publicly by the membrane manufacturers, when not otherwise noted. As in technical processes, mass transport across semipermeable medical membranes is conveniently related to the concentration and pressme driving forces according to irreversible thermodynamics. Hence, for a two-component mixture the solute and solvent capacity to permeate a semipermeable membrane under an applied pressure and concentration gradient across the membrane can be expressed in terms of the following three parameters Lp, hydraulic permeability Pm, diffusive permeability and a, Staverman reflection coefficient (Kedem and Katchalski, 1958). All of them are more accurately measured experimentally because a limited knowledge of membrane stmcture means that theoretical models provide rather inaccurate predictions. 

The Staverman reflection coefficient, o, measures the extent to which the membrane rejects a given solute purely transported by convection. Solutes fully rejected by the membrane feature o = 1. Solutes freely permeating the membrane feature ct = 0. Membrane rejection toward a given solute is experimentally assessed in the course of pure filtration experiments in terms of its rejection coefficient R, or its sieving coefficient S, with S = —R being the permeate-to-retentate solute concentration ratio. In fact, R is related to a as follows (Spiegler and Kedem, 1996) ... 

Penetration of a substance is measured by the permeability coefficient, P, which could be converted to a measurable diffusional coefficient, D, if Pick s law applied strictly. In the more complex situation of a membrane barrier, Kedem and Katchalsky (1958, 1961) have shown that under rigidly controlled conditions there exist at least three parameters which must be considered when characterizing the behavior of a membrane toward a particular solute (1) the interaction between membrane and solvent (2) the interaction between solute and membrane and (3) the interaction between solute and solvent. The reflection coefficient, (T, measures relative rates of solute and solvent permeabilities in the system (Staverman, 1952) and is therefore a measure of semipermeability. Lp is the mechanical coefficient of filtration or pressure filtration coefficient, and co is the solute mobility or solute diffusional coefficient. In the case of living membranes, conditions such as volume flow, osmotic gradients, and cell volume can be manipulated in order to measure the phenomenological coefficients cr, o>, and Lp. Detailed discussions of the theories, methods, and problems involved in such... 

Lipophilicity is a molecular property expressing the relative affinity of solutes for an aqueous phase and an organic, water-immiscible solvent. As such, lipophilicity encodes most of the intermolecular forces that can take place between a solute and a solvent, and represents the affinity of a molecule for a lipophilic environment. This parameter is commonly measured by its distribution behavior in a biphasic system, described by the partition coefficient of the species X, P. Thermodynamically, is defined as a constant relating the activity of a solute in two immiscible phases at equilibrium [111,112]. By convention, P is given with the organic phase as numerator, so that a positive value for log P reflects a preference for the lipid phase ... 

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