Binary solvent

Fig. 8. Pseudo-binary (solvent-free)jy-x phase diagrams for determining which component is to be the distillate where (—) is the 45° line, (a) No solvent (b) and (c) sufficient solvent to eliminate the pseudo-a2eotiope where the distillate is component 1 and component 2, respectively (51) and (d) experimental VLE data for cyclohexane—ben2ene where A, B, C, and D represent 0, 30, 50, and 90 mol % aniline, respectively (52).

Here, the solute S is in dilute solution, and tire equation can be used across the enthe composition range of tire A-B binary solvent, when Aa + Ab is close to one. When the concentration of the dilute solute is increased, the more concentrated solution can be calculated from Toop s equation (1965) in the form... 

Figure 16. Graphs Showing the Distribution Coefficient of n-PentanoI between Water and Three Binary Solvent Mixtures Plotted against Solvent Composition...

Practically a more convenient way of expressing solute retention in terms of solvent concentration for a binary solvent mixture as the mobile phase is to use the inverse of equation (11), i.e.. 

The bulk properties of mixed solvents, especially of binary solvent mixtures of water and organic solvents, are often needed. Many dielectric constant measurements have been made on such binary mixtures. The surface tension of aqueous binary mixtures can be quantitatively related to composition. ... 

Figure 8-4. Fraction of total base present as hydroxide as a function of the percentage of water in the binary solvent, lor ethanol-water and methanol-water mixtures. ...

This approach to solution chemistry was largely developed by Hildebrand in his regular solution theory. A regular solution is one whose entropy of mixing is ideal and whose enthalpy of mixing is nonideal. Consider a binary solvent of components 1 and 2. Let i and 2 be numbers of moles of 1 and 2, 4>, and 4>2 their volume fractions in the mixture, and Vi, V2 their molar volumes. This treatment follows Shinoda. ... 

It is found that m is solvent dependent.The R part of substrate RX cannot be made drastically different from that in the model substrate without causing dispersion into separate lines for different binary solvents. The leaving group X introduces another type of specificity. 

Langhals has described a remarkable relationship of most of the empirieal solvent parameters [Z. t (30), Y, ete.] to composition in binary solvent mixtures ... 

These workers used binary solvent systems over a range of mole fractions to determine, for each solute, the constants a and b of equation (8.2). For methyl and phenacyl esters, TLC was used, while overpressured layer chromatography (OPLC) was used for dansyl amino acids. Nurok and co-workers (11) also evaluated how the quality of a simulated separation varies with changing solvent strength by using the inverse distance function (IDF) or planar response function (PRF), as follows ... 

If S[ is a weak base (low DN) and S2 is a strong base, cations are selectively solvated by S2 conversely, if Sj is a good acceptor (high AN) it will preferentially solvate the anion. As a consequence, the Stokes radii of ions generally change with the composition of a binary solvent. 

The main problem in the study of the role of these parameters in electrolyte conductivity is their interdependence. A change in composition of a binary solvent changes viscosity, along with the permittivity, ion-ion association, and ion solvation, which may be preferential for one of the two solvents and therefore also changes the Stokes radii of the ions. 

In our discussion of the coexistence curve, we tacitly assumed that at least one liquid phase can exist for any composition. However, since component 2 is a supercritical gas, the physically allowable liquid compositions are limited by the solubility of the gas in the binary solvent mixture. As the pressure rises, the solubility of the gas increases, thereby enlarging the composition range which permits the existence of a liquid phase. 

The value of a12 affects the total pressure required to achieve any specified degree of separation. This is illustrated in Fig. 32. A binary solvent separates into phases a and b at lower pressures as oc12 increases. This follows from the fact that a large ac12 indicates that the gas is much more soluble than predicted by Henry s law. 

Although chromatographic conditions are extremely variable and widely discussed in the literature, broad trends may nonetheless be perceived. A binary solvent such as acidified water/acidified methanol or acidified water/acidified acetonitrile is primarily used because acidification of the solvent converts nearly all anthocyanidins... 

