Eluotropic values

The concept of eluotropic strength has been invoked here without a rigorous definition. Snyder (130) developed a series of eluotropic values for solvents by using retention values measured on alumina columns. Colin and Guiochon (86) used a definition similar to that of Snyder to evaluate eluotropic strengths of methanol-water mixtures on various column surfaces. The eluotropic strength, e, was calculated by using the equation... 

Eluents used in reversed-phase chromatography with bonded nonpolar stationary phases are genei ly polar solvents or mixtures) of polar solvents, such as acetonitrile, with water. The properties of numerous neat solvents of interest, their sources, and their virtues in teversed-phase chromatography have been reviewed (128). Properties of pure solvents which may be of value as eluents are summiuized in Table. VII. The most significant properties are surface tension, dielectric constant, viscosity, and eluotropic value. Horvath e/ al. 107) adapted a theory of solvent effects to consider the role of the mobile phase in determinmg the absolute retention and the selectivity found in reversed-phase chromatography. 

The following table provides, for comparative purposes, eluotropic values on bonded octadecyl silane (ODS) and octyl silane (OS) for common solvents.12... 

LC, liquid chromatography GC, gas chromatography E, extraction F, filtration CZE, capillary zone electrophoresis 8°, eluotropic value Rl, refractive index dzs Ci density BP, boiling point tj, viscosity , dielectric constant. 

In conclusion, eluotropic values, although derived ftom complex mathematical relationships and difficult to generate, offer a r id means of efficiently investigating different solvents. The use of nomograms is key for multicomponent mobile phases. 

The following table provides, for comparative and interpretive purposes, eluotropic values on bonded octadecylsilane (ODS) and octylsilane (OS) for common solvents used in HPLC (Refs. 1-3). For additional information on common, specific and chiral stationary phases for HPLC, and for solvents, derivatizing reagents, and detectors, see Ref. 3. 

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