Solvent strength of binary mixture

According to L.R. Snyder (Snyder, 1968) it is possible to calculate the solvent strength of binary mixtures using Eq. 4.5. 

Figure 10.5 Solvent strength of binary mixtures for reversed-phase chromatography.

The bulk solvent strength of binary and ternary supercritical mixtures, measured with the solvatochromic dye Nile Red (E ),... 

The usual A solvent in reversed-phase chromatography is water or aqueous buffer. The strength of binary mixtures is not a well defined function of %B but depends on analyte and stationary phase properties. Nevertheless, it is possible to give numerical... 

Figure 5. TLC retention factor Rp for poly(methyl methacrylate) on silicagel, as a function of the elution strength of binary solvent (carbontetrachloride, CCl )/ displacer (1,4-dioxane) mixtures. Note the steep increase in Rj, at Efj w 0.38, indicating a sharp adsorption/ desorption transition.

Tertiary systems. With methanol/carbon dioxide mixtures the addition of even the most polar additives has only a small impact on the mobile phase solvent strength as measured with Nile Red. With TFA concentrations below 1 to 2 % in methanol, ternary mixtures of TFA/methanol/carbon dioxide produce the same apparent solvent strength as binary methanol/carbon dioxide mixtures. As much as 5 or 10 % TFA in methanol is required to noticeably increase the solvent strength of TFA/methanol/carbon dioxide mixtures above those for binary methanol/carbon dioxide mixtures, as shown in Figure 4. 

Figure 3.20 Nomogram illustrating the solvent strength of various binary solvent mixtures for LSC. Vertical (dashed) line illustrates a series of iso-eluotropic solvents (see text). Figure taken from ref. [358]. Reprinted with permission.

A RAPID PROCEDURE FOR ESTIMATING THE SOLVENT STRENGTHS OF A SERIES OF BINARY MIXTURES. TABULATED VALUES FOR SEVERAL BINARY SOLVENT SYSTEMS... 

As part of their research in optimizing chromatographic methods, M.C. Breitkreitz and co-workers employed a mixture design to search for the MP composition that would give the best selectivity for a 10-component mixture separation (Breitkreitz et al., 2005). The organic solvents acetonitrile (ACN), methyl alcohol (MeOH) and tetrahydrofuran (THF) were used as water modifiers. Initially, the solvent strength of ACN in water was varied to produce a desirable separation power for all the solutes. Once this composition had been experimentally determined, the water contents of the other two solvents were predicted based on empirical relationships. In this manner, the pure components used to specify the design were, in fact, binary mixtures ACN H20, MeOH H20 and THF H20. 

It is possible to obtain a desired elution strength by mixing two solvents. A choice of binary mixtures is shown in Fig. 9.4. If, for example, a solvent strength of 8 = 0.4 is needed, this can be obtained by the following binary eluents ... 

Snyder, L.R. Glajch, J.L. Solvent strength of multicomponent mobile phases in liquid solid chromatography Binary-solvent mixtures and solvent locahzation. J. Chromatogr. 1981, 214, 1. 

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