Solvent modifier

Because extractive solvents work by altering the relative volatihty between the components to be distilled, a good solvent causes a substantial change in relative volatihty when present at moderate compositions. As seen from equation 3, the solvent modifies the relative volatihties by affecting the ratio of the hquid-phase activity coefficients yWhereas it is possible to find solvents which increase or decrease this ratio, it is usually preferable to select a solvent which accentuates the natural difference in vapor pressures between the components to be separated that is, a solvent that increases relative to when is favored, over one that increases relative to y. In the latter case, adding small amounts of the solvent actually makes the separation... 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

There is increasing interest in copolymer systems, which, due to their chemical heterogeneity, may require very complex eluent systems in order to dissolve the sample and ensure that the separation ensues hy a pure size exclusion mechanism. In these examples, the PLgel is also compatible with eluent systems containing mixed solvents of different polarity (including water as a cosolvent up to 10% hy volume) and in organic solvents modified with acids or bases (e.g., acetic or formic acid, triethanolamine) as it is stable in the pH range of 1-14. 

Figure 2. Sketch of an uncharged metal surface (simulated by the jellium model) covered by a macroscopic solvent layer, showing the components of the electric potential drop. 8%M is the surface potential of the metal modified by the solvent layer %s + 6%s is the surface potential of the solvent modified by the contact with the metal %s is the unmodified surface potential of the solvent layer at the external surface.

This theory is associated in its early protonic form with Franklin (1905, 1924). Later it was extended by Germaim (1925a,b) and then by Cady Elsey (1922,1928) to a more general form to include aprotic solvents. Cady Elsey describe an acid as a solute that, either by direct dissociation or by reaction with an ionizing solvent, increases the concentration of the solvent cation. In a similar fashion, a base increases the concentration of the solvent anion. Cady Elsey, in order to emphasize the importance of the solvent, modified the above defining equation to ... 

McCalley, D. V., Effect of organic solvent modifier and nature of solute on the performance of bonded silica reversed-phase columns for the analysis of strongly basic compounds by high-performance liquid chromatography, /. Chromatogr A, 738(2), 169, 1996. 

A problem that has been encountered in the use of single component SCFs is that those with easily attainable critical parameters are relatively nonpolar and the compounds which can be solubilised are therefore also limited by their polarity. This problem can be partially overcome by using solvent modifiers . The mechanism by which these modifiers work is complex and still subject of research. 

The main interest in cSFC comes from the high efficiency that can be obtained for involatile samples. The capillary column has the advantage of being able to chromatograph many analytes without additional solvent modifiers. cSFC generates two to three orders of magnitude more theoretical plates for a given separation than a typical packed column of 5 xm particles. 

T3 1 solvent modifier. with ionic functional groups. (See also Section 19.6.2). peptides, nucleic acids, proteins. Saccharides. 

Column pressure usually has little effect on enantioselectivity in SFC. However, pressure affects the density of the mobile phase and thus retention factor [44]. Therefore, similar to a modifier gradient, pressure or density programming can be used in fast separation of complex samples [106]. Later et al. [51] used density/temperature programming in capillary SFC. Berger and Deye [107] demonstrated that, in packed column SFC, the effect of modifier on retention was more significant than that of pressure. They also showed that the enhanced solvent strength of polar solvent-modified fluid was nof due fo an increase in densify, caused by fhe addition of fhe liquid phase modifier, buf mainly due fo fhe change in composition. 

FIGURE IS Plots of log k vs. % organic solvent modifier for methanoi, acetonitrile, and tetrahydrofuran. Reprinted with permission from Reference 7. 

Hansen, S. H., Gabel-Jensen, C., El-Sherbiny, D. T. M., and Pedersen-Bjergaard, S. (2001). Microemulsion electrokinetic chromatography - or solvent-modified micellar electrokinetic chromatography TrAC, Trends Anal. Chem. 20, 614—619. 

Calculation of Schematic Phase Diagrams for the Preparation of Solvent-Modified and Macroporous Thermosets via CIPS. . Guidehnes for the Preparation of Solvent-Modified and Macroporous Thermosets via CIPS. ... 

Selection Criteria for the Preparation of Solvent-Modified and Macroporous Epoxy Networks with Tailored Morphologies Prepared via CIPS. 

Toughness of Solvent-Modified and Macroporous Epoxies Prepared via CIPS. 

Calculation of Stress Distribution in Macroporous Epoxies Fracture Toughness of Solvent-Modified and Macroporous Epoxies Prepared via CIPS. 

In addition to the general procedure of the CIPS technique described in Fig. 1, the principle experimental procedure for the preparation of solvent-modified and macroporous epoxy networks via the CIPS technique is given below [49,50]. 

To overcome these problems a gradient oven was presented which allows one to find rapidly the real phase separation gap for a given set of polymer and solvent. These results may serve as general guidelines for the preparation of a wide variety of solvent-modified and macroporous thermosets with tailored morphologies via CIPS. 

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