Osmotic correction

Evans, E.A. and Waugh, R. 1977. Osmotic correction to elastic area compressibility measurements on red cell membrane. Biophys. J. 20 307-313. 

The problems involved in formulating a consistent theory of binding are illustrated when one measures the thermodynamic and dynamic properties of a limited number of polyelectrolytes with different counter-ions and then attempts to formulate a simple theory. For example, Gregor measured the selective uptake, self diffusion coefficients, electrical conductivity and electro-osmotic coefficients of a number of different ions in ion-exchange membrane and resin systems. The measurement of selective uptake is unequivocal and its correlation with binding is straightforward. Data on self-diffusion coefficients are complicated to interpret because the narrow pores of these insolu-bilized polyelectrolytes place steric and hydrodynamic restrictions upon the diffusive process. These can be overcome, at least in a semi-quantitative manner, by the use of appropriate correction terms [7]. The measurement of the electro-osmotic coefficient is simple and its interpretation is similarly straightforward. Data on electrical conductivity require interpretation because of the steric and hydrodynamic restraints of the pore nature of the system there is an electro-osmotic correction to the electrical conductivity. Table I tabulates normalized values for different counter-ions with... 

Expression (2.114) does not include the osmotic correction, proposed in [262] for consideration of fluctuation correlation radii changes. This eorreetion [141] is taken into account in the increase of the absolute Aripi value and the deerease of the Aricr and Arisp values. Obviously, Aricr, Arisp and Aria condition the mixture viseosity increase, while Aripi conditions the deerease of viscosity. The resultant value of viseosity is based on all these corrections. 

Since capillary tubing is involved in osmotic experiments, there are several points pertaining to this feature that should be noted. First, tubes that are carefully matched in diameter should be used so that no correction for surface tension effects need be considered. Next it should be appreciated that an equilibrium osmotic pressure can develop in a capillary tube with a minimum flow of solvent, and therefore the measured value of II applies to the solution as prepared. The pressure, of course, is independent of the cross-sectional area of the liquid column, but if too much solvent transfer were involved, then the effects of dilution would also have to be considered. Now let us examine the practical units that are used to express the concentration of solutions in these experiments. 

What makes the latter items particularly important is the fact that the charge and electrolyte content of an unknown polymer may not be known hence it is important to design an osmotic pressure experiment correctly for such a system. It is often easier to add swamping amounts of electrolyte than to totally eliminate all traces of electrolyte. Under the former conditions a true molecular weight is obtained. Trouble arises only when the experimenter is indifferent toward indifferent electrolyte this sort of carelessness can be the source of much confusion. 

Uses of lactose production by appHcation include baby and infant formulations (30%), human food (30%), pharmaceuticals (25%), and fermentation and animal feed (15%) (39). It is used as a diluent in tablets and capsules to correct the balance between carbohydrate and proteins in cow-milk-based breast milk replacers, and to increase osmotic property or viscosity without adding excessive sweetness. It has also been used as a carrier for flavorings. 

The similarity between the plots of c/r vs. c shown in Figs. 47 and 48 and those for tc/c vs. c shown in Figs. 38 and 39 is apparent. Deviations from ideality (i.e., the changes in iz/c and in c/r with c) have the same origin for both types of measurements. As with the osmotic pressure-concentration ratio, the change of c/r with c may be reduced by choosing a poor solvent. A further advantage of a poor solvent enters because of the smaller size assumed by the polymer molecule in a poor solvent environment, which reduces the dissymmetry correction. 

Van t Hoff introduced the correction factor i for electrolyte solutions the measured quantity (e.g. the osmotic pressure, Jt) must be divided by this factor to obtain agreement with the theory of dilute solutions of nonelectrolytes (jt/i = RTc). For the dilute solutions of some electrolytes (now called strong), this factor approaches small integers. Thus, for a dilute sodium chloride solution with concentration c, an osmotic pressure of 2RTc was always measured, which could readily be explained by the fact that the solution, in fact, actually contains twice the number of species corresponding to concentration c calculated in the usual manner from the weighed amount of substance dissolved in the solution. Small deviations from integral numbers were attributed to experimental errors (they are now attributed to the effect of the activity coefficient). 

The density correction is extremely important in such low osmotic-pressure measurements, but has been infrequently applied. 

Treatment of hyponatremia is associated with a risk of osmotic demyelina-tion syndrome, a severe neurologic complication that can develop if the rate of serum sodium correction exceeds 8 to 12 mEq/L within 24 hours. 

White and Vincent2 provided a method for readily finding the correct volume of water in which to dissolve a drug to produce a solution iso-osmotic with tears, followed by the addition of an isotonic vehicle to bring the solution to the final volume. The volume (V) of isotonic solution that can be prepared from any given drug is obtained by the equation ... 

It is fortunate that theory has been extended to take into account selective interactions in multicomponent systems, and it is seen from Eq. (91) (which is the expression used for the plots in Fig. 42 b) that the intercept at infinite dilution of protein or other solute does give the reciprocal of its correct molecular weight M2. This procedure is a straightforward one whereby one specifies within the constant K [Eq. (24)] a specific refractive index increment (9n7dc2)TiM. The subscript (i (a shorter way of writing subscripts jUj and ju3) signifies that the increments are to be taken at constant chemical potential of all diffusible solutes, that is, the components other than the polymer. This constitutes the osmotic pressure condition whereby only the macromolecule (component-2) is non-diffusible through a semi-permeable membrane. The quantity... 

In natural waters the situation is similar the ionic strength of most surface waters is so low that the activity of H20(l) can be set equal to unity. A correction may be necessary in the case of seawater, where a sufficiently good approximation for the osmotic coefficient may be obtained by considering NaCl as the dominant electrolyte. 

Equilibrium Dialysis Standard ED High-throughput, 96-well format. Long incubation time - compound instability and plasma degradation. Issues of pH drift and osmotic volume shifts (can be corrected for). Membrane adsorption/non-specific binding. [30-32]... 

Patients who present with heat exhaustion require fluid resuscitation. An attempt should be made to assess the amount of salt depletion and dehydration. This may be difficult clinically although the presence of symptoms such as muscle cramps in sodium depletion, and signs such as loss of tissue turgor may help. Laboratory measurement of sodium, urea, creatinine and haematocrit are the best guide. Pre-renal renal impairment is common. Treatment usually requires 5-10 1 of oral or intravenous isotonic fluids in the first 24 hours. In severe hyponatraemia the rapid correction of sodium should be carefully monitored with frequent sodium measurements and a reduction in fluid infusion rate if necessary to reduce the risk of osmotic demyelination (central pontine myelinol-ysis). 

Over the last 20-30 years not too much effort has been made concerning the determination of standard potentials. It is mostly due to the funding policy all over the world, which directs the sources to new and fashionable research and practically neglects support for the quest for accurate fundamental data. A notable recent exception is the work described in Ref. 1, in which the standard potential of the cell Zn(Hg)jc (two phase) I ZnS O4 (aq) PbS O4 (s) Pb(Hg)jc (two phase) has been determined. Besides the measurements of electromotive force, determinations of the solubility, solubiKty products, osmotic coefficients, water activities, and mean activity coefficients have been carried out and compared with the previous data. The detailed analysis reveals that the uncertainties in some fundamental data such as the mean activity coefficient of ZnS04, the solubility product of Hg2S04, or even the dissociation constant of HS04 can cause uncertainties in the f " " values as high as 3-4 mV. The author recommends this comprehensive treatise to anybody who wants to go deeply into the correct determination of f " " values. 

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