They showed further that the limiting slope (RTA2) of the plot of the osmotic pressure-concentration ratio tz/c against the polymer concentration in a binary solvent mixture should be proportional to the value of the quantity on the left side of Eq. (17),f with V2 representing the volume fraction of solvent in the nonsolvent-solvent mixture which is in osmotic equilibrium with the solution. The composition of the liquid medium outside the polymer molecules in a dilute solution must likewise be given by V2. The composition of the solvent mixture within the domains of the polymer molecules may differ slightly from that outside owing to selective absorption of solvent in preference to the nonsolvent. This internal composition is not directly of concern here. If the solution is made sufficiently dilute, the external nonsolvent-solvent composition v2 = l—Vi) will be practically equal to the over-all solvent composition for the solution as a whole. Hence... 

Recently, Janjic et al. published some papers [33-36] on the influence of the stationary and mobile phase composition on the solvent strength parameter e° and SP, the system parameter (SP = log xjx, where and denote the mole fractions of the modiher in the stationary and the mobile phase, respectively) in normal phase and reversed-phase column chromatography. They established a linear dependence between SP and the Snyder s solvent strength parameters e° by performing experiments with binary solvent mixtures on silica and alumina layers. 

FIGURE 4.10 Mobile phase selection by microcircular technique, a. Sample of known composition A = nonpolar compound A1 = n-hexane A2 = acetone A3 = n-hexane-acetone, 60-1-40, v/v B = polar compound B1 = methanol B2 = water B3 = methanol-water, 70-1-30, v/v. b. Sample of unknown composition testing with solvents of different Snyder s groups and binary solvent mixture. 

Catalan, J., Diaz, C., Garcia, F. Characterization of binary solvent mixmres of DM SO with water and other cosolvents./. Org. Chem. 2001, 66, 5846-5852. 

Solvent optimization in reversed-phase liquid chromatography is commenced by selecting a binary mobile phase of the correct solvent strength to elute the seuaple with an acceptable range of capacity. factor values (1 < k <10 in general or 1 < k < 20 when a larger separation capacity is required). Transfer rules (section 4.6.1) are then used to calculate the composition of other isoeluotropic binary solvents with complementary selectivity. In practice, methanol, acetonitrile and tetrahydrofuran are chosen as the selectivity adjusting solvents blended in different... 

Figur 4.31 Sequential, isocratic elution using a stepwise reduction in solvent strength to identify a binary solvent of acceptable strength for elution of a five ca x>nent mixture. In this example the column holdup time was 1 min.

Figure 5.5 Two Bethods for generating binary solvent gradients.

LDPE Chimassorb 944 Various binary solvent mixtures [458]... 

In the resulting binary solvent mixtures of either OSM or TSM micronising step procedures, one apolar component (n-hexane or n-heptane) serves to give high swelling-melting power to the polymer but does not heat under microwave irradiation. The second polar component (ethyl acetate, acetone, and isopropyl alcohol) has... 

For hydrophobic, (virtually) nonionizable substances [i.e., those that show no ionic species of significance in the pH range 1 to 10 (e.g., diazepam)], solubility can usually be improved by addition of nonpolar solvents. Aside from solubility, stability is also affected by solvents in either a favorable or a nonfavorable direction [6], Theoretical equations for solubility in water [7] and in binary solvents [8] have been reported in literature, but in general the approach in preformulation is pseudoempirical. Most often the solubility changes as the concentration of nonpolar solvent C2, increases. For binary systems it may simply be a monotonely changing function [9], as shown in Fig. 2. The solubility is usually tied to the dielectric constant, and in a case such as that shown by the squares, the solubility is often log-linear when plotted as a function of inverse dielectric constant, E, that is,... 

VS Vadalkar, MG Kulkarni, SS Bhagwat. Anomalous sorption of binary solvents in glassy polymers Interpretation of solute release at constant rates. Polymer 34 4300-4306, 1993. 

K Yoshimura, K Sekimoto. Coupling between diffusion and deformation of gels in binary solvents—A model study. J Chem Phys 101 4407-4417, 1994. 

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