Ionic strength aqueous systems

The interpretation of the above results is made more difficult by a supplementary phenomenon due to the aqueous phase ionic strength. Increasing the density of charges in the vicinity of the surfactant headgroups causes a screening effect not only between surfactant and protein but also in the repulsive interaction between surfactant polar heads they come closer and the micellar size decreases (43). As a consequence, Goklen and Hatton (48) noted a decrease in the amount of water in AOT system when increasing KCl concentration. However, it is difficult from these results to state precisely whether the decrease in protein extraction is due to the decrease of electrostatic interactions or to a size exclusion effect. 

Figure 8 shows results similar to the swelling equilibria curves for partially-ionized gels in aqueous salt solutions (Figure 3). In both cases, a large reduction in volume (gel volume, or polymer excluded volume) is induced by an increase in system ionic strength. Clearly, differences exist between the two cases, and the comparison is qualitative. Nevertheless, we see similarities between single-chain behavior and behavior of more complex aqueous/polymer systems.

Figure 1.93. /02-pH diagram with the stability fields of aqueous species in Na-K-H-S-Se-0 system for the conditions SS = 10 mol/kg H2O, ESe = 10 mol/kg H2O, ionic strength = 1, and temperature = 150°C. Dashed lines are the ratio ho-a i- /a i- in logarithmic units. Stability fields for native sulfur and native selenium and the boundaries between predominance regions of oxidized and reduced selenium species are omitted for clarity (Shikazono, 1978b). 

To use liposomes as delivery systems, drug is added during the formation process. Flydrophilic compounds usually reside in the aqueous portion of the vesicle, whereas hydrophobic species tend to remain in the lipid proteins. The physical characteristics and stability of lipsomal preparations depend on pH, ionic strength, the presence of divalent cations, and the nature of the phospholipids and additives used [45 47],... 

CE determination of pKa is new, compared to the other techniques [144—147]. It has the advantage of being a rather universal method since different detection systems can be coupled to CE. Because it is a separation technique, sample impurities seldom are a problem. A fused-silica capillary, with an inner diameter of 50-75 pm and 27-70 cm in length is filled with a dilute aqueous buffer solution (ionic strength... 

With an aqueous fluid phase of high ionic strength, the problem of obtaining activity coefficients may be circumvented simply by using apparent equilibrium constants expressed in terms of concentrations. This procedure is recommended for hydro-metallurgical systems in which complexation reactions are important, e.g., in ammonia, chloride, or sulfate solutions. 

A chemical equilibrium modeling system that can be used to perform calculations on low temperature (0-50°C), low to moderate ionic strength (<0.5 M) aqueous systems. 

The first part of the book contains basic solution theory and thermodynamics (Chapter 2) a survey of the effects on the distribution ratio of changes in parameter values, such as concentration of metals, complex formers and other reactants, pH, temperature, etc., (Chapter 3) measurement techniques, data collection, evaluation, and interpretation (Chapter 4) and kinetics (Chapter 5). The ionic strength is an essential factor in all aqueous systems, and how to cope... 

Extraction of metals from chloride solutions into kerosene containing trioctyl amine (TOA), as illustrated by Fig. 1.3, has found application in the production of pure Co and Ni metals from their ores, as discussed in Chapter 11. The aqueous phase contains the Co and Ni in addition to other metals in chloride solution, where the chloride concentration goes to 300 g/L (i.e., about 8.5 M). At this high aqueous ionic strength, a rigorous mathematical treatment of the system would require the use of activities in order to explain the extraction... 

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