Ionic solutes quaternary systems

As a brief conclusion it can be noted that many nonaqueous microemulsions reported do not seem to contain an organized structure, being simply molecular solutions. Since the degree of organization already in many aqueous microemulsion is low, in particular for quaternary systems containing ionic surfactant and cosurfactant, this is not really surprising. 

Vega and Funk (1974) presented a thermodynamic correlation for solid-liquid equilibria in concentrated aqueous salt solutions and applied the correlation to the six-component system containing Na+, K+, Mg +, NO, SO " from 0 to 50 °C. In their correlation they define an activity coefficient as if the given salt were a non-electrolyte, although this new quantity is easily related to the mean ionic activity coefficient 7 . The derived parameters are claimed to enable correlation of equilibria for ternary and quaternary systems with errors in liquid phase composition of less than 2g salt per 100 g water. 

For the separation of anions of weak protolytes such as carboxylates, a pH close to neutral is chosen to ensure that the solutes are in ionic form. Quaternary ammonium ions such as tetrabutylammonium are most often used as counterions, as in the example given in Figure 5, which shows the separation of benzoic acid and three structurally related carboxylic acids. A mixture of acetonitrile and phosphate buffer of pH 6.0 is the mobile phase. These few applications illustrate the kind of phase systems being used with anionic or cationic counterions. The hydrophobicity... 

Isothermal microcalorimetry has also been used to determine the crystallinity of mixtures of amorphous and crystalline antibiotics [63]. DSC could not be used for this process since the samples decomposed prior to melting and an accurate quantification of the heat of fusion could not be determined. In contrast to studies carried out by Hogan et al. [ 64 ], in this case, it was shown that the heat of solution was not dependent on residual water content. The importance of initial water content is greatest when dealing with hydratable ionic species, since sodium and quaternary ammonium salts have very high heats of hydration. Therefore, before performing any analysis one must care to identify the extent of residual solvents or water present, as well as their effects on the heats of solution in the chosen system. 

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