At varying salt concentrations

Figure 6.13 SEC results of permeates of the 1 kDa UF membrane at varied salt concentration (15 mgL NOM concentrate).

Figure 8. Dependence of viscosity on the shear rate at varying salt concentrations (a) copolymer ofm = 6 with Jbes = 20 mol %, Cp = 125 g/L (h) copolymer ofm = 25 with fj)E25 = 20 mol %, Cp = 25.0 g/L.

A series of gas solubility measurements was carried out by varying salt concentration at a fixed solvent composition. Such a measurement was repeated at various solvent compositions. 

Note that if Kf has been determined from solubility measurements, ywsaU is strictly valid only for saturated conditions. For dilute solutions y,wsalt can be determined from measurements of air-water or organic solvent-water partition constants at different salt concentrations. From the few compounds for which ywsa,t has been determined by both solubility and air-water or solvent-water partitioning experiments, because of the large scatter in the data, it is not clear whether Kf varies with organic solute concentration. It can, however, be concluded that, if there is an effect, it is not very large. 

A commonly employed first separation step is ammonium sulfate precipitation. This technique exploits the fact that the solubility of most proteins is lowered at high salt concentrations. As the salt concentration is increased, a point is reached where the protein comes out of solution and precipitates. The concentration of salt required for this salting out effect varies from protein to protein, and thus this procedure can be used to fractionate a mixture of proteins. For example, 0.8 M ammonium sulfate precipitates out the clotting protein fibrinogen from blood serum, whereas 2.4 M ammonium sulfate is required to precipitate albumin. Salting out is also sometimes used at later stages in a purification procedure to concentrate a dilute solution of the protein since the protein precipitates and can then be redissolved in a smaller volume of buffer. 

There are other complications. The salt, besides forming association complexes with solution molecules, possibly could also alter or even destroy already-existing self-interactions of the molecules of a volatile component either with themselves or with those of the other feed component. An example is the associated structure in which liquid water and to a lesser extent some alcohols exist. The effects of salt ions on water-water, water-alcohol, and alcohol-alcohol complexing, for example, must be profound at higher salt concentrations, and will vary in a given system with salt concentration and with alcohol-water proportionality in the liquid. Also, associations of several, rather than just pairs, of liquid-phase species may form. The full complexity of what initially seems to be a rather simple system finally becomes evident when it is considered that the sum of individual effects which make up the overall effect of the salt on the composition of the equilibrium vapor even in a given system are functions of the relative proportions of all components present and vary with liquid phase composition over the entire range involved in the separation. 

We investigate here the dynamic behavior of fully charged NaPSS solutions with multivalent salt (LaCl3) measured by quasi-elastic light scattering. The bimodal decay of the correlation function of polyelectrolyte concentration (C) at constant salt concentration (Cs) is studied first. The ratio Cs/C varies from 0.2 to 10 2. Then the dynamics of the solution at constant C as a function of Cs from Cs/C approximately 10 2 to 0.2 are investigated. 

Fig. 25. The effect of urea and ionic strength on the CD spectrum of spinach ferredoxin (302). The data was recorded anaerobically for protein solutions at pH 7.3 and 23 °C. Spectra labelled with varying salt concentrations are for the protein dissolved in 5 M urea...

---