Aqueous phase ionic strength

The rate of decrease of / is directly related to the ionic strength of aqueous phase. Ionic strength, p, is related to the concentration of individual salt ions and the square of the ionic charge (z) of each ion ... 

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. 

Aqueous-phase ionic strength for which the constants arc valid. The entry should be regarded as approximate, since in many cases / q varied over a range. A zero indicates that either activity coefficients were calculated and used in the calculation or the aqueous-phase ionic strength in the experimental range extended down to about 0.003 M or lower. 

These are often assumed to be constant during reaction, although they sometimes vary with aqueous phase ionic strength (Asai et al., 1991, 1992) and temperature (Wang and Yang, 1991a). 

Aqueous phase - Ionic strength = O.IM with HCIO4, NaOH, and NaClOj).. The aqueous phase was sometimes buffered with 1 ml of O.UI anlllnlum perchlorate, sodium acetate, or hydrozlnlum perchlorate per 15 ml. 

Retention and stereoselectivity on the BSA columns can be changed by the use of additives to the aqueous mobile phase (30). Hydrophobic compounds generally are highly retained on the BSA, and a mobile-phase modifier such as 1-propanol can be added to obtain reasonable retention times. The retention and optical resolution of charged solutes such as carboxyUc acids or amines can be controlled by pH and ionic strength of the mobile phase. 

Cross-flow-elec trofiltratiou (CF-EF) is the multifunctional separation process which combines the electrophoretic migration present in elec trofiltration with the particle diffusion and radial-migration forces present in cross-flow filtration (CFF) (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears later in this section) in order to reduce further the formation of filter cake. Cross-flow-electrofiltratiou can even eliminate the formation of filter cake entirely. This process should find application in the filtration of suspensions when there are charged particles as well as a relatively low conduc tivity in the continuous phase. Low conductivity in the continuous phase is necessary in order to minimize the amount of elec trical power necessaiy to sustain the elec tric field. Low-ionic-strength aqueous media and nonaqueous suspending media fulfill this requirement. 

The theory of rate measurements by electrochemistry is mathematically quite difficult, although the experimental measurements are straightforward. The techniques are widely applicable, because conditions can be found for which most compounds are electroactive. However, many questionable kinetic results have been reported, and some of these may be a consequence of unsuitable approximations in applying theory. Another consideration is that these methods are mainly applicable to aqueous solutions at high ionic strengths and that the reactions being observed are not bulk phase reactions but are taking place in a layer of molecular dimensions near the electrode surface. Despite such limitations, useful kinetic results have been obtained. 

The actual characteristics of REV produced depend on a number of factors such as choice of lipids (% cholesterol and charged lipids), lipid concentration used in the organic solvent, rate of evaporation, and ionic strength of the aqueous phase (Szoka and Papahadjopoulos, 1980). Modifications of this REV technique were proposed by several groups. The SPLV (stable plurilamellar vesicles) method consists of bath-sonicating an emulsion of the aqueous phase in an ether solution of lipid while evaporating the ether (Griiner et al., 1985). 

Because a chemical step is imposed on top of the physical distribution process of partition, there is a great potential for selectivity, as noted by Schill et al, (49>50), Such factors as pH, type and composition of the organic phase, and ionic strength of the aqueous phase can be used to control relative retention. The concentration and type of counterion mainly control the absolute retention. 

Gangue minerals and salinity give constraints on the pH range. The thermochemical stability field of adularia, sericite and kaolinite depends on temperature, ionic strength, pH and potassium ion concentration of the aqueous phase. The potassium ion concentration is estimated from the empirical relation of Na+/K+ obtained from analyses of geothermal waters (White, 1965 Ellis, 1969 Fournier and Truesdell, 1973), experimental data on rock-water interactions (e.g., Mottl and Holland, 1978) and assuming that salinity of inclusion fluids is equal to ffZNa+ -h m + in which m is molal concentration. From these data potassium ion concentration was assumed to be 0.1 and 0.2 mol/kg H2O for 200°C and 250°C. 

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