Eluotropic series for alumina

A ranking of solvents or solvent mixtures in order of increasing eluent strength for a particular stationary phase is known as an eluotropic series. (In Chapter 4, Fig. 4-7 included an eluotropic series for alumina.) The list in Table 5-3 is the eluotropic series for various compounds on silica (20). Since silica is a polar material capable of hydrogen bonding and ion-exchange... 

Selection of Chromatographic Systems 137 Table 3.26 Eluotropic series for alumina. 

Binary Solvent Eluotropic Series for Adsorption on Water-Deactivated Alumina (a = 0.6) Calculated Values from Eq. (8-10)... 

Table 8-3 presents relative eluotropic series for separations on charcoal and polyamide. The series for charcoal is almost the reverse of that shown for alumina in Table 8-1. Solvent strength on charcoal is seen to increase with the size of the solvent molecule, and there is a good correlation between solvent strength and the calculated area (A,) required by an adsorbed solvent molecule. Jermyn (24) has reported additional data on the relative strengths of various solvents for adsorption on charcoal. The...

Equation 4.13 and Equation 4.14 were tested for a series of mobile phases on alumina [29-31] and silica gel [32]. Two eluotropic series of solvent binary mixtures for alumina (a = 0.6) and silica gel (a = 0.7) have been calculated by using Equation 4.13, and the obtained data can be used to establish many such series or series of other selectivities [13,28],... 

Eluotropic series can be expressed more precisely by the Snyder parameter e°, given in Table 4.2 for alumina and silica gel. It is important to take into account eluotropic series and know some rules when solvents are used according to this table [16,17] ... 

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... 

The following table contains the common solvents used in thin-layer chromatography, with a measure of their strengths on silica gel and alumina. The solvent strength parameter, s°, is defined as the relative energy of adsorption per unit area of standard adsorbent.13 It is defined as zero on alumina when pentane is used as the solvent. This series is what was called the eluotropic series in the older literature. For convenience, the solvent viscosity is also provided. Note that the viscosity is tabulated in cP for the convenience of most users. This is equivalent to mPasec in the SI convention. Additional data on these solvents may be found in the tables on high-performance liquid chromatography. 

Table A-11. Eluotropic solvent series for hydrophilic adsorbents such as alumina or silica, listed in order of increasing eluting power of the solvent , quantitatively measured by Snyder s empirical eluant strength parameter °. ...

It is well recognized that the eluotropic series of solvents, according to Snyder, is suited for monoactive site-type adsorbents, but in the case of multiactive site-type adsorbents (e.g., alumina), their imperfection becomes acute. Thus for multiactive-site-type adsorbents, the eluotropic series sequence and eluent strength values are highly dependent on the class of test solutes employed. ... 

A practical eluotropic series of solvents, based on the expended solubility parameter concept, was reported. This series was defined based on partial specific solubility parameter (5 ) that is equal to the sum of Keeson (5q) and acid-base (2 a b)> which represents the contribution to interaction forces introduced to characterize the solute, the mobile, and the stationary phase in liquid-solid chromatography. Exactly the same two interaction forces define e° and, consequently, there should exist a direct relation between e° and s = o+2 a b- Unfortunately, the general correlation for all the solvents on alumina is poor (r =0.75). 

The derivation of Eq. (8-3) assumes that the solvent Strength parameter e" can assume different values for different adsorbents. The possibility of gross changes in eluotropic series between different adsorbents is likewise not precluded. Table 8-2 presents some quantitative e data for polar adsorbents other than alumina. While it is apparent that these e values... 

Thus, stronger adsorption of the mobile phase decreases adsorption of the solute. Solvents can be classed according to their strength of adsorption. Such a quantitative classification is referred to as an eluotropic series. Table 21.3 is an abbreviated eluo-tropic series specifically for alumina as the adsorbent, but qualitatively this series holds for other polar adsorbents as well [4]. 

III-3 and 111-4) provides several eluotropic solvent series with equal spacing of solvent strength for adsorption on both alumina and silica. 

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